How to wire Main Breaker for Homeline subpanel

woodardhsdJanuary 24, 2011

I recently bought this subpanel (Square D, HOM612L100SCP) for my small detached workshop, see link below.

Just going to have 2 circuits initially, 1 20A for receptacles and 1 15A for lighting. In the instructions it mentions wiring using the main lugs or a main breaker, but I didn't see anything about how to actually wire the main breaker.

How do I go about doing this? Is it even worth doing with just two breakers anyways?



Here is a link that might be useful: Square D Panel

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Ron Natalie

If you have a main lug panel, there won't be any main breaker to connect to. You connect to the main lugs on the panel, takes a big hex wrench. This panel has no provision for a main breaker. It is protected by the breaker on the feeder (in your main panel). The grounded conductor (neutral) feeds the large lug feeding the terminal bar. You must remove the screw that joins the terminal bar to the case and install the separate equipment grounding bar and connect the incoming equipment ground conductor to that. I believe Schneider now provides the equipment ground bar with the panels, you used to have to buy it separately.

    Bookmark   January 24, 2011 at 10:54AM
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Did you take into consideration the existing load on your main panel board? to do something like this you really are supposed to do a load calculation on the whole house, to determine if the existing service can accommodate the additional load. How big is your service? how much service do you plan on running to the sub panel?

Also, I'll say it again, because it really is important that you separate the neutral from the ground in the subpanel, and it's also really important that you DO NOT install the bonding jumper. it's probably a little green screw that goes through the neutral bar into the case. take it out and throw it away!
Hope this helps.

    Bookmark   January 25, 2011 at 12:38PM
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My panel is a 200A (currently have 355A worth of breakers), the main breaker (not actually in the main panel box, but outside below below the meter) is a 150A.

I only plan to have 2 circuits, one 20A for receptacles, and one 15A for lighting. I'm running 10/3 (due to the distance) UF the 110' to shed. It's basically a glorified storage shed for my motorcycle and riding mower, so I don't ever see the need for any more circuits.

    Bookmark   January 28, 2011 at 1:56PM
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"currently have 355A worth of breakers"

Means absolutely nothing.

    Bookmark   January 28, 2011 at 3:58PM
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You may be able to "backfeed" a two-pole breaker at your sub-panel. That is, you ignore the two hot lugs and connect the two hot wires to the "pseudo-main" breaker (my term) so that the incoming current goes through the breaker "backwards" to the hot busses. HOWEVER, to do this legally, you'll need a hold-down kit for the backfed breaker to prevent someone from pulling out an energized breaker accidentally or ignorantly. I have no idea whether a hold-down kit is available for that particular panel.

Another possible low-cost workaround is to install a cheap disconnect ahead of the panel. 30- 60- and/or 70-amp disconnects (often marketed as air conditioning disconnects) can be purchased at big box stores for as low as about $10.

Because you're planning to put a six-slot panel in a separate building, you'll also need to drive at least one (and probably two) grounding electrode(s) to be connected to the panel ground bar with #6 (or larger) copper wire.

Since you seem pretty certain that you'll never need more than those two circuits, it might be worth pointing out that you may have another available option. That is, you could run a single 20-amp circuit to the shed and skip having a sub-panel (as well as local ground rods) altogether.

In this context, the definition of "single circuit" includes what is known as a "multiwire branch circuit" (MWBC) having two hots and a shared neutral. An MWBC can then be split into what amounts to two circuits at the shed.

So, if you size both of the circuits in the shed at 20 amps, you can use one hot for your receptacles and the other for your lights, sharing the single neutral. Of course, your lighting circuit will have to be wired with #12 wire (whereas #14 would be OK for the lights if it were a 15-amp circuit) but that would probably not add anything to the costs because, as often as not, you save money by using one wire size.

The obvious disadvantage of running an MWBC without a subpanel is that if you exceed the overcurrent limit on either your lighting or your receptacles, they'll both trip simultaneously and you'll have to walk back to the house to reset. (The breaker in your main panel must be a double breaker with the hots on opposite poles -- never two independent breakers!)

If you want to investigate this second option, be sure to run it by your local AHJ (inspector or permit-issuing office) first. Based on a couple of anecdotal accounts I've read on this forum, some local codes do not permit the MWBC approach. YMMV.

    Bookmark   January 29, 2011 at 11:47AM
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