Failed inspection because of tap rule

[bcngtr]

240.21 Does Not Apply

240.21 Does Not Apply

Section 240.21 tap rules don?t apply to
these service-conductor taps, because
the 240.21 requirements were developed
over a number of years for a circuit with
currents flowing one way from a single
source protected by an overcurrent
device.

 

[kwired]

Tapped off of a 480v. 800 amp breaker to a disconnect. That disconnect was 250amp feeding a 200amp panel. This was a solar install, so the 200amp panel was the main. So we ran 4/0 from the main to the disconnect, then from the disconnect to the 800amp breaker. That distance was thirty feet, and was 4/0 also. Inspector said the 4/0 from the disco. to the 800amp breaker was to small because of the tap rule. He said it had to be sized 1/3 of 800amps. So the wire needs to be 250MCM. He said if it was only ten feet, it would have been fine. So why is ten feet of wire ok, but thirty feet isn't? Ten feet can handle the amps, but thirty feet can't? I don't understand the safety aspect. Is it because of less ohms in ten feet then thirty feet? Where not getting power from the 800amp breaker, where feeding it power. Can someone also explain what is a tap and what isn't. I thought you size the wire to the load not the breaker. Thank you very much for your help.

I'M a little confused. Is the 800 amp breaker the supply or is it being fed by the conductor in question?

First you described feeding from 800 amp device to a 250 amp disconnect then to a 200 main? device. The next sentence described exactly the opposite - from 200 main to 250 disconnect to 800 amp device.

If it is the supply to the 800 amp you do not have a tap so how can you break a tap rule?

A tap is a conductor with no overcurrent protection or protection that is higher than the ampacity of the conductor.

You can supply an 800 amp breaker with 14AWG if the feeder ahead of it is 15 amps. Expensive switch but not a code violation.