Article and photos by Gregory Havel
Since electric service to buildings has been provided for more than 100 years, materials and methods have been developed to make them safe installations for regular use. However, there is still some hazard from these services outside the building, especially if you are working near an overhead service or digging near an underground service.
A specific potential hazard to firefighters is disconnecting the electric service at a fire incident at a building. The safe and proper way to accomplish this is to shut off and lock out the main disconnect switch or circuit breaker, if it is accessible. If it is not accessible, call the utility company to disconnect the service to the building.
Especially hazardous to firefighters is a procedure that was still being taught a few decades ago and that is still part of the operational procedure of some fire departments. This involves removing the electric meter from its socket on the outside of the building without wearing the proper personal protective equipment (PPE).
Photo 1 shows the underground electrical service that is typical at residences and small commercial buildings. The utility company wires feed into the meter from the bottom through the vertical duct. The electrical contractor connects the interior building wiring to the proper terminals. When the utility company installs the meter, the connection is complete. Meter enclosures are sealed or locked to prevent theft of electricity and to prevent opening by unauthorized persons. Smaller-sized electric services like this one use a simple meter socket in which the electric meter completes the circuit–as does the service in photo 2.
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Photo 2 shows the inside of a simple meter socket for an overhead electric service. (The interior of the meter socket in photo 1 is similar.) The utility company wires are connected to the top terminals, and the neutral (white) wire to the center terminal. When the utility meter is installed, its contacts (arrows) complete the circuit between the utility company wires and the house wires up to the main disconnect switch or circuit breaker inside the building. This type of meter socket has electricity at high voltage, usually 240 or 208 volts between the two black wires and 120 volts between either of the black wires and the neutral (white) wire or to ground.
This type of meter is sometimes called a “feed-through” meter because the electrical current used feeds directly through the electric meter. Although removing this meter will disconnect electrical current from the house, it will leave exposed energized contacts in the meter socket. In addition, there is a great risk of an “arc flash” and the risk of burns, other injuries, and electrocution for anyone nearby.
An arc flash can be defined as the release of energy as light, heat, and sound during an electrical arc. This condition can cause personal injury (temporary or permanent blindness, severe burns, temporary or permanent hearing loss) or fatality and can also ignite fires.
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Photo 3 shows the inside of a metering cabinet for a larger commercial electrical service. This type of metering cabinet has voltage that is much more hazardous than a residential service. The three-phase service shown in photo 3 has the building wiring in place between the meter cabinet and the main disconnect switch inside the building. It will operate at 480 volts between any pair of brown, orange, or yellow wires and at 277 volts between the gray (neutral) wire and any one of the brown, orange, or yellow wires, or to ground. This service can provide such large amounts of electrical energy that a “feed-through” meter is impractical. Instead, devices called “current transformers” are installed between the pairs of terminals labeled “AA,” “BB,” and “CC.” These transformers create a smaller induced electrical current from each phase conductor and transfer it by smaller wires to the meter socket on the outside of the cabinet door through the connection at “M”. The utility company will connect its conductors to the terminals labeled “U” on the opposite side of the current transformers from the building wiring.
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Photo 4 shows the outside of the electrical metering cabinet and the meter socket. The electric meter is similar to the one shown in photo 1, except that it meters electrical current on three conductors instead of two and meters indirectly by way of the current transformers.
Removing this type of meter will not disconnect the electricity to the building and will leave energized meter contacts exposed. In addition, there is a great risk of an “arc flash” and of burns, other injuries, and electrocution for anyone nearby.
According to National Fire Protection Association (NFPA) Standard 70E Electrical Safety in the Workplace, 2009 edition, work on energized electrical equipment, including meters and metering cabinets, must be done by a “qualified person.” A qualified person is “One who has skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training to recognize and avoid the hazards involved.” (NFPA 70E Article 100) A qualified person for meter removal would be an electrical utility employee. The hazards involved include the arc flash hazard, defined as the release of energy as light, heat, and sound during an electrical arc, and the hazard resulting from removed electrical meters.
Part of the training of a qualified person is the use of arc-flash-rated PPE. For removal of energized electrical meters up to 600 volts at residential and commercial buildings, the qualified person’s PPE listed in NFPA 70E includes the following:
· Fire-retardant arc-rated long-sleeve shirt and trousers (or coveralls)
· Non-conductive hard hat ANSI-rated G and E
· Safety glasses or safety goggles
· Arc-rated face shield or arc-flash suit hood
· Arc-rated jacket
· Rubber insulating gloves rated for the system voltage, with leather protectors
· Hearing protection (ear canal inserts)
· Leather work shoes (non-conductive preferred)
Although PPE for interior structural firefighting may provide limited protection against arc flash, it should not be used for this purpose, since it has not been tested or rated for arc flash exposure. In addition, arc-flash-rated PPE is assumed to be dry. Most firefighters’ PPE at an incident will not be dry and, as a result, will be electrically conductive.
Rather than remove the electric meter from a fully involved structure, the utility company is likely to disconnect the service to the building at the transformer on the pole or on the ground nearby and to remove the meter at a later time when it is safe to do so. In most parts of North America, utility workers are not permitted to reconnect an electrical service or to replace an electrical meter until a qualified electrician has repaired the electrical system and the building department or electrical inspector has inspected and approved the repairs.
Since most fire investigators are not “qualified persons” as defined by NFPA 70E, for their own safety they must ensure that the utility company has disconnected the electric service to the building before they begin to open covers on electrical boxes, switchgear, or other electrical equipment.
If the service has not been disconnected, for their own safety fire investigators must follow the lockout procedures outlined in NFPA 70E Article 120 [especially Article 120.2 (D) (2)] before opening covers on electrical boxes, switchgear, or other equipment. In this instance, a qualified electrician, with the proper training and PPE, should work with the investigation team to assist in managing the risks of energized electrical parts arc flash.
Gregory Havel is a member of the Burlington (WI) Fire Department; a retired deputy chief and training officer; and a 30-year veteran of the fire service. He is a Wisconsin-certified fire instructor II and fire officer II, an adjunct instructor in fire service programs at Gateway Technical College, and safety director for Scherrer Construction Co., Inc. Havel has a bachelor’s degree from St. Norbert College; has more than 30 years of experience in facilities management and building construction; and has presented classes at FDIC.
Subjects: Building construction for firefighters
