National Electrical Installation Standards

Standards as High as Your Own

Thursday, February 28, 2019


Re: CQD answer published Thursday, February 21, 2019 -

Re Wed Feb 20 CQD about phase conductors separated into different conduits. Your answer is perfect - and I am only accenting the excellent but easily missed concept of 300.20(B). We did this for a 3-foot long, 1600 amp, 3-Phase run between a buss-duct terminal and the machine's input box. Matching lengths of these very short conductors would have been very difficult had we not run them as lug-aligned A - B - C conduits. We used non-metallic (PVC) conduits as is necessary, BUT you must also remember to comply with 300.20(B) by cutting slots between the conduit holes if the enclosure is metallic .  Otherwise that sheet of metal becomes an induction heater. Of course, full circuit-sized EGC conductors are required in each conduit.

Scott Cline



Hey Scott thanks for your comments and confirming our answer. The example you shared is a good one where installing the "phase conductors" in separate raceways could be necessary to facilitate making the terminations. Cutting slots between the raceway entries in metal enclosures is a common method of preventing heating caused by induced currents.

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