Feed through wire size

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AKB

Just wondering
Location
Hillsdale, NJ
Occupation
Contractor
Hi, I have a 400 A MCB 3-P main panel with feed through lugs. I used 4/0 Cu wire to 200 A fused disconnect.
Inspector says, you can't use 4/0, it has to be 500 MCM or larger.
Am I not protecting 4/0 with 200 A fuses? Any relevant code section in NEC says I need to use full size from feed through to 200 A fused disconnect?

Thank you,
 
Look at 240.21. What you have created is a tap so the tap rules apply to the #4/0 conductors.
 
If the entire run of #4/0 is outside then the inspector is incorrect. Although a tap rule would apply outsides taps can be of unlimited length.
 
AKB said:
Main panel to my fused disconnect which is fed-through main panel is about 7'.
Click to expand...
AKB said:
Am I not protecting 4/0 with 200 A fuses?
Click to expand...
With only 7' of conductor length you have a code compliant tap so the inspector is incorrect. The 200 amp fuses are not protecting the #4/0's between the panel and the 400 amp OCPD.
 
Your #4/0's are fine as tap conductors. The #4 EGC is too small because it is sized according to the OCPD ahead of the tap which is 400 amps. A 400 amp OCPD would require a #3 copper EGC.
 
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