Index

Electronics safety pages

    Materials used in electronics

    The materials used in electronics were selected for specific characteristics such as high dielectric strength, good electrical conductivity, poor electrical conductivity, good thermal conductivity, low melting point, etc. Since most electronics manufacturing is performed in industrial environments, it is assumed that dangerous substances will be treated appropriately.An awareness of materials hazards is therefore important to the individual experimenter and people responsible for electronics laboratorios and/or factory safety.Here are some dangrous substanced you might encounter in electronics work:

    • Solders: Solders include nowadays signifcant amount of lead (40-60%, is going to dissapear on some coming years). Lead causes significant health problems, including loss of mental functions. Don't stick the solder in your mouth!
    • Ceramics can be dangerous: One of the favorite ceramics used in electronics is Beryllium Oxide. This substance is a good electrical insulator and a good thermal conductor. It is also one of the most poisonous compounds you will ever encounter!
    • Soldering fume: Fumes from solvents are generally bad for you. The smoke from soldering (vaporized flux) is unpleasant and caustic.
    • Circuit board materials: Dust from filing plastic or glass-epoxy circuit boards is bad for your lungs.
    • Solvents: Most solvents are easily absorbed through the skin, into the blood stream, and on to the liver and/or kidneys. Most of the solvents are poisons.
    • PCB: PCBs were used as dielectric filler liquids in some older types of electrical equipment such as transformers, switchgear, capacitors and motors. You should assume that any capacitor or oil filled transformer manufactured before 1976 may contains PCBs unless you have information to the contrary.
    Be very cautious when you have risk to get into contact with the material listed above. Use necessary safety measures to avoid the dangers.

    Safety information

      Electrical safety

      Different currents and voltage have different effect to human being. Generally the current is what determines the danger to human. The used voltage with some other things (for example skin resistance) generally determines what is dangerous and what not. Generally the AC voltage in 40..50 Hz is very dangerous to human. A current that is less that 10 mA is not dangerous to most people. Alternating current (AC) in range of 70..110 mA and direct current (DC) in the range of 200..250 mA is considered to be very dangerous and lethal if it goes through the chest (where the heart is). The impedance of muman from one hand to hand is generally in the rnage of 600..6000 ohms depending on the skin moisture level and the amount of current flowing. Voltages below 20V can be considered safe to touch (the current does not exceed 10 mA in normal conditions). If the skin is dry, voltages up to aroun 80V do not cause over 30 mA current. There is a popular misconception that steady DC is worst due to its supposed ability to cause muscles to stay contracted. This is largely untrue, and AC actually sometimes causes this. AC of power line frequencies is also more capable of disturbing your heart rhythms than steady DC or AC of higher frequencies.

      Electrical power distribution system design is a compromise between safety and cost. Much of the world considers 220 V (220-240V) to be safe enough for standard residential outlets and lighting.Within the European Community the mains voltage is currently 230V +10/-6% (50Hz) between the LIVE and the NEUTRAL terminals, together with a separate protective EARTH terminal. When this high voltage is developed across the human body it could gives rise to a fatal electric shock. Therefore you MUST NOT under any circumstances simultaneously touch both the LIVE and the NEUTRAL terminals or you are very likely to die. Those countries which use 120V considered that 220V to be to dangerous for most residental uses. For example USA, Canada and many other countris have selected 120V AC. This 120V AC voltage is still high enough to be able to cause fatal electric shock if you touch both live and neutral wires at the same time.

      Remember that electric shocks can be fatal, even for voltages of 50 V, and that most of the resistance of the body is in the skin, so do not handle electrical apparatus with wet or even damp hands. Electricity kills a great many people worldwide every year. A current of 50mA (barely enough to make a low wattage lamp even glow) is sufficient to send your heart into a state called "ventricular fibrillation", where the heart muscles are all working out of synchronisation with each other. Little or no blood is pumped, and you will die within about 3 minutes unless help is immediately at hand. To avoid this kind of things to happen, the electrical installations and devices should be built in such way that people don't come in touch with the dangerous voltages. Different safety measures and standard exist for this. Insulation and grounding are two recognized means of preventing injury during electrical equipment operation. Conductor insulation may be provided by placing nonconductive material such as plastic around the conductor. Grounding may be achieved through the use of a direct connection to a known ground such as a metal cold water pipe.

      The sole purpose of a safety ground in electrical wiring is to protect against hazardous fault currents - if there can be no fault than a ground is never needed. In theory the safest electrical supply is one that is totally isolated fromits environment. In such a case you can safely connect yourself to anypart of the live circuit since there is no return path to carry a currentthrough your body. When you touch that isolated circuit, it is no longer isolated but is tied to ground at the point of contact, with yourbody as the potential fault current path. If a fault has previouslyoccured that caused another part of the circuit to be shorted to groundthen a return path will already exist, you will complete the circuit and acurrent will pass through your body. Whether the effect will be negligible, painful or fatal will depend only upon the fault impedences,potential difference and the current capacity of the supply.

      Floating supplies are permissible in certain circumstances. For example in some places bathroom shaver sockets are isolatedor even use this system - but the supply is provided by a current limiting isolation transformer. Floating supply is also recommended for medical life-support equipment where risks to human life due to an interruption ofthe supply are dominant. Floating supply in form of safety isolation transformer is also used in electronics laboratories to isolate the electronics equipment being tested or repaired from the mains supply. There are totally floating safety isolating transformers that supply 120/230 volts floating with respect to ground. These are intended for use by test/service engineers working on live mains-supplied equipment. The term 'safety' is relative of course - whilst it is perfectly safe to connect yourself to any single point of such a floating circuit it won't give an iota of protection if you were to touch both live and neutral atthe same time! In other words they only give protection against injury to people who know what they are doing - two strikes and you're out! However an isolating transformer should only be used for a single piece of kit. The safety relies on the integrity of the isolation of the entire supply on the secondary side of the transformer. Hence you should always keep power leads as short as possible. Floating the supply doesn't automatically make it safe - it just increases the number of faults necessary to cause anaccident and the greater the size and complexity of the installation the greater the chance of isolation failure. There is one wiring methid that uses ungrounded power supply, it is called TT wiring. In TT wirign system you have to fit analarm that detects the first fault to earth & an RCD system to copewith any further faults to earth. You normally only bother with this system in very special situations.

      Leakage to 'ground' is a very common occurrence and can arise due to insulation failure, cable damage, water ingress, breakdown of capacitorsetc etc, all of which are particularly likely in a mobile, temporary installation with a large amount of equipment and huge quantities of cabling running over metal edges on a truck. It can also occurcapacitively - insulation acts as a dielectric and capacitance increases with area and so may become significant with large cable runs. Because of those risks, the normal electrical distribution safety is generally based on grounding. Most of the time, earthing everything in sight will work. Very occasionally, it doesn't. It depends on the detailed design of the earthing system.

