112KVA 480D ~ 208Y120 transformer feeding two panels

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dxco

Member
Wasn't sure if I should post in NEC or engineering calc...
I am proposing to feed two panels from one 112KVA transformer - 480 Delta to 280/120v Wye
My plan is this:
480V protected with 175A breaker ~ 2/0 with 6AWG ground >
to primary side of transformer >
Secondary transformer to two 175A Main Breaker panels, each located less than 10ft from transformer (<10ft run) -
Secondary is 3P 4W 2/0 with 6AWG ground to each panel.

Is this scheme NEC compliant or do I need to add a panel between the transformer and the two 175A panels?


Thanks in advance - I appreciate any guidance I can get!
DX
 
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weressl

weressl

Esteemed Member
Location
Texas by the Gulf, geat crab, great shrimp
dxco said:
Wasn't sure if I should post in NEC or engineering calc...
I am proposing to feed two panels from one 112KVA transformer - 480 Delta to 280/120v Wye
My plan is this:
480V protected with 175A breaker ~ 2/0 with 6AWG ground >
to primary side of transformer >
Secondary transformer to two 175A Main Breaker panels, each located less than 10ft from transformer (<10ft run) -
Secondary is 3P 4W 2/0 with 6AWG ground to each panel.

Is this scheme NEC compliant or do I need to add a panel between the transformer and the two 175A panels?


Thanks in advance - I appreciate any guidance I can get!
DX
Click to expand...

Didn't check the sizes, but othervise you're good to go.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
infinity said:
Just curious how would you size the GEC and the system bonding jumper?
Click to expand...
Both sized per 250.66. The GEC is sized based on total cmil of secondary conductors, but the SBJ size depends on whether installed at the source or at panels, same as GEC connection at panels using taps off of main GEC.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Ragin Cajun said:
312A * 1.25 = 390A, next std OCD is 400A.
Click to expand...

I understand I can protect it at 400.

What I am missing is the advantage in doing so. I still cannot load the transformer beyond 312 amps.

The two 175 amp breakers combined are capable of 280 amps continuous or 350 non continuous.

So I guess there would be a slight advantage if you had a continuous load over 280 amps but less than 312 amps and you wanted to run the transformer at close to 100% of it's rating.
 
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nicholaaaas

Member
Location
Baltimore
I'm installing this setup right now. I ordered #6 equipment grounds. While I was putting them in a thought hit me that the grounds need to be good for the full load even though they feed separate panels. Mine are fed from a commoun trough

Sent from my SM-T217S using Tapatalk
 
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