Inadequate or improper electrical wiring was one of OSHA's top 10 most commonly cited violations during 2016. An electrical wiring hazard exists when:
Normally, the circuit breaker in a circuit is matched to the wire size. However, in older wiring, branch lines to permanent ceiling light fixtures could be wired with a smaller gauge than the supply cable. Let's say a light fixture is replaced with another device that uses more current. The current capacity (ampacity) of the branch wire could be exceeded. When a wire is too small for the current it is supposed to carry, the wire will heat up and could cause a fire.
When you use an extension cord, the size of the wire you are placing into the circuit may be too small for the equipment. The circuit breaker could be the right size for the circuit but not right for the smaller-gauge extension cord. A tool plugged into the extension cord may use more current than the cord can handle without tripping the circuit breaker. The wire will overheat and could cause a fire.
The kind of metal used as a conductor can cause an electrical hazard. Special care needs to be taken with aluminum wire. Since it is more brittle than copper, aluminum wire can crack and break more easily. Connections with aluminum wire can become loose and oxidize if not made properly, creating heat or arcing.
You must recognize that inadequate wiring is a hazard.
Electrical hazards exist when wires or other live electrical parts are exposed.
You must recognize that an exposed electrical component is a hazard.
Five workers were constructing a chain-link fence in front of a house, directly below a 7,200-volt energized power line. As they prepared to install 21-foot sections of metal top rail on the fence, one of the workers picked up a section of rail and held it up vertically. The rail contacted the 7,200-volt line, and the worker was electrocuted. Following inspection, OSHA determined that the employee who was killed never received any safety training from his employer and no specific instruction on how to avoid the hazards associated with overhead power lines. In this case, the company failed to obey these regulations:
The risk from exposed live parts depends on your distance from the parts. Three "boundaries" are key to protecting yourself from electric shock and one to protect you from arc flashes or blasts. These boundaries are set by the National Fire Protection Association (NFPA 70E-2015).
Overloads in an electrical system are hazardous because they can produce heat or arcing. Wires and other components in an electrical system or circuit have a maximum amount of current they can carry safely. If too many devices are plugged into a circuit, the electrical current will heat the wires to a very high temperature. If a tool uses too much current, the wires will heat up.
The temperature of the wires can be high enough to cause a fire. If their insulation melts, arcing may occur. Arcing can cause a fire in the area where the overload exists, even inside a wall.
To prevent too much current in a circuit, a circuit breaker or fuse is placed in the circuit. If there is too much current in the circuit, the breaker "trips" and opens like a switch. If an overloaded circuit is equipped with a fuse, an internal part of the fuse melts, opening the circuit. Both breakers and fuses do the same thing: open the circuit to shut off the electrical current.
If the breakers or fuses are too big for the wires they are supposed to protect, an overload in the circuit will not be detected and the current will not be shut off. Overloading leads to overheating of circuit components (including wires) and may cause a fire.
You must recognize a circuit with improper overcurrent protection devices - or one with no overcurrent protection devices at all - is a hazard.
Overcurrent protection devices are built into the wiring of some electric motors, tools, and electronic devices. For example, if a tool draws too much current or if it overheats, the current will be shut off from within the device itself. Damaged tools can overheat and cause a fire.
You must recognize that a damaged tool is a hazard.
Insulation that is defective or inadequate is an electrical hazard. Usually, a plastic or rubber covering insulates wires. Insulation prevents conductors from coming in contact with each other and with people.
Extension cords: Extension cords may have damaged insulation. Sometimes the insulation inside an electrical tool or appliance is damaged. When insulation is damaged, exposed metal parts may become energized if a live wire inside touches them.
Tools: Electric hand tools that are old, damaged, or misused may have damaged insulation inside. If you touch damaged power tools or other equipment, you will receive a shock. You are more likely to receive a shock if the tool is not grounded or double-insulated. Double-insulated tools have two insulation barriers and no exposed metal parts.
You must recognize that defective insulation is a hazard.
When an electrical system is not grounded properly, a hazard exists because unwanted voltage cannot be safely eliminated. The most common OSHA electrical violation is improper grounding of equipment and circuitry. The metal parts of an electrical wiring system that we touch (switch plates, ceiling light fixtures, conduit, etc.) should be grounded and at 0 volts. If the system is not grounded properly, these parts may become energized. Metal parts of motors, appliances, or electronics that are plugged into improperly grounded circuits may be energized. If there is no safe path to ground for fault currents, exposed metal parts in damaged appliances can become energized.
Extension cords may not provide a continuous path to ground because of a broken ground wire or plug. If you contact a defective electrical device that is not grounded (or grounded improperly), you will be shocked.
You must recognize an improperly grounded electrical system is a hazard.
A ground fault circuit interrupter, or GFCI, is an inexpensive life-saver. GFCIs detect any difference in current between the two circuit wires (the black wires and white wires). This difference in current could happen when electrical equipment is not working correctly, causing leakage current. If leakage current (a ground fault) is detected in a GFCI-protected circuit, the GFCI switches off the current in the circuit, protecting you from a dangerous shock.
More important points to remember:
Circuits with missing, damaged, or improperly wired GFCIs may allow you to be shocked.
You need to recognize that a circuit improperly protected by a GFCI is a hazard.
Most people do not realize that overhead powerlines are usually not insulated. More than half of all electrocutions are caused by direct worker contact with energized powerlines. Powerline workers must be especially aware of the dangers of overhead lines.
In the past, 80% of all lineman deaths were caused by contacting a live wire with a bare hand. Due to such incidents, all linemen now wear special rubber gloves that protect them up to 34,500 volts. Today, most electrocutions involving overhead powerlines are caused by failure to maintain proper work distances.
Shocks and electrocutions occur where physical barriers are not in place to prevent contact with the wires. When dump trucks, cranes, work platforms, or other conductive materials (such as pipes and ladders) contact overhead wires, the equipment operator or other workers can be killed.
If you do not maintain required clearance distances from powerlines, you can be shocked and killed. (The minimum distance for voltages up to 50kV is 10 feet. For voltages over 50kV, the minimum distance is 10 feet plus 4 inches for every 10 kV over 50kV.) Never store materials and equipment under or near over-head powerlines. We'll talk more about this topic in the next section.
Depending on the voltage of the line, a worker or a conductive object, must keep the minimum distance specified below between them and any energized part of the power line.
For more information on minimum approach distances and evaluating work zones, see Oregon OSHA's Fact Sheet on Power Line Safety.
See 29 CFR 1910.269 Tables R-3 through R-9 for more information on calculating approach distances.
There are a number of general situations and conditions in the workplace that indicate electrical hazards:
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This is an excellent electrical presentation by Rodney Sherman given at Holy Cross Energy. It will make a believer out of you.