      Sometimes the safety level is expanded with other safety devices. RCDs detect an imbalance in the live and neutral currents. 30mA is usual, asnot being life threatening. This is always indicative of a fault situation, butthe current may be going anywhere. In most cases you puff and bluster to your hearts content about the theoreticalsafety of a totally isolated power installation but the fact remains thatinsulation faults can and do occur and if, as a result, someone were to beinjured or electrocuted then you as the specifier, installer or user wouldbe morally, legally and financially liable.

      Operator Exposure safety details. Operators shall not be exposed to:

      • Energy levels of 240 VA or more.
      • Stored energy levels of 20 J or more.
      • Potentials in excess of 42.4 V peak (30 VRMS) or 60 VDC in dry areas.
      • Potentials in excess of 10 VAC or DC in wet areas.
      The operator(s) shall be protected from electrical and mechanical hazards by one or more of the following:
      • Enclosures, shields, and covers that require a tool to open.
      • Interlock switches on doors, shields, and ovens.
      • Grounded or insulated handles, levers, knobs, shields and covers that are touched held or actuated in normal use.
      Service personnel shall not be exposed to inadvertent contact with hazardous potentials or energy levels. All areas not defined as operator access areas that skilled service personnel must gain access to service or maintain the equipment. Here are some tips for good electrical safety:
      • All systems shall be installed as intended by manufacturer or compentent electrical contractor that knows the device to be installed, and always according local electrical codes.
      • Any electrical installation, materials, equipment or apparatus within a workplace must be so designed, constructed, installed, protected, maintained and tested as to minimise the risk of electrical shock or fire.
      • Electrical wall outlets should be free of cracks, breaks, or other obvious damage. Damaged outlets should be immediatly repaired.
      • Personnel should conduct periodic inspections of all equipment to ensure that all cords are free of wear and splices, and that the casing or insulating covering is free of cracks, holes, or other damage.
      • Any electrical equipment that is damaged, malfunctioning or shows signs of unusual, excessive heating or producing "burning" odors, should be pulled from service and submitted for repair by qualified personnel.
      • If equipment produces shock, no matter how small, it should be removed from service and immediately repaired by a qualified electrician before returning to service.
      • Avoid excess bending, stretching and kinking of electrical supply cords.
      • Overloading electrical circuits is extremely dangerous and should not be permitted at any time. Significant amounts of heat can be generated by electrical leads which may lead to fires; especially if the current rating for the lead is exceeded.
      • Ensure that the wire sizes of extension cords are capable of handling the load without heating. When using extension leads ensure that they are fully extended, not covered by mats, and not placed where they could be a tripping hazard. If extension cord is coiled or covered with mat, it's safe current carrying capacity can be seriously reduced.
      • All electrically operated appliances that are designed to be grounded shall be effectively grounded. Tools or appliances protected by an approved system of double insulation, or its equivalent, need not be grounded
      • All electrical equipment should bear the label of a nationally recognized testing laboratory to guarantee that they are constructed safely.
      • If the competent person decides the equipment is not safe to use, they must attach a durable tag warning not to use the equipment; the equipment must also be immediately withdrawn from use.
      • Properly installed residual current device / earth leakage protection increases safety in dangerous locations. Residual current device should be periodically tested. Correct selection of the type of earth leakage protection is also important to avoid an unacceptable level of circuit tripping by the devices.
      • It is important to ensure that all electrical extension leads are in good condition before they are used.
      • The risk associated with electrical installations in hazardous atmospheres created by flammable gases, vapours from flammable liquids or combustible dusts should be carefully considered. Electrical appliances should either be specially designed equipment or be excluded from hazardous locations.
      • Special circuit protection such as residual current devices (RCDs) or isolation transformers are required for specified electrical equipment in workshops, laboratories, construction sites and other outdoor areas.
      • Patient treatment areas such as medical and dental surgeries have particular requirements on electrical safety.
      • Electrical heating appliances are a common cause of fires. Where possible appliances should have thermostat control and thermal overload protection.
      • Where electrical installations, equipment or extension leads are liable to damage from vehicles, other machinery or heavy people traffic, they should be protected from physical damage by appropriate covers or barriers.
      • The use of multi-outlet power boards or cords can be potentially unsafe because of the potential for overloading, and inadequate protection of circuits. In hazardous or wet areas multi-outlet power boards should be secured in a safe position.
      • All flexible cords will have two layers of insulation throughout their length, and will show no signs of excessive ware or physical damage.
      • Cord sets intended to be permanently attached to an item of equipment will be securely clamped to that equipment (internally or externally).
      European standards are different from US standards because they are intended for use in different overall regimes. Often the concepts forsafety in US standards and European standards are simply different, andrely on differences in the surrounding environments for even similar products. Wiring, earthing, field terminations, power distribution schemes etc. are simply different, and are not under the control of one single organization who writes standards (there are many regional standards organizations, they more or less follow international IEE standards and create their own).

      When working with electronic devices (repairing etc.) switch then off and disconnect from the mains. When you need to test live circuits, use properly sheathed probes and power the device through protection device such as isolation transformer. When working with mains voltage or higher voltage, make sure that there is someone else in the room and that he or she knows what you are doing.

      In normal operation electronics devices are designed such that they are safe to use. The insulation inside electronics devices must be good enough to withstand the mains voltage and overvoltage links. Even though there is insulation, there is always some leakages and potential for failures. There are are different equipment classifications based on their construction:

      • Class I devices are designed to have grounded metal case, which keep the leakage out of reach and burns mains fuse if there is short circuit to case.
      • Class II equipment are designed to work without grounding. They have thicker insulation in wires and components connected to mains. Leakage current from Class II equipment is limited low so that it is safe to touch, and I think we don't have to care of electric shock too much when using correctly designed Class II equipment alone.
      When questioning safety from electrocution the current draw of device in question is typically not an issue. The amount of current through your body depends on Ohm's law.That is, the current in any path is the voltage divided by theresistance of your body along that path. So voltage is the thing here. Any 120 volt appliance can be lethal, regardless of its current draw, sinceyou can possibly be exposed to 120 volts. This applies to 230V equipment also, here the voltage is only higher. Of course, you are exposed tothat current if you stick your finger in an outlet, without any appliance. So the question is, how well is the equipment/installation made to avoid any fault that exposes you to the 120 or 230 volts.

