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What is the National Electrical Safety Code?

Updated on July 8, 2020
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Tamara Wilhite is a technical writer, an industrial engineer, a mother of two, and a published sci-fi and horror author.

What is the National Electrical Safety Code?

The National Electrical Safety Code or NESC provides guidelines for engineers and technicians to safely install and maintain power stations, transformers, utility wiring and generators of all types.

The National Electrical Safety Code also covers telecommunication lines like phone lines and fiber optic cables, since these telecom lines present a shock hazard to technicians working on them. The NESC is separate from the National Electrical Code or NEC. The NESC was updated in 2017. The National Electrical Safety Code is updated every five years.

Power Transformer

NESC covers the design of power transformers like this one and the electrical substations to which they connect.
NESC covers the design of power transformers like this one and the electrical substations to which they connect. | Source

What Does NESC Include?

The NESC covers the proper design of electrical operations, though design requirements also come from the NEC. The NESC also addresses proper installation and construction techniques, an area not touched by the NEC.

NESC also covers the safe installation of telecommunication lines such as phone lines and network cables. The National Electrical Safety Code describes the approved methods of maintaining power generators, electrical substations and power switching stations.

The National Electrical Safety Code lists good practices for the installation and maintenance of the utility wiring to buildings. The NESC outlines appropriate methods to enclose generators, such as putting generators inside a room with restricted access or surrounding electrical substations with a fence.

The National Electrical Safety Code or NESC requires enclosures that limit the likelihood that unauthorized people such as passerby or untrained workers do not come into contact with powered equipment. The NESC does not use the higher standard of "prevent entry", since thieves and malicious parties may over-ride safety measures put in place, and that is not the fault of the operator who has taking reasonable security precautions.

NESC also covers allowed methods to ground electrical systems. NESC outlines the minimum distances of the fence from the sub-station, but designers are allowed to place the fence even farther away.

NESC requires that electrical supply station rooms be non-combustible as much as possible. The allowance "as much as possible" is made because oil filled transformers and generators are theoretically combustible. Combustible items are not allowed in a power substation room unless the items are spare parts required to maintain the electrical supply station. However, these items must be far enough away from the live substation to have a low risk of catching fire.

NESC requires lighting be installed at normally manned electrical substations. Outdoor lighting is not required for stations that are supposed to be unattended. Portable lighting is allowed when someone is performing maintenance at a normally unattended station. Emergency lighting that runs at least ninety minutes after a power outage is mandatory for attended substations.

NESC also sets standards for the electrical substation's layout. Floors must be even and non-slip. Floor openings must have railings. Railings are necessary if the walkway or a platform is elevated more than one foot above the floor. Stairs must have handrails if there are more than four steps. Passageways should have at least seven feet of unobstructed headroom if possible, and any obstructions that cannot be removed must be painted or marked. All exits from the substation must not be obstructed and swing outward. Double exit doors are preferred.

What NESC Does Not Cover?

The National Electrical Safety Code or NESC does not cover electrical wiring in mines, ships, railroads, aircraft or automobiles. NESC does not cover car mechanic working on a truck or an electrician on a submarine. Rules and regulations on how to run an electrical safety program are the purview of OSHA.

The NESC does not address how the utilization wiring is handled inside of the building. NESC does not cover earthquake ratings or seismic protection of equipment. IEEE standard C27.114 and IEEE 693 may be used, depending on local design codes.

The National Electrical Safety Code does not set standards for power plugs and receptacles; the design of these items is generally set by the National Electrical Manufacturers Association or NEMA. NESC requires all substations have fire extinguishers.

NFPA sets the standards for fire extinguisher design. NESC requires the signs be placed by every entrance point to the electrical equipment. NESC references ANSI standard Z535 for safety sign applications such as the size, design and wording of electrical hazard signs.

Related Standards

The National Electrical Code or NEC is published by the National Fire Protection Association or NFPA. NFPA initially published the NEC in response to the number of fires started by faulty electrical installations and poor electrical system designs.

The NEC is also called NFPA 70. The NEC has been adopted as law in many municipalities and states. The National Electrical Code is updated every three years. The NEC focuses on rules for the installation of electrical wiring in commercial, residential and institutional buildings in a way that minimizes the risk of fire.


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