Safety measures to be taken in electrical works

archdevil

Royal Member
Safety measures to be taken in electrical works
  1. All systems shall be installed as intended by manufacturer and according local electrical codes.
  2. 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.
  3. Electrical wall outlets should be free of cracks, breaks, or other obvious damage. Damaged outlets should be immediatly repaired.
  4. 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.
  5. 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.
  6. 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.
  7. Avoid excess bending, stretching and kinking of electrical supply cords.
  8. 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.
  9. 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.
  10. 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
  11. All electrical equipment should bear the label of a nationally recognized testing laboratory to guarantee that they are constructed safely.
  12. 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safe to use, they must attach a durable tag warning not to use the equipment; the equipment must also be immediately withdrawn from use.
  13. 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.
  14. It is important to ensure that all electrical extension leads are in good condition before they are used.
  15. 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.
  16. 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.
  17. Patient treatment areas such as medical and dental surgeries have particular requirements on electrical safety.
  18. Electrical heating appliances are a common cause of fires. Where possible appliances should have thermostat control and thermal overload protection.
  19. 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.
  20. 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.
  21. All flexible cords will have two layers of insulation throughout their length, and will show no signs of excessive ware or physical damage.
  22. Cord sets intended to be permanently attached to an item of equipment will be securely clamped to that equipment (internally or externally).
Wiring systems
Single phase power has the mains voltage (typically 120V AC or 230V AC depending on the country) between two wires: live and neutral. The frequency of AC voltage is 50 or 60 Hz depending on the country. Single-phase power is used in very many applications, for example to power all typical home electrical appliances. You get single-phase power from normal elecrical outlet in home. Distributing single-phase power takes two wires: live and neutral. In some cases an extra safety ground wires is used to provide increased user safety.

In three phase power system the generator the generates electricity produces three voltages. Each voltage rises and falls at the same frequency (50 Hz or 60 Hz depending on the country). However, the phases are offset from each other 120 degrees. Electrical utilities generate and transmit three-phase power. Commercial electrical generators of any size generate three-phase AC power. The 3-phase power leaves the generator and enters a transmission substation at the power plant. Three phase power is commonly found in industrial applications and electrical distribution. Three-phase electrical generation is very common and is a more efficient use of conductors than other systems. Three phase power is particularly useful in AC motors, where it can be used to generate a rotating magnetic field easily and efficiently. Practically all large electrical motors used in heavy industry use three phase power.

Three phase power distribution saves copper for the following reason: At the load end of the circuit the return legs of the three phase circuits can be coupled together at the neutral point, where the three currents sum to zero. This means that the currents can be carried using only three cables, rather than the six that would otherwise be needed. In practical applications the three phase power is wired either with only three phase wires or three phase wires plus neutral wire systems. In addition to those there shall be a separate safety ground wire in case of LT system.

Three phase 230V/400V is the standard way for three phase power distribution in Europe to homes. The ouput from mains transformer is Y-conneted. There is 230V AC from each phase to neutral and 400V AC from phase to phase. The normal 230V electrical outlets are wired between neutral and one phase. Large high power loads use all three phases (the individual loads in such equipment can be phase to neutral or phase to phase as needed).

Human sensitivity to electricity
A number of years ago an awareness and concern about the effects of power frequency EMFs arose. For a number of years it had been known that electrical workers that were in close proximity to very strong magnetic or electric fields sometimes "saw" flashing lights or patterns that were supposed to be due the action of these fields on the nervous system. This was obviously evidence of the fact that EMFs could have some direct effects on a human directly, but little attention was paid other than as a curiosity. Today the average home or office is literally full of field producing devices. While the jury is still out on the biological effects of these fields on the human body, there is still sufficient evidence, both observed and anecdotal, that may be significant. It might be wise to take at least some precautions to try to minimize the production of these fields in new designs, and to check existing equipment for the presence of EMFs.

Electric fields are not very strong in most parts of a house. High electric-field areas are found near TVs, computer monitors (including laptop computers), fluorescent lights, light dimmer controls, and improperly grounded equipment. Electric fields are measured in (V/m). Also the frequency of the field (Hz) is important.

