Make Your Mark: Electrical circuits and equipment markings in the NEC

By Mark C. Ode | Feb 15, 2022
NEC 2020 Cover

In the past few Code cycles, more emphasis has been provided on marking electrical branch circuits and feeders to indicate where the source of energy originates, the amount of fault current available at the service and how fast the service overcurrent device will open in a fault condition. The markings’ purpose is to provide more information involving the source’s identification so the circuits can be shut down by putting them into an electrically safe work condition or to implement lockout/tagout procedures as required in NFPA 70E Article 120, and especially with the eight different steps in 120.5 of NFPA 70E. This has been a concentrated effort to more closely align the NEC with the safety requirements found in NFPA 70E and OSHA. Here are these requirements’ locations in the NEC.

Section 110.16(B) was added in the 2017 NEC to require a permanent label to be field- or factory-applied to service equipment rated at 1,200A or more at other than dwelling units. This label must meet the requirements in 110.21(B) and contain the following information: “(1) Nominal system voltage; (2) Available fault current at the service overcurrent protective devices; (3) The clearing time of service overcurrent protective devices based on the available fault current; and (4) The date the label was applied.”

One exception to this requirement that states, “service equipment labeling shall not be required if an arc flash label is applied in accordance with industry practice.”

The purpose of this label at the service overcurrent protective device is to help determine incident energy levels, arc flash boundaries and required PPE levels based on NFPA 70E Article 130.

Section 110.16(B) sends us to 110.21(B), Field-Applied Hazard Markings. This states that where caution, warning or danger signs or labels are required by the NEC , the labels must meet the following requirements: “(1) The marking shall warn of the hazards using effective words, colors, symbols, or any combination thereof; (2) The label shall be permanently affixed to the equipment or wiring method and shall not be handwritten, unless the portions of labels or markings are variable or could be subject to changes, then handwritten is permissible but shall be legible; and (3) The label shall be of sufficient durability to withstand the environment.”

A label will be installed to encourage the electrician or maintenance person to work on it in a deenergized condition.

In addition, 110.22(A) requires each disconnecting means to be legibly marked to indicate its purpose, unless located and arranged so the purpose is evident. For the 2020 NEC , an additional sentence has been added to this section that states “in other than one- or two-family dwellings, the marking shall include the identification of the circuit source that supplies the disconnecting means.”

This label applies to all branch-circuit and feeder disconnecting means to ensure that the circuit’s source can be easily identified, disconnected and locked out/tagged out, again to ensure the electrician or maintenance person works on it in a deenergized condition.

Dealing with field labeling or marking, 110.24 requires service equipment, at other than dwelling units, to be legibly marked in the field with the available fault current. The field marking(s) shall include the date the fault-current calculation was performed and be of sufficient durability to withstand the environment involved. The calculation must be documented and made available to those authorized to design, install, inspect, maintain or operate the system. In other words, to most professionals working on the electrical system.

Modifications or changes

If there are any modifications or changes that might affect the available fault current at the service, the available fault current must be verified or recalculated as necessary to ensure the service equipment ratings are sufficient for the available fault current at the line terminals of the equipment.

The requirements that I have just covered in 110.16(B), 110.21(B), 110.22(A) and 110.24 are normally required at time of initial equipment installation and may require the action of the electrical contractor, not the electrical engineer, unless the engineer is being paid specially for these labels and applications.

Another marking requirement for disconnecting means in 450.14 states that transformers, other than Class 2 or Class 3 transformers, must have a disconnecting means located either in sight of the transformer or in a remote location. When the disconnecting means is in a remote location, it shall be lockable open in accordance with 110.25, and its location shall be field-marked on the transformer. This again ensures the transformer can be easily disconnected so the person can turn it off before working on it. Altogether, marking and identifying branch circuits and feeder disconnecting means increases safety.

About The Author

ODE is a retired lead engineering instructor at Underwriters Laboratories and is owner of Southwest Electrical Training and Consulting. Contact him at 919.949.2576 and [email protected]





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