National Electrical Installation Standards

Standards as High as Your Own

Thursday, August 9, 2018


Is acceptable a TEMPORARY 120lnft AC feeder (4-2/0 & 1-#4 gnd) running through plenum area without conduit? Also, a 150lnftDC 2/0 feeder running in the same way?

Rafael Colon



Hey Rafael thanks for your question. You don't say what the temporary wiring is for or which type of wiring method is used for the feeders. Rules in Chapters 7 through 7 can modify the rules in Chapters 1 through 7 as stated in the second sentence of 90.3. Certain cable assemblies and flexible cords can be used for feeders installed as temporary wiring under the conditions provided as stated in 590.4(B). For example, NM cable can be used for temporary wiring in any building or structure because this section modifies 334.10 and 334.12. Typically, this is done during the time periods described in 590.3(A) when the area is not being used for its final intended purpose. The rules in 300.22(C) which apply to spaces used for air handling (plenums) are not specifically modified in Article 590 so they still apply as stated in 590.2(A). If the space is being used as an air handling space, during the time the temporary wiring is installed, it seems the wiring needs to meet the rules in 300.22(C). The AHJ will need to make the final determination.

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