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The NEC® 2014
Section 250.54 Auxiliary Grounding Electrodes
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Section 250.54 - Auxiliary Grounding Electrodes |
Auxiliary electrodes are permitted, but they have no requirements since they serve no useful purpose related to electrical safety addressed by the NEC. Figure 250–121
Figure 250-121
If an auxiliary electrode is installed, it’s not required to be bonded to the building grounding electrode system, required to have the grounding conductor sized to 250.66, or comply with the 25-ohm requirement of 250.53(A)(2) Ex. Figure 250–122
Figure 250-122
CAUTION: An auxiliary electrode typically serves no useful purpose, and in some cases it may actually cause equipment failures by providing a path for lightning to travel through electronic equipment. Figure 250–123
Figure 250-123
DANGER: Because the contact resistance of an electrode to the earth is so great, very little fault current returns to the power supply if the earth is the only fault current return path. Result—the circuit overcurrent device won’t open and clear the ground fault, and all metal parts associated with the electrical installation, metal piping, and structural building steel will become and remain energized.
This Article is extracted from Mike Holt’s Understanding NEC® Requirements for Grounding vs. Bonding, based on the 2014 NEC®. To order your copy of the full program, click on the image below or visit www.MikeHolt.com/14grounding and save 20% when you use discount code NL14GvB.
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