Thoughts....

infinity said:
In post #28 Augie has given you the other option.

The way it's depicted in the Detail A you have the XFMR>400 amp Disconnect>Wireway>Tap Conductors to line side of 100 amp circuit breakers. After that you have 4 feeders to each individual temp panel. Those feeder are currently designated as #2 Aluminum. Since #2 Al is only rated for 90 amps and 90 amps is a standard size they cannot be used for 100 amps.

1770739445218-png.2581926
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What problems could arise from using #2 instead of #1?
 
Alwayslearningelec said:
Well they are sizing the MC cable to the 90 degree column. What problems could arise from this? E.g. we need 400A but they are running (2) sets of 4/0 AL MC cable.
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Parallel sets of #4/0 are only good for 360 amps (2*180 amps) so you cannot use that for the transformer secondary conductors to the 400 amp disconnect unless there is an OCPD of 350 amps or less in the disconnect.

Alwayslearningelec said:
What problems could arise from using #2 instead of #1?
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Most likely nothing other than it being a code violation.
 
infinity said:
Parallel sets of #4/0 are only good for 360 amps (2*180 amps) so you cannot use that for the transformer secondary conductors to the 400 amp disconnect unless there is an OCPD of 350 amps or less in the disconnect.


Most likely nothing other than it being a code violation.
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Is there a reason why 240.4(B) wouldn't apply here?
 
JoeStillman said:
Is there a reason why 240.4(B) wouldn't apply here?
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The next size up rule cannot be used for transformer secondary conductors due to 240.21(C).

240.21(C) Transformer Secondary Conductors.
A set of conductors feeding a single load, or each set of conductors feeding separate loads, shall be permitted to be connected to a transformer secondary, without overcurrent protection at the secondary, as specified in 240.21(C)(1) through (C)(6). Section 240.4(B) shall not be permitted for transformer secondary conductors.
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