Magnetic fields are much more common in the home than are electric fields. Most of the recent health concerns have been about magnetic fields. Any wire that carries an AC electrical current produces magnetic fields. However, two wires are required to carry power to an appliance, and if the two wires are bundled parallel and very close together, the magnetic field from one will exactly cancel the field from the other. Thus, an extension cord rarely produces much magnetic field. Electromagnetic fields are measured in Tesla (nT) or Gauss (G). Also the frequency of the field (Hz) is important.

Many experts nowadays agree there could a link between magnetic fields and some diseases. Laboratory studies have shown that electrosmog (electrical and magnetic fields) can affect living cells but it is unclear whether these effects are harmful. Some epidemiological studies have reported a possible link between electrosmog exposure and cancer. Other studies indicate that continuous exposure to levels as low as 2 Milligauss (mG) may be harmful. Current research is expected to provide more answers about potential health effects within the next few years (answers is there effect or not). There are some thoughts that magnetic fields from power lines could linked with cancer.

Protection devices
Many precautions are needed to make occurence of short circuits unlikely, because the very high currents caused by short circuit situation can cause lots of damage to electrical installation. Protective devices are needed to break short-circuit and overload currents.

One type of situation that wiring needs to be protected against is over current. The electrical wiring is rated for certain maximum current. If you try to pull more current through it, the wiring will heat considerably. When the wiring heats too much, it will cause the meltíng of cable insulation, cause fire if there is something flammable near cable and even melt the copper conductors in the cable. So protection is needed to guarantee that in case of something tries to pull too much current through mains wiring, this cannot happen for any long time until the fuse blows and stops the current. Fuses and circuit breakers protect nicely against over current.

Many people are familiar with a “short circuit,” which is a type of fault that occurs when two conductors of an electric circuit touch each other. The current flow caused by a short circuit is usually high and rapid and is quickly detected and halted by conventional circuit protective devices, such as fuses or circuit breakers.

Ground faults are one type of problem when the insulation fails. When mains power line connects directly to ground, its goal in life is to pump as much electricity as possible through the connection. If there is nothing to stop that, either the device or the wire in the wall will burst into flames in such a situation. A fuse is a simple device designed to overheat and burn out extremely rapidly in such a situation, thus stopping the current from flowing through the wire (thus stops the dangerous short circuit situation).

An arc fault is a high power discharge of electricity between two or more conductors. The arc faults of our concern occur in major electrical distribution systems where there is considerable current available. While a low power arc of a few amps may initiate an arc fault, a true arc fault will rapidly increase in current up to several hundred amps or even thousands of amps. A large arc fault can cause a large electrical switchboard to be reduced to an empty shell in a few seconds. This is caused by the fact that in this kind of short circuit situation there is very much power available from electrical distribution system, and this power will generate lots of heat, that will burn anything near (here withing the electrical switchboard). The chance of Arc Faults in electrical switchboards can be reduced by proper design.

In home wiring an arc of a hundred watts can set wallboard, carpet, cloth, wooden studs, etc on fire. This kind of arc can be caused by bad wiring (broken insulator in the wiring, bad wire terminations etc.) This kind of arc fault can be defined as an unintentional electrical discharge characterized by low and erratic current that may ignite combustible materials. The US Consumer Produce Safety Commission states "Problems in home wiring, like arcing and sparking, are associated with more than 40,000 home fires each year". An arc fault, however, is characterized by the low and erratic flow of electricity. Due to these types of characteristics, arc faults occurring in damaged electrical cords or cable can continue undetected by conventional circuit protective devices. This leads to hazardous situations such as igniting of nearby combustible materials. Fuses and circuit breakers cannot detect low level arcs, so special protection devices are sometimes used to detect them and top current flowing when arc is detected. The UL code states "By recognizing characteristics unique to arcing and functioning to de-energize the circuit when an arc-fault is detected, AFCI's further reduce the risk of fire beyond the scope of conventional fuses and circuit breakers."