      The severity of an electrical shock depends on both the electrical voltage and current you are subjected to. The probability of getting killed by an electric shock is determined by the current through your body. The level which isconsidered lethal is in the range of about 100 mA to several hundred mA fornormal healthy people with surface skin exposure. The worst range is generally considered to be 100 mA to 1 amp. This is based on guestimates for healthy relatively fit people. Young children, older people or those who are sick can be more susceptible. This is just the worst range, with currents even well outside this range in either direction having a significant chance of causing lethal ventricular fibrillation. The effect of electricity also depends on what route the electricity takes in your body. If it was across the chest or more pointedly, across theheart, then it has a high possibility to cause the heart to go into cardiac arrest. The current through the person is determined by the voltage across the body and the resistance due to body tissue, whether the contact area is wet orsweaty etc. For most people, most of the time simply touching 120 V for a short time is not lethal. So the mains voltage of 120 V in the US is certainly not lethal in most situations. It is possible to be electrocuted by 120v mains, that's for sure. It is possible to be injured severely by mains voltage, but usually 120V mains does not cause severe damages. But for safety reasons it is a very good idea to avoid touching the mains electricity, because there is always the possibity to get killed or get injures. It is better to be safe than "try your luck" of surviving the electrical shock. If one were really afraid of electrocution from any appliance in any setting, then a GFCI device on the circuit containingthe appliance wouldn't be a bad idea. The GFCI would detect a malfunction and shut down the circuit before the person using the appliance got zapped.

      This same safety basics apply to 230V AC also. This higher voltage is even more dangerous than 120V AC because of higher currents involved if you touch the wire. Touching an exposed 230V AC wire here is much more dangerous than touching 120V AC wire.

      Generally the leakage current below 0.5 mA is not considered dangerous. And the isolation from the mains wiring to equipment case should be at least few kilovolts. Here are some general values for maximum allowed leakage current and insulation specifications of some power supply types / devices:

      • Office devices (EN60950): Maximum leakage 250 microamperes, 3000V insulation rating on test (60 seconds)
      • Medical types B and BF (EN60601): Maximum leakage 100 microamperes, 4000V voltage rating with 60 second test
      • Medical type CF (EN60601): Maximum leakage 10 microamperes, 4000V voltage rating with 60 second test
      Here are some general definitions considering electrical safety (from IEC 60950 / EN 60950 glossary):
      • Basic Insulation: Insulation to provide basic protection against electric shock. The standard defines levels of insulation required in terms of constructional requirements (creepage and clearance distances) and electrical requirements (compliance with electric strength tests) . Basic insulation is considered to be shorted under single fault conditions. The actual values required depend on the working voltage to which the insulation is subjected, as well as other factors.
      • Bounding Surface: The outer surface of the electrical enclosure, considered as though metal foil were pressed into contact with accessible surfaces of insulating equipment.
      • Class I: Equipment where protection against electric shock is achieved by using basic insulation, and also providing a means of connecting to the protective earthing conductor in the building wiring those conductive parts that are otherwise capable of assuming hazardous voltages if the Basic Insulation fails.
      • Class II: Equipment in which protection against electric shock does not rely on basic insulation only, but in which additional safety precautions, such as double insulation or reinforced insulation, are provided, there being no reliance on either protective earthing or installation conditions.
      • Clearance: The shortest distance between two conductive parts, or between a conductive part and the bounding surface of the equipment, measured through air.
      • Creepage Distance: The shortest path between two conductive parts, or between a conductive part and the bounding surface of the equipment, measured along the surface of the insulation.
      • Double Insulation: Insulation comprising both basic insulation and supplementary insulation.
      • Functional Insulation: Insulation needed for the correct operation of the equipment.
      • Hazardous Energy Level: A stored energy level of 20J or more, or an available continuous power level of 240 VA or more, at a potential of 2V or more.
      • Hazardous Voltage: A voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does not meet the requirements for either a Limited Current Circuit or a TNV Circuit.
      • Limited Current Circuit: A circuit which is so designed and protected that , under both normal conditions and a likely fault condition, the current which can be drawn is not hazardous.
      • Primary Circuit: An internal circuit which is directly connected to the external supply mains or other equivalent source (such as motor-generator set) which supplies electric power.
      • Reinforced Insulation: A single insulation system which provides a degree of protection against electric shock equivalent to double insulation under the conditions specified in this standard.
      • Safety Critical: A component which affects the safety of the equipment. All components in primary circuitry are safety critical. Other components which protect the equipment under normal and fault conditions, such as thermal switches, optocouplers, etc. are also safety critical.
      • Secondary Circuit: A circuit which has no direct connection to primary power and derives its power from a transformer, converter or equivalent isolation device, or from a battery.
      • SELV Circuit (Safety Extra Low Voltage): A secondary circuit which is so designed and protected that, under normal and single fault conditions, its voltages do not exceed a safe value (definatley lower than 42.4V peak or 60V d.c).
      • Supplementary Insulation: Independent insulation applied in addition to basic insulation in order to ensure protection against electric shock in the event of failure of the basic insulation.
      • Telecommunication Network: A metallically terminated transmission medium intended for communication between equipments that may be located in separate buildings, excluding mains electrical network, TV distribution systems using cable and SELV circuits connecting units of data processing equipment.
      • TNV Circuit: A circuit in the equipment to which the accessible area of contact is limited and that is so designed and protected that, under normal operating and single fault conditions, the voltages do not exceed specifying limiting values.
      • TNV-1 Circuit: A TNV circuit whose normal operating voltages do not exceed the limits for a SELV circuit under normal operating conditions and on which overvoltages from telecommunication networks are possible.
      • TNV-2 Circuit: This is a TNV circuit whose normal operating voltages exceed the limits for a SELV circuit under normal operating conditions. These circuits are not subject to overvoltages from telecommunication networks.
      • TNV-3 Circuit: This is a TNV circuit whose normal operating voltages exceed the limits for a SELV circuit under normal operating conditions. Overvoltages from telecommunication networks are possible for TNV-3 circuits.
      • Touch Current: Electric current through a human body when it touches one or more accessible parts. (Touch current was previously included in the term 'leakage current')
      Some other related terms from other standards:
      • Insulation resistance: Electrical resistance measured by applying a DC voltage of 500 V between two elements of a relay that are insulated from one another.
      • Creepage distance: Shortest distance on the surface of an insulating material between two conductive elements. [Source: IEC 664-1]
      • Tracking resistance Evaluation of insulating materials by determinating their creepage distance formation (by dripping a watery solution onto a horizontal surface so that it leads to electrolytic conducting), specified by the so-called "comparative number of creepage formation" (CTI) according to IEC 112. [Source: IEC 664-1, mod.]
      • Clearance distance: Shortest distance in air between two conductive elements. [Source: IEC 664-1]
      • Impulse form: The impulse form is characterized by the following values: voltage amplitude (e.g. 1.5 kV), rise time T1 (e.g. 1.2 ?s) and fall time T2 (e.g. 50 ?s
      • Insulation according to IEC 664 / VDE 0110 (1/89): Data for insulation coordination requires values for rated voltage, pollution degree and overvoltage category.
      • Insulation distance: The distance that needs to be insulated between two conductors.
      • Insulation group: Insulation group is the classification of equipment according to environmental and operating conditions and takes into account the reduction of insulation of equipment due to environmental effects at the site, increases in voltage that result from activities in the plant or in the atmosphere and direct results of insulation malfunction depending on short-circuit power.
      • Insulation distance: The distance that needs to be insulated between two conductors.
      • Overvoltage category: Classification of electrical equipment to the overvoltage to be expected.
      • Pollution degree: Classification of the pollution from external materials that affect the insulation.
      • Rated voltage: The voltage value above which the creepage distance is measured.
      • Surge voltage: Amplitude of a voltage impulse of short duration with a specified impulse form and polarity that is applied to test insulation paths in device/component. This proves that the device/component (for example relay) will withstand very high overvoltages for very short periods.
      • Test voltage (Dielectric test voltage AC): Voltage (effective value in AC voltage) that is applied between elements that are insulated from one another in the voltage test.
      • Voltage withstand test: A short-circuit fault in a circuit breaker creates an electrical arc in the device and subsequently results in high temperature and pressure. This test measures the insulating capability of a circuit breaker's components when twice the rated voltage plus 1,000 V is applied.
      Internaltiona Electrotechnical Commission (IEC) specified overvoltage categories:
      • Cat I: Electric devices (electric equipment, low energy equipment with transient limiting protection) (test for 600V working voltage: 2500V peak impulse, 30 ohms source, 20 repetitions)
      • Cat II: Appliances, PCs, TVs (outlets and long branch circuits, all outlets more than 10 meters from Category III source, all outlets at more than 20 meters from category IV source) (test for 600V working voltage: 4000V peak impulse, 12 ohms source, 20 repetitions)
      • Cat III: MC panels etc. (feeders and short branch circuits, distribution panel devices, heavy appliance outlets with "short" connection to service entrance) (test for 600V working voltage: 6000V peak impulse, 2 ohms source, 20 repetitions)
      • Cat IV: (outside and service entrance, service drop from pole to building, run between meter and panel, overhead line to detached building, underground line to well pump) (test for 600V working voltage: 8000V peak impulse, 2 ohms source, 20 repetitions)
      In those overvoltage categories the idea is the following: As you move close to the power source (higher category number), a higher level of protection is required. Demarcation between Installation Categories III and IV is arbitarily taken to be at the meter or at the mains disconnect (according ANSI/NNPA 10-1990, article 230-70) for low voltage service. If service is provided to user at high voltage, the demarcation between Installation Categories III and IV is at the secondary of the service transformer. Within each category you will also find a voltage rating. The higher the voltage rating, the higher the transient withstand rating. However, it is wrong to use voltage rating as the only criterion, and assume that a CAT II-1000V rated meter is superior to a CAT III-600V meter.

