Neutral Sizing

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CBL65

Member
I searched and I don't think I'm ok.

200kVA 600 to 208Y/120 Transformer.

600A Panel w/ 400A main breaker on the low side. My electricians ran 500MCM between the transformer and the panel, but since the pull was hard, they ran a 4/0 neutral.

Should I have them redo it? Loads are trailers fed from 70A fusible disconnects.
 

CBL65

Member
Office trailers. Four trailers w/ 100A panels.

600V 208Y/120
A 40.4 A 65.4 A
B 16.2 A ???
C 37.4 A 74.9 A
N XXX 17.7 A

Startup values are above. The light B phase loading is expected since there are 4 loads and three phase service.

The neutral current is pretty good for an unbalanced system (I think).

The only loads here are the HVAC and lights. We couldn't get on to the B phase in the panel due to the size of the conductors between transformer and panel. I'll probably power the system down tomorrow and pop the cover on the transformer. Then we'll put the meter on and power it back up to be read from a safe distance.

I don't think I'm going to have too much of a problem since I over-engineered all the components to future proof it.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
The neutral isn't your only potential problem. The 500 Kcmil conductors are too small. Since they are only rated for 380 amps they cannot be protected by a 400 OCPD on the secondary side of a transformer.
 

bphgravity

Senior Member
Location
Florida
The 90 degree column can generally only be used for derating purposes. The termination devices for your installation are likely only rated to 75 degrees. See 110.14(C) of the NEC.
 
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