Circuit breakers and fuses are protective devices that control the power going to a particular route of wiring. In case of an overload or a short on that circuit, the breaker or fuse trips and automatically shuts off power to that circuit. Fuses are the commonly used protection devices to protect components like wires, transformers electronics circuit modules against overload. The general idea of the fuse is that it "burns fuse link" when current gets higher than it's rating and thus stops the current flowing. A device called Miniature Circuit Breaker (MCB) is is used to replace fuses in electrical distribution systems (mains electrical panel). Miniature circuit Breaker can be is used in lighting distribution system or motor distribution system for protecting overload and short-circuit in the system. Miniature circuit breaker has a "switch" on it, so it cam be used for overload and short-circuit protection as well as for infrequent on-and-off switching electric equipment and lighting circuit in normal case.

For MCBs there are two characteristics that determine at what point it will trip. The first is the rated current, and the second is the class of breaker. The breaker will hold the rated current forever. The class of breaker determines how large a surge current the breaker will allow without tripping. Breakers are defined into classes by EN 60898. Type B and C breakers are likely to be suitable for general use (but an electrician will need to do the calculations to check), with B being the more sensitive type.

The breakers used in mains distribution networks need to have very high current breakage rating because the short circuit currents supplied by the mains network (distribution wiring, transformers etc.) can be very high. Most transformer fuses will 'let through' whatever the transformer and system impedance will allow. Fuses and circuit breakers (excepting some special types) take longer than 1/2 cycle to interrupt a fault, so they will see the full fault current available through the source impedance. In low distance distribution wiring going to the house this short circuit current can be easily in the range of 5-10 kA. The main fuse and breakers must be capable of stopping this current when needed.

Ground fault circuit breakers (combination of circuit breaker and RCD) offer protection against more than just overloads. The Residual Current Device(RCD) is a special electronic/electro-mechanical protection device that cuts off the fault circuit immediately on the occasion of shock hazard or earth leakage of trunk line. Earth Leakage Circuit Breaker (ELCB) is mainly prevent eletric fire and personal casualty accident caused by personal electric shock or leakage of electrified wire netting. Residual Current Circuit Breakers (RCCB) is similar to Earth Leakage Circuit Breaker (ELCB). In mains wiring earth leakage circuit breaker is used for the protection,against electrical leakage in the circuit of 50Hz or 60Hz. When somebody gets an electric shock or the residual current of the circuit exceeds the fixed value, the ELCB/RCCB can cut off the power.

RDC's are rated by the current differential required to trip them. RCD trips if the difference between line and neutral current exceeds a preset value (30mA is common, but 5 mA, 10mA, 30mA, 100mA, 300mA and 3A types are available). Trip times are usaually specified as less than 30ms, but delay types (to provide sub circuit discrimination) are available. RCDs are implemented usually in such way that phase (live) and neutral wires pass through a sensor coil. If currents are equal there is no net magnetic field in the coil. There should be 0A differential between hot and neutral if there is no leakage to ground. If live ant neutral currents are uneqal because some current is leaking to earth, a voltage is induced in the coil and that activates a circuit breaker. Simplest RCDs have just a toroidal transformer, the L and N being monitored being fed through the middle, with the secondary feeding a trip solenoid that trip the switching element. Some more complicated ones have electronics in them to process the input signal (for example very sensitve ones and ones which sense also pulsatung DC faults). Sometimes different RCD types are classified to different classes: AC, A and B. 'normal' Class AC devices are intended for use with pure sinusoidal residual currents. Class A devices should be used if the residual current includes pulsating DC components. Class B is used when the current is DC or impulse DC.

RCD with 30mA rating is typical for a single 230V circuit. RCDs with 30mA residual current sensitivity are generally used for property and person protection. RCDs with a residul sensitivity of 100mA to 300mA are recommended for property and equipment protection (particarly where numerous items of equipment are supplied through the protected circuits). Please note that RCDs cannot protect people from serious shock which could occur if they contact both live and noutral conductors at the same time (RCs protect only against live to earth faults). RCDs cannot substitute for care, commonsense and regular maintenace. RCDs are no substitute for fuses or circuitbreakers (for complete protection both a combination of RCDs and other protection devices are needed).

