Subpanel required for detached structure?

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buzzbar

buzzbar

Senior Member
Location
Olympia, WA
Occupation
Electrical Contractor
I'm bidding on a commercial job that has a new detached "shed" with some equipment in it. The plans call for three (3) separate 120V circuits brought from the main panel in the main building. I always thought that a detached structure needed a subpanel if there is more than one circuit, but I, for the life of me, cannot find this in the code book.

Can anyone shed (no pun intended) some light on this?

Thanks!

-Andy
 
If you have a 208 / 120 Volt 3 phase supply, then a multiwire branch circuit will give you the three 120 V circuits. Read the definition of Branch Circuit, Multiwire in Article 100.
 
You may have 3 circuits by pulling in a multi-wire branch circuit, but, to say this would be 3 separate circuits would be a stretch considering what you'd have to do to utilize the MBC.

JAP>
 
225.30 Number of Supplies. A building or other structure
that is served by a branch circuit or feeder on the load side
of a service disconnecting means shall be supplied by only
one feeder or branch circuit unless permitted in 225.30(A)
through (E). For the purpose of this section, a multiwire
branch circuit shall be considered a single circuit.
Where a branch circuit or feeder originates in these additional
buildings or other structures, only one feeder or
branch circuit shall be permitted to supply power back to
the original building or structure, unless permitted in
225.30(A) through (E).
 
jap said:
. . . 3 separate circuits . . .
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And this is "defined" by . . . what?

More importantly, we don't know anything about the loads to be served in the detached building, in the OP.
 
al hildenbrand said:
And this is "defined" by . . . what?
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Defined by the fact that these 3 circuits would have to originate from either a 3p common trip breaker or 3 1p breakers with the handles tied together with handle ties, where anyone who has done this long enough knows that it's very seldom that if the center breaker where to trip that it wouldn't take one or the other by it's side along with it.

The only way to have 3 truly separate circuits would be if the handles weren't tied together at all, which you cannot do with a MWBC.

JAP>
 
If you and I and Buzzbar were standing next to a railroad track and the train came by and wiped me out, you'd stand a lot better chance of not being affected by the incident if the 3 of us weren't holding hands when the whistle blew to begin with.


JAP>
 
jap said:
The only way to have 3 truly separate circuits would be if the handles weren't tied together at all, which you cannot do with a MWBC.
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OK. "Truly separate" might mean that, it might not . . . but there is no NEC language, all by itself, that prevents a MWBC from providing three 120 V circuits to a detached building.
 
There will be (3) separate 120V circuits. One 1P30 and two 1P20. No multiwire circuits. I’m trying to tell them that we need a subpanel, just needed the code reference, which has been noted. Thanks guys!
 
al hildenbrand said:
OK. "Truly separate" might mean that, it might not . . . but there is no NEC language, all by itself, that prevents a MWBC from providing three 120 V circuits to a detached building.
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I'm not saying there is.

My biggest gripe and the thing that makes the most sense about the whole MWBC thing is having to tie the handles together.

JAP>
 
buzzbar said:
There will be (3) separate 120V circuits. One 1P30 and two 1P20. No multiwire circuits. I’m trying to tell them that we need a subpanel, just needed the code reference, which has been noted. Thanks guys!
Click to expand...

And you would be correct.

JAP>
 
buzzbar said:
I'm bidding on a commercial job that has a new detached "shed" with some equipment in it. The plans call for three (3) separate 120V circuits brought from the main panel in the main building. I always thought that a detached structure needed a subpanel if there is more than one circuit, but I, for the life of me, cannot find this in the code book.

Can anyone shed (no pun intended) some light on this?

Thanks!

-Andy
Click to expand...

Do the plans specify the circuit numbers? A MWBC could provide the 3, tho as mentioned you need handle ties or a 3p breaker. If one circuit comes from a lighting panel and two receptacles come from another, then no, not legal.

You may want to look at the job spec to see if there's anything preventing MWBC... if so, you'll need a feeder to a subpanel anyway.
 
Or do what all your competitors are going to do and bid it exactly as it's shown on the plans and then charge them a change order to install it as it should be once they get the project since it won't pass inspection.

I see lately where the architects and engineers are making more and more mistakes on the drawings than the electrical estimator can include in his bid to do it right and still win the project on bid day.

Everyone needs to do their job starting from the top down.

JAP>
 
jap said:
Or do what all your competitors are going to do and bid it exactly as it's shown on the plans and then charge them a change order to install it as it should be once they get the project since it won't pass inspection.

I see lately where the architects and engineers are making more and more mistakes on the drawings than the electrical estimator can include in his bid to do it right and still win the project on bid day.

Everyone needs to do their job starting from the top down.

JAP>
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I couldn’t agree more. And yes, that’s what I was thinking of doing. However, this is a private job, and will not necessarily go to the low bidder. I would hope that they would want to work with somebody that gave them a head’s up prior to the start. Also, I’m not hungry for work right now, so.......
 
Sounds like we run a lot along the same path.

Good luck with it.

JAP>
 
buzzbar said:
I'm bidding on a commercial job that has a new detached "shed" with some equipment in it. The plans call for three (3) separate 120V circuits brought from the main panel in the main building. I always thought that a detached structure needed a subpanel if there is more than one circuit, but I, for the life of me, cannot find this in the code book.

Can anyone shed (no pun intended) some light on this?

Thanks!

-Andy
Click to expand...

Let's start with 1Ø or 3Ø?
 
buzzbar said:
There will be (3) separate 120V circuits. One 1P30 and two 1P20. No multiwire circuits. I’m trying to tell them that we need a subpanel, just needed the code reference, which has been noted. Thanks guys!
Click to expand...

In that case you will need a feeder panel with the appropriate grounding.
 
tom baker said:
In that case you will need a feeder panel with the appropriate grounding.
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Yeah, that's what I've always done, and dkidd shared the code reference, which is found at 225.30. The drawings provided on the bid documents show three separate circuits going back to the main panel. It goes to show that just because you can draw up plans, it doesn't mean that they're correct. I've been in the business for over 30 years, and the older I get, the more I trust my own instincts, rather than blindly follow other ideas. But I suppose that happens with age and experience. :)
 
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