How to Use the Tables in Art. 250 of the NEC

Electrical professionals who employ NFPA 70, National Electrical Code^® (NEC^®), on a regular basis understand the importance the NEC plays when it comes to the installation of safe electrical systems. In the beginning pages of the standard, its purpose is clearly stated as “the practical safeguarding of persons and property from hazards arising from the use of electricity.” To take it a step further, the purpose of the NEC could never be accomplished without the proper application of Art. 250 — Grounding and Bonding.

While all of Art. 250 is crucial to a safe installation, many errors evolve from incorrectly using the tables that size grounding electrode conductors (GECs), bonding jumpers, and equipment grounding conductors (EGCs). Whether you are an engineer designing the job, an electrician installing equipment, or an inspector verifying a correct installation, applying these tables is paramount to ensuring the safety of both persons and property.

To help workers understand the crucial role these tables hold in a safe electrical system, NFPA created a new fact sheetthat walks you through the proper application of the following tables within Art. 250:

Table 250.66 — Grounding Electrode Conductor for Alternating-Current Systems
Table 250.102(C)(1) — Grounding Conductor, Main Bonding Jumper, and Supply-Side Bonding Jumper for Alternating-Current Systems
Table 250.122 — Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment

In July, NFPA hosted an NEC Facebook Live event to discuss the “top 10 grounding and bonding questions” the organization gets asked about from professionals in the field. Hear the discussion and check out the comments by visiting the NEC Facebook page. Additional information about grounding and bonding is available on NFPA’s website. For more information related to the NEC, please visit nfpa.org/ElectricalSolutions.

Hannahs is an electrical content specialist with the National Fire Protection Association in Quincy, Mass. He can be reached at [email protected]. .

NOTE: This article first appeared as a post on NFPA’s blog, NFPA Today, on July 16, 2020, and has been edited.