      Electrical safety cannot be over emphasised. When working with electricity, make sure that you find out the legal requirements in your country, and don't do anything that places you at risk - either from electrocution or legal liability. Neither is likely to be a pleasant experience. When working with eldctrical wiring or electronics circuits with dangerous voltages in them, working with them sould be done with them when the power on those devices is disconnected (exception to this are some special operations tha can only be done when those are powered up, and a special precautions and care shpuld be taken when performing those).

      When working with electrical wiring, the power should be cut out by removing a fuse and/or turning of electrical palel main switch off. When you turn th epower of for someone to work with electrical wiring, the switches/breakers should be locked out and marked that there is work in progress. Lock out devices are made for pretty much every breaker made to physically lock it out. In addition to this in some application the wires that needs to be worked with are grounded (especially in application where high voltages are present). There is no guessing when it comes to your life or others that may come in contact. If you are working on the wiring of a circuit (not just connecting alantern or adjusting one), in repairing it, you should use a lock-out/tag-out system. Turn off the breaker(s) that affect the circuit and using aproper lock device with a key that only you have, lock it and tag it withyour name, date and reason why it is locked out. This guarantees that ne can randomly turn it back on without your knowledge since they would have to get the keyfrom you. I which case, YOU are the only one that should be the one to re-energize that circuit. You are then the one responsible for whether or not the circuit is safe to reenergize.

      When working with electrical system you should consider doing risk assessment (in many countries there are legal requirements for this to guarantee workplace safety). The accepted best practice is for people with relevant experience andtraining in risk assessment to carry them out. Risk assessments are generally used to justify the safety related decision. There are many situations in the workplace that are perfectly 'legal' but might still need attention from a health and safety viewpoint.

      When voltages get higher than normal mains voltages, new extra safety things needs to be considered. Alternating current with a voltage potential greater than 550 volts can puncture the skin and result in immediate contact with the inner body resistance. A shock from greater than 600 volts almost always will result in very dangerous current levels. The most severe result of an electric shock is death. When voltages go even higher, new dangers enter to the picture. Electrical equipment operated over 10 kV in a vacuum may produce x rays that can penetrate the vacuum enclosure.

      The frequency of voltage has some effect how it affect human. At 60 Hertz, humans are more than six times as sensitive to alternating current than at 5000 Hertz. This sensitivity decreases further still as frequency increases. Above 100 to 200 KHz, sensations change from tingling to warmth, although serious burns can occur from higher radio-frequency energy. At much higher frequencies (e.g., above 1 MHz), the body again becomes sensitive to the effects of an alternating electric current, contact with a conductor is no longer necessary and energy is transferred to the body by means of electromagnetic radiation (EMR).

      Be careful whatever you do with electricity. 'Carelessness' is a the majority cause of accidents. Since electrocution is permanent it only takes one unlucky instance of carelessness in an entire career to terminate your contract!

    Electrostatic Discharge (ESD) information

    Static electricity is defined as an electrical charge caused by an imbalance of electrons on the surface of a material. To many people, static electricity is little more than the shock experienced when touching a metal doorknob after walking across a carpeted room or sliding across a car seat. In ordinary circumstances, static electricity and ESD are little more than an annoyance. However, in an increasingly technological age, the familiar static shock we receive when walking across a carpet can be costly or dangerous.his same static discharge can ignite flammable mixtures and damage electronic components. Static electricity can attract contaminants in clean environments or cause products to stick together.

    Environmental conditions have some effect on ESD problems. The lower the humidity, the higher the likelihood for ESD problems. Humidity helps because the moisture reduces the surface impedances, allowing charges to recombine at a faster rate. As a result, it's more difficult to develop the high voltage necessary for an ESD breakdown. In fact, studies have shown that at greater than 50% humidity, it's difficult for humans to exceed about 2000V. At 5% humidity, that level can reach 15,000V or more. Anything less than 20% humidity should cause you to suspect ESD. The high voltages are also felt by the people when they touch something grounded (the threshold of human feeling is about 2000 to 3000V). Humidity doesn't really control ESD, it just prevents high-voltage levels from occurring in the first place. Even with high humidity, though, you can still have problems.

    Static dissipative materials also provide a low surface impedance on materials such as countertops or packing material. This avoids high voltages to build up.

