112kVA Transformer to Two 200A Panels

7 replies [Last post]
Pipeandwire's picture
Joined: 2016-10-07

Hey guys,

I'm looking to clarify an install with a 112kVA transformer, 480V primary, 208Y secondary. The transformer is going to be next to dp and secondaries are going to be located next to the transformer so the within 10 ft distance rule will apply.

My question is should I put a 400A fused disconnect and feed the two panels from there and go mlo at the panels or put a 200A main in each of the panels? The third option I guess would be feeding one panel and double lugging and feed 2nd panel from there.

Looking forward to any suggestions. Thanks

sparky377's picture
Joined: 2013-10-07

All three of your suggestions are acceptable design options.

But I have to ask. Is there a reason for two separate panelboards with the same voltage and bus rating? If not, then I would suggest using one 400A main circuit-breaker panelboard. Whether the panelboard is two sections with through-feed lugs from the first section to the second section, or one cabinet, it will still be one panelboard. You may be able to save material and labor cost by installing a single, larger cabinet rather then two cabinets and have to interconnect them. After all, you are now permitted to install up to 84 poles in a single enclosure.

allyson1's picture
Joined: 2017-01-17

I share the same opinion with Wed, it is preferable to use a single circuit-breaker panelboard 400 A.
It is really economical.

Sparky43207's picture
Joined: 2015-04-03

The problem with a fused switch and MLO panels is that the panels would also have to be rated for 400A. I will agree with the other two that a single panel would be the best option.

T Dittmar's picture
Joined: 2016-05-06

A single 400A MCB panel is the most economical solution.

Garryout's picture
Joined: 2016-11-14

If you absolutely have to have two separate panelboards (i.e., for convenient submetering of two tenants), you could feed two 200A MCB panels with separate feeders as long as each feeder complies with the 10 ft tap rule. See note 2 under NEC Table 450.3(A).

mshields's picture
Joined: 2014-10-08

Just be sure to use fully rated conductors on your secondary, whichever way you go. The "next size up" rule does not apply.

mshields's picture
Joined: 2014-10-08

Two panels are fine if that's what you need, for whatever reason. Just be sure to use fully-rated cable for the secondary OCPD(s) since the "next size up" rule does not apply to transformer secondaries.

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