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Wednesday, October 4, 2023

Question:

Hi CQD, my question concerns 240.4B where it talks of overcurrent devices rated 800 amperes or less. Does this rule also apply to parallel installations?

For example: Can a 400A sub-panel be supplied by paralleled two (2) sets of Aluminum-4/0 XHHW conductors, assuming terminals are 75ºC? Thanks, Alex Owen
A

Answer:

Hello Alex, great topic. Yes, Section 240.4(B) can be applied when sizing an OCPD for paralleled conductors. The ampacity for two (2) sets of Aluminum 4/0 XHHW conductors at 75ºC would be 360A per Table 310.15(B)(16). This conductor sizing would be permitted if the load demand for the new sub-panel does not exceed 360A. See Section 215.2(A)(1)(a)-(b) for more information on feeder conductor sizing.

The OCPD can be sized in accordance with Section 240.4(B). Per Table 240.6(A) 360A is not a standard size OCPD, so the next size (400A) could be used.

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