    Static electricity has been a serious industrial problem for centuries. The age of electronics brought with it new problems associated with static electricity and electrostatic discharge. And, as electronic devices became faster and smaller, their sensitivity to ESD increased. Today, ESD impacts productivity and product reliability in virtually every aspect of today's electronics environment. The cost of ESD-damaged electronic devices is usually very high. The cost of damaged devices themselves ranges from only a few cents for a simple diode to several hundred dollars for complex hybrids. When associated costs of repair and rework, shipping, labor, and overhead are included, clearly the opportunities exist for significant improvements.

    An ESD event is characterized by a very slow buildup of energy (often in the tens of seconds), followed by a very rapid breakdown (typically in the nanoseconds or even picoseconds). This fast breakdown causes many EMI problems in modern electronic equipment. ESD is a very fast transient. Two parameters are important: peak level and rate of change (dI/dt). Peak currents can exceed tens of amps, and rise times are in the nanosecond range. Due to this high speed/high frequency, ESD energy can damage circuits, bounce grounds, and even cause upsets through electromagnetic coupling. In the EMI world, you often convert rise times to an equivalent EMI frequency, where F=1/(p tr), where tr=rise time. With a typical 1-nsec rise time, the equivalent ESD frequency is more than 300 MHz. This is no longer static electricity, and VHF (not DC) design techniques it requires. The typical circuit for ESD (electrostatic discharge) testing is a 150 pF capacitor charged to test voltage (several kilovolts) and discharged to the tested device through 330 ohm resistor.

    You have two choices when dealing with ESD: prevent it or deal with it. Prevention is the primary strategy in manufacturing. Controlling electrostatic discharge begins with understanding how electrostatic charge occurs in the first place. Static electricity is measured in coulombs. Commonly, however, we speak of the electrostatic potential on an object, which is expressed as voltage (usually in the range from few hundred volts to 30 kV).

    The first Principle is to design products and assemblies to be as immune as reasonable from the effects of ESD. This involves such steps as using less static sensitive devices or providing appropriate input protection on devices, boards, assemblies, and equipment. IEC-801 standard covers protection of electronic device against ESD. Then define the level of control needed in your environment. Identify and define the electrostatic protected areas (EPA). These are the areas in which you will be handling sensitive parts and the areas in which you will need to bond or electrically connect all conductive and dissipative materials, including personnel, to a known ground. Also eliminate or reduce the generation and accumulation of electrostatic charge in the first place and safely dissipate or neutralize those electrostatic charges that do occur. Proper grounding and the use of conductive or dissipative materials play major roles.

    In electronics workshops when people are working with electronics devices special antistatic straps (grounding straps) and mats are used to control then environment so that no considerable electrostic charges can build up. Grounding straps, either of the sort included with such amat or sold separately (the sort that have a wrist band andthen connecto somehow to a ground point) SHOULD have a fairly high resistance in series with the ground connection - about 1Mohms is common. The idea is to drain off static chargefrom the wearer WITHOUT adding a safety hazard - so you put a high enough resistance in the path such that no appreciable current would flow if you contact, say, the AC line. Always place a current limiting resistor in series with you ground wire to limite the current passing through your body if you accidently touch a hot wire. Always connect it to your wrist, and never to you ankle. Many electronics laboratories have testers to test the effectiveness of the grounding practices used. The testing range is ypically so that around 500 kohms to 10 Mohms is considered as working ESD protection. Anything less than 500 kohms is a safety hazard and anythign more than 10 Mohms is considered as not adequate grounding to avoid ESD problems.

    You are not the only thing that needs to be discharged. It's also equally important to discharge any static charges from the circuit that you're working on, so its also a good idea to have a second grounding strap, or grounded anti-static mat, in contact withthe circuit assembly you're working on. Never handle a PCB assembly without grounding off any charge that one may have accumulated. Always touch the bench first, even if strapped up. The skin on the wrist is a lot drier than the hand. Wrist straps do not always make as good a connection to the body as they need to. A good rule of thumb is to ALWAYS touch the antistatic mat (or other similar connected grounding point) when you walk to to an ESD workstation. In that way, you, the mat, and anything on the mat (PCBassemblies)are at equipotential. It's important to elmininate ESD, but more important to avoid becoming electrocuted in the process. Always be sure that there is a current limiting resistor in your grounding path for ESD. It's also an important safety precaution to NEVER connect any ground strap to your ankle, becuase it's your hands that generally run the risk of contacting a dangerous voltage level. Under no circum stance do youwant any current path to run through your body trunk for obviousreasons.

    A proper "ESD workstation" would be comprised of many or even all of the following:

    • A grounded ESD work surface where said ground line contains the proper 1M ohm dropping resistor.
    • Your PCB assembly can be considered safe while on this mat.
    • A grounding strap for your wrist to make a constant contact with the ground mat or other grounded element on the bench will keep you balanced. This strap should also have a 1M Ohm resistor in series with it to the ground point.
    • You should also have either only cotton clothes on, or you should wear an ESD vest, or smock. Never wear poly fabrics when working on electronic assemblies.
    • Heal straps are a good thing, but are not required, provided you remember to constantly ground yourself at the mat. You should also never pick up an assembly from the bench without the wrist strap in your grasp or on your wrist.
    • The ground should be earth via nearby ground rod, but electrical ground is also suitable, though not ideal.
    You can buy the necessary parts to build such "ESD workstation" from many companies whick sell tools for electronics work.

    ESD is a major issue with elecronics device interface design and can be difficult to handle well. The important thing to remember is that ESD currentscan be very high at the instant of discharge, and can disrupt signals and grounds throughout a circuit if they are allowed to pass through (or near)the circuit. Many people try to use brute-force methods to channel the currents to ground, and assign all sorts of mystery to the ESD problem - and usually fail to resolve it. It is better to stop and consider the situationin a logical fashion, and then allow the usual rules of circuit design todictate the methods to use. A human being crossing a floor accumulates a charge. The human appears as acapacitor in series with a resistor, one end of which is connected to thefloor/building/earth. With the capacitor charged to tens of thousands of volts. When this human being touches the electronics device interface, the energy in the capacitor will discharge through the ground contacts, data contact, and whatever circuitry is connected to them, in an attempt to reach ground. Analyze what what happens on the route to ground.

    There are several standards that define human body model ESD protection and test methods, such as IEC 61000-4-2 (EN61000-4-2), EN50022, MIL-STD-883 Method 3015.7 etc., each with a different emphasis.

    For example, IEC 61000-4-2 requires the use of an ESD "gun," which allows testing with either contact discharge or air discharge. Contact discharge requires physical contact between the gun and the I/O pin before test voltage is applied by a switch internal to the gun. Air discharge requires the gun to be charged with test voltage before it contacts the I/O pin (produces a spark at some critical distance from the test unit). ESD produced by air discharge resembles real ESD events, but However, like real ESD, the air-discharge variety is not readily duplicated. Therefore, attesting to the general importance of repeatability in testing, contact discharge of IEC 61000-4-2 is recommended. The standards call for at least 10 discharges at each test level. According to IEC 61000-4-2, the severity levels range from 2kV to 15kV (air discharge), depending on the environment. For contact discharge the highest level is 8kV.

