National Electrical Installation Standards

Standards as High as Your Own

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Monday, March 25, 2019

Question:

Thanks for providing the holy cow and yeah I knew that answers to many interesting questions. I have a question about some protective steel plates. An industrial facility has constructed a 1 foot by 1 foot trough in the concrete floor to be used to install a wire basket cable tray. The trough is installed across a walkway that is used by forklifts and personnel. The trough is covered with plate steel to provide the walking and driving surface. A groove in the trough holds the cover in place.

Power and control cables from a control cabinet to electrical equipment are installed in the tray that is installed in the trough. The power cables are using voltages up to 480 volt. The basket is bonded with an equipment ground.

Are the plate steel covers required to be bonded and secured?

Thanks, An Iowa inspector.

A

Answer:

Hey Iowa Inspector thanks for your question and the compliment. If I understand your example correctly then no. Metal material that is likely to become energized is required to be provided with an effective fault current path as stated in 250.4(A)(5). Unfortunately, the phrase "likely to become energized" is not defined in the NEC but it is described in the NEC Style manual as " the failure of insulation". If the steel plates are separated from the cables in the tray, and will not be deflected downwards by the vehicle traffic, they would not be considered likely to become energized. Bonding the steel plates to the tray can provide additional protection if they were to become energized such as by being deflected to the extent they damaged the cable insulation as sated in the Informational Note to 250.116. Not securing them could also result in an incident if they were moved causing a trip hazard or allowing a vehicle to drop into the "trough".

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