National Electrical Installation Standards

Standards as High as Your Own

The National Electrical Code is the bedrock of the electrical construction business.

Do you know all the ins and outs of the Code? NECA and Electrical Contractor magazine are pleased to present their daily online feature, “Code Question of the Day.”

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    Wednesday, October 17, 2018


    Charlie, Thank you for your service...enjoyable and very informative. Section 300.3(B) discusses conductors of the same circuit and in general, requires that all conductors (including the grounded conductor and all equipment grounding conductors and bonding conductors) to be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4). An exception under 300.3(B)(1) - Parallel Installations - allows conductors that are installed in underground, non-metallic raceways to be arranged as isolated phase installations as long as the raceways are installed in close proximity and comply with 300.20(B). Section 300.5(I) discusses conductors of the same circuit in underground installations. This section also requires all conductors of the same circuit (including the grounded conductor and all equipment grounding conductors) to be installed in the same raceway or cable "or shall be in close proximity in the same trench." Exception No. 2 under this section, however, allows isolated phase, polarity, grounded conductor, and equipment grounding and bonding conductor installations in non-metallic raceways in close proximity where conductors are paralleled as permitted in 310.10(H), and where the conditions of 300.20(B) are met.

    Now to my question: For an underground 3 phase, 5 wire installation (3 phase conductors, an equipment grounding conductor, and a grounded conductor), can the 3 phase wires and the equipment grounding conductor be installed together in a single underground PVC conduit and the grounded conductor be installed in a separate, adjacent underground PVC conduit? The conductors are "installed in close proximity in the same trench" per the last sentence of Section 300.5(I) and this also appears to meet the general intent covered by Exception No. 2 under Section 300.5(I). However, this is not a parallel installation and each phase is not isolated. All phase conductors (and the equipment grounding conductor) are grouped together in one underground PVC conduit and the grounded conductor (the neutral) is installed in a separate underground PVC conduit with both conduits being side by side (i.e. in close proximity in the same trench). Thanks, Chris DeWeese

  • ?
    Tuesday, October 16, 2018


    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



    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.

ABOUT CQD: NECA’s Code Question of the Day (CQD) is a leading National Electrical Code® forum for NECA and the industry. The CQD generates a lively dialogue and relative practical and Code-based responses to an ever-increasing and interactive audience.

IMPORTANT NOTICE: All answers are based on the latest edition of the National Electrical Code®, unless the question requests a response based on a specific edition. This correspondence is not a formal interpretation of the NEC®. Any responses expressed to the questions are opinions and do not necessarily represent the official position of NECA, NFPA, or any technical committee. In addition, this correspondence is neither intended, nor should it be relied upon, to provide professional consultation or services.

ABOUT CHARLIE: Charles M. Trout, better known as Charlie, was a nationally known NEC® expert and author. He served on several NEC® technical committees and is past chairman of CMP-12. In 2006 Charlie was awarded the prestigious Coggeshall Award for outstanding contributions to the electrical contracting industry, codes and standards development, and technical training. Charlie was also a member of NECA’s Academy of Electrical Contracting. Charlie’s experienced team of industry experts keep the CQD dialogue and discussions active and informative in the spirit of the man himself, as he wanted.

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