    Electromagnetic Compatibility (EMC)

      General EMC introduction

      EMC is the ability of an electric device to functionsatisfactory in its electromagnetic environment (immunity)without introducing intolerable electromagnetic disturbancesto that environment (emissions) or to other devices there in.Most products today have microprocessors used to control its functions and to enable data to be sent to associated peripheral devices and beyond, by, for example, connections to local area networks and telecommunications lines. These products generally fall into a class of products called information technology equipment (ITE) and are subject to mandatory RF emission limits in most countries, and to mandatory immunity requirements for specific regions of the world such as the European Union.There are many both regional and international standards related to EMC. Here are some commonly seen:

      • CISPR Publication 22 (Emission limits and measurement methods)
      • CISPR 24 (Immunity limits and measurement methods)
      Historically, definitions of environments with "abnormally high ambient electromagnetic interference" have been vague. The field strength guideline most commonly accepted as the threshold for high EMI environments is 3 Volts/meter4 (V/m). Usually interference levels greater than 3 V/m typically exceed the noise immunity levels of digital devices and are above the sensitivities of analog devices. Measured Field Strength of some devices (as example only,data from Siemeon UTP Cabling and the Effects of EMI paper):
      • Electric hand drill 1-2 V/m
      • Radio transceiver set 3-18 V/m ("walkie-talkie" radio 154 MHz)
      • Fluorescent light 1-3 V/m
      • Microwave oven 1-3 V/m
      Those are just examples of interference that can be present near those specified equipment.

      Designing for EMC in mind and solving problems

      There are three essential elements to any EMC problem. There must be a source of an electromagnetic phenomenon, a receptor (or victim) that cannot function properly due to the electromagnetic phenomenon, and a path between them that allows the source to interfere with the receptor. Each of these three elements must be present although they may not be readily identified in every situation. Electromagnetic compatibility problems are generally solved by identifying at least two of these elements and eliminating (or attenuating) one of them. Electromagnetic interference may be produced from a number of sources within electrical and electronic equipment, including components on PCBs such as microprocessor clocks or relays, or by the equipment's power supply. Other potential sources of electromagnetic compatibility problems include radio transmitters, power lines, electronic circuits, lightning, lamp dimmers, electric motors, arc welders, solar flares and just about anything that utilizes or creates electromagnetic energy. Potential receptors include radio receivers, electronic circuits, appliances, people, and just about anything that utilizes or can detect electromagnetic energy. Methods of coupling electromagnetic energy from a source to a receptor fall into one of four categories.

      • 1. Conducted (electric current)
      • 2. Inductively coupled (magnetic field)
      • 3. Capacitively coupled (electric field)
      • 4. Radiated (electromagnetic field)
      Coupling paths often utilize a complex combination of these methods making the path difficult to identify even when the source and receptor are known. There may be multiple coupling paths and steps taken to attenuate one path may enhance another. The interference may then be radiated from the equipment via a number of different paths, depending on the frequency of that interference. At high frequencies tracks on PCBs may well radiate directly. At lower frequencies interference may well be coupled from the equipment via connecting leads, such as signal or mains cables, as conducted emissions.These conducted emissions may well be radiated at a different location as further radiated emissions. The transition between radiated and conducted emissions is generally assumed to be around 30 MHz - conducted emissions dominating below this figure, and radiated emissions above. One very large source of EMC problems are related to the cabling. The signals entering the cablings should be properlyfiltered and cabling should be suitable for the application(quite often shielded). Even with quality cable installed EMC may be a problem if interfering circuits are not properly enclosed. The design of enclosures and subsequent testing is usually a costly iterative process. The reason for iterative testing usually comes from the fact that the enclosure needs to be such that it shields well enough, but is not too expensive.For shielding to be effective it is essential that all apertures and holes are designed to minimise electromagnetic radiation. A good rule of thumb is to keep holes apertures and seams less than 1/20th of a wavelength in size. For example to mitigate up to 100MHz (wavelength of 3m) openings must be less than 150mm and this includes the front door of the cabinet. Non-removable joints and seams may be coated with conductive paint. Close spacing of bolts with metal to metal contact is advised and doors may be fitted with EMC gaskets (contact fingers).Cables are a common source of noise exiting from the devices. A proper shielding of cables and filtering of signals getting to those cables help to avoid EMC problem. Usually when the devices operate at the high frequencies, suitable EMI/RFI filters ar needed to stop the high frequencies inside the equipment to get out of it through the cables. Passive EMI/RFI Filters consist of inductors, capacitors and in some cases resistors in selected combinations, designed to pass or reject selected frequencies. In some cases ferrite beads are needed in the cables.The function of a ferrite bead on a cable is to help ensurethat there is no "common mode" current flow (i.e., a netcurrent in one direction only) along that cable. Cableradiation is primarily due to such currents, as they createfields which are not cancelled by opposing fields from acurrent in the opposite direction. Ideally, cables carryinghigh-frequency signals would be perfectly "balanced" -any "outward" flow of current is exactly matched by a"return" current following the same physical path, resultingin completely cancelled fields. A ferrite bead increasesthe impedance seen by unbalanced or "common mode"currents (by adding inductance to that path); balancedcurrents see nothing at all, since both the "outbound" and"return" currents pass through the ferrite. (And if thecurrents are already perfectly balanced, the addition ofa ferrite "bead" or "core" will have absolutely no effectbeyond making the cable assembly heavier...:-)) In short,the ferrite does not usually act by "shielding" or absorbing theradiation. In fact there are some bead materials are specifically designed to be lossy and these types are quite often used for common mode supression purposes. In practice, depending upon frequency ranges, power levels, etc... thelossy beads will outperform the "lossless" ones. However, it's still not working just by "absorbing" any RF noise in the vicinity.Placing a ferrite on a cable will reduceRF pick-up by the cable only to the degree to which theRF generates common-mode noise. The common mode signals on the cable generallyresult from the "return" current finding another path back tothe source. For example, a common source of RFI inPC systems is the video cable - when a part of the videoreturn current makes it back to the PC over the safetyground path or some other cable's shield, rather than viathe video cable's intended return path. In this case, addinga ferrite reduces the "attractiveness" of that path for thecurrents in question, as it appears as a series impedancein any such path.In the case of RF being induced on a cable, common-modeinduced current results from both the "outbound" and "return"conductors seeing identical ambient fields. Differential currents, though, can also be induced in cablesvia fields coupling in through any open "loop area" betweenthe two conductors, and again ferrites around BOTHconductors will have no effect on these. (And it is oftenthe case that the equipment in question will be far moresensitive to differential-mode noise vs. common-mode.)Ferrite beads are usually a good quick radiated-noise fix, but it is not generally considered ferrites to be a particularlyworthwhile cure for many RF-susceptibility problems.