A ground fault circuit interrupter or GFCI, is an electronic device for protecting people from serious injury due to electric shock. GFCIs constantly monitor electricity flowing in a circuit. If the electricity flowing into the circuit differs by even a slight amount from that returning, the GFCI will quickly shut off the current flowing through that circuit. The advantage of using GFCIs is that they can detect even small variations in the amount of leakage current, even amounts too small to activate a fuse or circuit breaker. GFCIs work quickly, so they can help protect consumers from severe electric shocks and electrocution. Even if the GFCI is working properly, people can still be shocked. However, the GFCI can act quickly to prevent electrocution. All GFCIs work in the same manner to protect people against ground faults. However, unlike the receptacle GFCI, the circuit breaker type GFCI also provides overload protection for the electrical branch circuit. GFCIs are necessary even if the product has a third wire to ground it. GFCIs provide very sensitive protection to consumers against electric shock hazards. Under some conditions, a shock hazard could still exist even if a product has a grounding wire. Consumers are encouraged to use a qualified and certified electrician to install circuit breaker-type GFCIs. Individuals with strong knowledge of electrical wiring practices, who can follow the instructions accompanying the device, may be able to install receptacle-type GFCIs. The portable GFCI requires no special knowledge or equipment to install. Some equipment have GFCI type shock protectors nowadays. Appliances that have built-in shock protectors, as now required for hair dryers, may not need additional GFCI protection (but having extra protection does not cause any problems, better be safe than sorry).

Note: You cannot use most surge protectors or even some devices that have a surge circuit in them, with or downstream of, a GFCI / RCD. It will constantly "trip" if you encounter some overvoltages. There are also some devices which have pretty high gorund leakage and can cause occasional "trip" on some situations.

An AFCI (Arc Fault Circuit Interrupter) uses electronics to recognize the current and voltage characteristics of arcing faults, and interrupts the circuit when the fault occurs. This kind of special device is needed for arc protection when it is needed, because fuses and circuit breakers cannot detect low level arcs. Since cables between the electrical panel and the end appliance are subject to arc faults, protection is needed at the source of the electrical supply. AFCI protective devices are now available as part of the circuit breaker construction. AFCI is useful here you get significant number of fires caused by bad contacts and terminal connections, particularly relevant for aluminium wiring. The UL code states "By recognizing characteristics unique to arcing and functioning to de-energize the circuit when an arc-fault is detected, AFCI's further reduce the risk of fire beyond the scope of conventional fuses and circuit breakers." Effective January 1, 2002, NFPA 70, The National Electrical Code (NEC), Section 210-12, requires that all branch circuits supplying 125V, single phase, 15- and 20-ampere outlets installed in dwelling unit bedrooms be protected by an arc-fault Circuit interrupter. Installing AFCIs in your home will require a qualified electrician. The AFCIs snap into the electrical panels. And at this time, only a few electrical panel manufacturers make AFCIs. A word of caution about the overselling of AFCIs. The risk of fires caused by arcing is real and the total US loss to electrical fires is large. AFCIs can help to reduce that risk, but it will not completely solve the problems.

AFCIs should not be confused with ground-fault circuit interrupters or GFCIs. Typically AFCI circuit breakers look similar to GFCI circuit breakers. While both AFCIs and GFCIs are important safety devices, they have different functions. AFCIs are intended to address fire hazards; GFCIs address shock hazards.

The large box-like device found on the ends of some appliance cords can be either an appliance leakage circuit interrupter (ALCI), an immersion detection circuit interrupter (IDCI) or a ground fault circuit interrupter (GFCI). They work in different ways, but they are all intended to shut off the power to an appliance under an abnormal condition such as immersion of the appliance in liquid. Just because you have an appliance with one of these devices doesn't mean that it is okay to drop the appliance in water and retrieve it while it's plugged in. If you should happen to drop an electrical appliance in water, shut off power to the circuit into which the appliance is plugged, unplug the appliance, drain the water and retrieve the appliance. The rule that "electricity and water don't mix" still applies.