National Electrical Installation Standards

Standards as High as Your Own

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Tuesday, October 16, 2018

Question:

A metal cabinet contains service conductors, their splices, and current transformers (CT), and is located upstream of an 800-amp service disconnecting means. The CT cabinet has only PVC raceways entering and exiting the enclosure, and the engineered drawings do not show any supply-side bonding jumpers in the PVC raceways.  Is it correct to assume that this metal CT enclosure must be connected to a supply-side bonding jumper?  If so, what is the correct size bonding jumper?  Should supply-side bonding jumpers have been included in the drawings?

Although NEC Table 250.102 (C)(1) provides sizes of supply-side bonding jumpers, there seems to be no specific text section that references this table for metal enclosures.  I have looked at 250.80, 250.92, and 250.102 (C).  Can you help me connect the NEC dots to size supply-side bonding jumpers to metal CT enclosures?

Curtis Lichty

A

Answer:

Hey Curtis thanks for your question, you have the correct references. All metal enclosures (the CT cabinet) containing service conductors must be bonded as stated in 250.92(A)(2). The grounded conductor can be used to accomplish the required bonding as stated in 250.92(B)(1). In that case a supply side bonding jumper is not needed. If that is not done a Supply Side Bonding Jumper can be used as that term is defined in 250.2. The size is based on 250.102(C)(1) for a single raceway or 250.102(C)(2) for parallel raceways.

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