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.