      EMC testing information

      EMC testing can be made in many ways. Techniques are available to enable both conducted and radiated emissions measurements to be made. Those both types of emissions need to be tested in EMC testing.

      For radiated emissions the most commonly used measurement techniques are antenna-based measurements in screened rooms, anechoic chambers, open area test sites and GTEM cells. Conducted emissions are measured via a line impedance stabilising network or using a ferrite (absorption) current clamp.

      Open field measurements involve placing EUTs on a non-metallic turntable in the calibrated green field test site and measuring the electric field for various orientations to the antenna, and with vertical and horizontal wave polarisations over the frequency range of perhaps 30 MHz - 1 GHz. The EUT to antenna distance is set to 3, 10 or 30 metres to place the receiving antenna well into the far field for the emissions. An open area test site (OATS), as its name suggests, is a large, flat, outdoor open area, free from overhead wires, and sufficiently large to allow adequate separation between antenna, test unit, and nearby reflecting structures - including the test equipment housing. Open area or open field test sites are specified by most regulatory authorities, such as CISPR (CISPR 16), for radiated emissions testing of domestic and commercial electronic equipment. They can, however, only be used for emission testing. The major disadvantage of open-field test sites is their lack of isolation from the electromagnetic ambient, which can on some sites preclude the use of some frequencies (usually at broadcast bands). For this reason OATS must be calibrated before testing in order to account for the site's electromagnetic ambient. The major advantage of an open-field test site is its accuracy and repeatability when compared to an unlined or even semi-anechoic screened chamber due to its complete absence of reflections (except from the ground plane).

      Unlined screened rooms can be, and certainly are, used for radiated emissions measurements, although such tests would comply with no standards because a multitude of reflection paths via the floor, walls and ceiling can effect the measurement results considerably. The test cases where equipment are passing or failing by a wide margin can usually made quite well with this kind of room. You can for example use this type of room for your pre-compliance testing before sending your equipment to a test facility for the final tests.

      A very popular alternative to open area test sites radiated emissions measurements is the anechoic chamber. The big advantages of anechoic chambers for emissions measurements are that the facility is indoors and shielded from external noises. But the the anechoic chambers have their limitations: size constraints and limits of RF performance. At UHF frequencies and above a chamber can be made anechoic - the depth of the absorber on the walls limits the lowest anechoic frequency and few chambers can be considered anechoic below 100 MHz. The lack of anechoic performance below 100 MHz results in resonances within the chambers and leads to measurement uncertainties, negating the chamber's advantage of negligible electromagnetic ambient. The absorptive material (expensive stuff) is strictly to reduce(hopefully eliminate) reflections within the chamber. External RF is kept out simply by making the chamber asealed conductive enclosure - which is done easily enoughvia sheet metal, wire mesh/screen, and gasketing.

      GTEM cells are special devices that can be used for radiated susceptibility measurements and for radiated emissions measurements. GTEM cell is a specially designed screened measurement enclosure with HF absorber and special signal feeding/receiving wire. The susceptibility measurements are made by feeding radio frequency signals (from some form of radio transmitter) to the GTEM sell feeding point. Emissions are measured at the feeding point of the GTEM cell, at each frequency in the range, and for orthogonal arrangements of the EUT. The measurements are then converted by means of a "GTEM antenna factor" into a field intensity value. GTEM cells can be generally used for the frequency range 30 MHz to 1 GHz.

      An absorbing ferrite clamp consists of a current transformer and a further series of ferrite rings which act as a power absorber and impedance stabiliser. The ferrite clamp is intended to allow the measurement of the interference power present on the mains cable of equipment. Again, in a similar way to RF current probes, ferrite clamps can be hinged open to allow insertion of the mains cable. The ferrite absorbers behind the current transformer attenuate reflections, and absorb interference, isolating the measurement from noise on the mains supply itself. The construction and use of a ferrite clamp is specified in the standard CISPR 16.

      A LISN, or line impedance stabilising network, also known as an artificial mains network, allows conducted voltage emissions tests to be made on the mains connections of an EUT. Such a device isolates the EUT from interference on the mains supply and provides a known RF impedance for coupling to a measuring instrument. CISPR 16 includes a design of LISN intended primarily for use up to 30 MHz, although other designs do exist (also for higer frequencies).

      EMC is a hard topic to cover well. However, almost the whole EMC business is on a very shaky base, due topractical limitations and complexities that are inherent in the subject.

      Examples of tests to current standards

      • EN 55011 Interference emission from industrial, scientific and medical devices (ISM appliances)
      • EN 55013 Interference emission from radio receivers and consumer electronic appliances
      • EN 55020 Interference immunity of radio receivers and consumer electronic appliances
      • EN 55014-1 Interference emission from household appliances
      • EN 55014-2 Interference immunity of household appliances
      • EN 55015 Interference emission from electric lighting equipment
      • EN 61547 Interference immunity of electric lighting equipment
      • EN 55022 Interference emission from information technology equipment (IT appliances)
      • EN 55024 Interference immunity of information technology equipment (IT appliances)
      • EN 61000-4-2 Interference immunity to electrostatic discharge (ESD)
      • EN 61000-4-3 Interference immunity to electromagnetic fields
      • EN 61000-4-4 Interference immunity to fast transient orders of interference (burst)
      • EN 61000-4-5 Interference immunity to surge voltage
      • EN 61000-4-6 Interference immunity to conducted orders of interference induced by high frequency fields
      • EN 61000-4-8 Interference immunity to magnetic fields with energy technology frequencies
      • EN 61000-4-11 Interference immunity to voltage drops, short-time interruptions and voltage fluctuations
      • EN 50081-1 Interference emission from appliances in the household area
      • EN 50081-2 Interference emission from appliances in the industrial area
      • EN 50082-1 Interference immunity of appliances in the household area
      • EN 50082-2 Interference immunity of appliances in the industrial area
      • EN 61000-6-2 Interference immunity of appliances in the industrial area
      • EN 61000-3-2 Reactions in electricity supply systems - harmonic oscillations
      • EN 61000-3-3 Reactions in electricity supply systems - voltage fluctuations
      • EN 60601-1-2 EMC medical electric appliances

      There is trend that the electrical noise is increasing in our environment and electronics needs to ne designed in such way that it work is noisy environment. ADSL and VDSL (broadband internet over ordinary telephone wires), low voltage lighting using "transformerless" power supplies, plug-top switch-mode power supplies, variable-speed motor drives used in domestic appliances to save energy, power line telecommunications (PLT), ultra-wideband (UWB) radar and radiocommunications are examples of the kinds of "noisy" low-cost electronic devices and systems likely to enjoy wide adoption over the next few years. There is a huge RFI noise caused by "ensembles" of many thousands of such cheap and cheerful interference sources, even if they all actually complied with the relevant emissions standards prevailing at the time they were taken into service and none were faulty.

