Derating 3 phase feeders

[Dansos]

I am running a new meter base for a 240D 3PH system that is already in use. We are pulling it off it’s main breaker in the Main panel board and moving it next to it on its own meter. The meter to disconnect and stub from main board to new splice box will stay under 24” but the run from disconnect to splice box will be approx 20’. How does derating work with a high leg delta system? I am figuring all 3 phases and neutral will all be considered current carrying conductors, which will require an 20% derate. If I am correct up to this point, can I no longer use 4/0 XHHW AL for my run to the splice box? These all stem from my main question which is the handling of classifying the 4 wires (L-L-L-N) running over there.

 

[kwired]

I am running a new meter base for a 240D 3PH system that is already in use. We are pulling it off it’s main breaker in the Main panel board and moving it next to it on its own meter. The meter to disconnect and stub from main board to new splice box will stay under 24” but the run from disconnect to splice box will be approx 20’. How does derating work with a high leg delta system? I am figuring all 3 phases and neutral will all be considered current carrying conductors, which will require an 20% derate. If I am correct up to this point, can I no longer use 4/0 XHHW AL for my run to the splice box? These all stem from my main question which is the handling of classifying the 4 wires (L-L-L-N) running over there.

Unless you are using the high leg to supply 208 volt to neutral loads, (almost never is done) the neutral only is "neutral" to the 120/240 side of the delta and only carries imbalance on that side of the delta - exactly same as for 120/240 single phase supplies so not a current carrying conductor for purpose of ampacity adjustments in 310.15.

 

[Dansos]

Thanks kwired. So all that worrying for nothing hahahaha.