Aux power take off from Inverters AC bus

[kjrise]

I'm looking at taking off a 30amp feed from a 500kw inverters 208vac bus to feed some local aux power. (this is separate from the 1400amp coming out of the inverter)
I'm running a #10 thhn to a 30amp fused switch then to a control panel.
Does NEC 240.21 (B)(1)(4) apply to this type of tap? Do i need to bump up the #10 to 1/0 because of the 1/10th rule for just a 20amp load?

 

[jaggedben]

I can't see how 240.21 (B) would not apply. The fact that PV is involved doesn't change anything about that.

Additionally, you may also have an issue with 690.14 (C). "Means shall be provided to disconnect all conductors in a building or other structure from the photovoltaic system conductors." I would advise against making a tap on the load side of the last OCPD feeding the inverter(s) (unless, perhaps, the loads being fed by the tap are integrally related to the PV system and don't need to be on when it is not.) Can't tell from your description if that's what you're considering though.

 

[jaggedben]

One thing to add...

I can't see how 240.21 (B) would not apply

...unless the 'bus' you are talking about is the service entrance conductors for a supply side connection to the inverters. But I don't imagine that's what you had in mind, I'm just covering my a--. ;-)

 

[kjrise]

The point at which we want to tap is on the same bus as where we land the wires out to the MV step up transformer.
So this will have green power flow during the day and brown power at nite from the utility. This is to give the inverter the required aux power to run the fans during the day and night time control power.