      Handbooks

      • Understanding EMC Standards and specifications - Document collection introduces the standards and regulations associated with EMC protection, and provides detailed information to help you understand filter design and specifications. It will help you identify for your application the right specifications and type of filter.    Rate this link

      Computers

      • Dealing with Computer generated RFI/EMI - One of the most frustrating problems about using computers with radios, whether it be for controlling purposes or for decoding, is the amount of RFI generated by these machines. Most of the time, the RFI generated is enough to render certain bands useless and on other bands, it may drown out any weak signals and distort or interfere with signals that you want. The bad news is that, there is no way that I know of to completely remove the computer generated RFI in most situations. The good news is that there are definite steps that we can take to reduce the RFI to a very acceptable level and in some cases, it will almost disappear altogether. This document is a compilation of suggestions from various persons and some of the things I have tried with my own system when dealing with this problem. Many of the documents I have seen relate to situations involving transmitters and how not to generate them (RFI). This document is written from a receiving point of view.    Rate this link
      • Reducing Emissions - Many hardware-design engineers use signal-integrity-analysis software to check every trace on their boards for acceptable ringing, crosstalk, and delay. Often during this process, the termination resistors are changed to ensure that the proper voltage waveforms arrive at every receiver. Once the voltage waveforms are acceptable, the design process is complete. This process is good enough for signal integrity, but it's not good enough for EMI because most radiated-emissions problems depend more on signal currents than on signal voltages.    Rate this link

      Conducted emissions measuring

      Power Line Impedance Stabilization Networks (LISN) and absorbing clamps are intended for electromagnetic interference testing and certification of electronic products at an EMC test laboratory. Line Impedance Stabilization Networks (LISN) are specialized low pass filter networks used to measure common mode conducted emissions from power lines. Used to test for compliance testing requirements. During the conducted emissions tests, the LISN isolate the electrically powered equipment under test from the external power source, stabilize the line impedance and provide a 50 Ohm RF connection to measure EMI voltage generated by the equipment under test. The absorbing clamps also known as ferrite clamps are used for measuring radio noise power in lieu of radiated emissions measurements for certain restricted frequencies and for certain types of products.

      • EMI Testing Fundamentals: Radiated & Conducted EMI - The FCC regulations that outline the legal requirements relevant to permissible radiated and conducted EMI from electronic products are contained in Part 15, Subpart J of the Article 47 of the Code of Federal Regulations (CFR). These rules define the types of electronics products that are explicitly regulated, the maximum permitted EMI signal limits, the formal FCC product approval process, and legal penalties for noncompliance.    Rate this link
      • EMI Testing Fundamentals    Rate this link

    EU regulations and CE marking

    The CE Mark is a product certification mark that is placed on products compliant to the New Approach Directives of the European Union. The CE Mark is required for manufacturers (from anywhere in the world) wishing to sell their products into the European Union. The CE Mark proves to buyers that the product fulfills all the essential safety and environmental requirements as defined in the European Directives.

    The CE Marking Directive (93/68/EEC) was adopted on 07-22-1993. From the 1st January, 1996, all equipment containing electrical components or electronics need to be 'CE' labelled if they are for sale within the European Community or EFTA. A product should not be in the EU market unless it complies with whatever Directives are applicable. The 'CE' mark tells that the product fullfills the applicable directives (whatever they might be for a particular product). The CE Marking Directive marking directive defines the use of CE mark. Very many products must have CE mark to be legally sold within EU, but not all (and there are some products you are not allowed to put CE mark to). The CE Marking Directive gives a detailed description of the initials CE and any other marks specific to a particular directive and the ways conformity may be acquired. In return for fulfilling the CE Marking requirements, the manufacturer (or its agents) is able to market the product across the entire European market with only one approval procedure.

    For equipment manufactured in the EC, the manufacturers are responsible. For equipment imported into the EC, the importers are responsible.First you need to understand what 'CE marking' means. isn't, in itself, something you can 'meet'. Products marketed in Europe are subject to the requirements of certain European Directives, the Low Voltage Directive (on electrical safety),the EMC Directive, the Medical Devices Directive, the Machinery Directive and several others. Some of these invoke the CE Marking Directive, which requires the CE mark to be applied to the product, showing to Customs officers and regulatory authorities that the product may cross national boundaries and be legally offered for sale. CE mark was created to to ease restrictions oncommerce between EU member states by "leveling the playing field. "That is ALL that the CE mark is for.

    Labeling on products that bear the CE Mark or documentation accompanying such products should indicate the year in which the manufacturer affixed the CE Mark. If this date is absent, customs inspectors can assume that the importer or manufacturer represents the product as complying with all directives that apply to products of the appropriate class on the date of the customs inspection. The inspection can occur long after application of the CE Mark. So, manufacturers and importers of products whose documentation or labeling fails to indicate when the CE Mark was affixed might be responsible for some expensive retrofits or upgrades.

    The CE Mark means that an importer or a manufacturer declares that its products comply with the portions of the EU's Marking Directive that apply to products in a particular class. Ir says "Trust me." It also says "I (manufacturer or importer) promise I did adiligent effort ensure compliance, or you can legally beat me up." The responsibility for placing a CE mark on a product is that of the manufacturer, in case the product is manufactured in EEU. As soon as something is imported from outside of the EEU, only the "importer" (inside the EEU, naturally) is responsible for CE certification. His name and address have to be given on the CE certificate. After all, CE is only a self-certification, but it provides enough information to start legal action in case something goes wrong.

    Many products are "Self compliant", which simply means that any company can put apply the CE mark, if they're willing and able to support the claim. That's why most companies prefer to pay Notified or Competent Bodies to check their products that they are according the standards. In all cases, the company bears responsibility for applying the mark. The responsibility cannot be delegated to a third party. Reports from a third party can only support the company's Declaration of Conformity.

    In the case of RF equipment like radios, transceivers, etc. some of it is not "self compliant" and must be submitted to a Notified Body, who will ensure that the EUT complies. RTTE Directive applies only to products which communicate using radiated RF.If, per se, a unit falls into a category where by the same standard applies to all countries, testing to a "harmonised" standard could be sufficient.

    So in practice CE Mark indicates neither that any government or private body has tested the product nor that the product is designed or manufactured in accordance with any standards. For example, the CE mark can appear on products manufactured in facilities that do not comply with ISO 9000-series documents. Low voltage directive says that the manufacturer must have some sort of quality control system that makes sure that every manufactured device meets the directive and the technical specifications the product is claimed to have.

    There are no 'listing authorities' in Europe. There are independent test-houses that conduct their tests according to international standards are subject to strict by national accreditation services.

    Authorities in any European country who determine that a CE-marked product fails to comply with applicable directives can halt the sale or distribution of the product throughout the EEA. Moreo