Following my previous question about feeding a sub-panel...

I have access to a new-in-box 125A load center, which is more current than I need, but the form factor is good. Can I drop to a 60A feeder wire and breaker setup without running into any obscure code-related incompatibilities? What additional hardware do I need to install the main breaker since this one is "Main Lugs Only"?

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    Did this fall off a truck? Or do you have the opportunity for return it and shop for other choices? Since this is an outbuilding, you do need a main breaker- well, shutoff, but you may be able to get more spaces in other panel designs, e.g. the type where the main breaker sits in spaces 1-3. What's more, as usual with Homeline, they "forgot" ground buses. So you can do better in both grounb buses included and spaces-per-formfactor. – Harper - Reinstate Monica Aug 19 '18 at 18:36
  • It was acquired second-hand from a project not completed. I may be able to return it for store credit. Don't need many spaces. Just a utility shed. – isherwood Aug 19 '18 at 18:37
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    Certain colored Borg stores are astonishingly accommodating at taking back products for which you do not have a receipt or credit card. I've even accidentally returned purchases at one to the other. – Harper - Reinstate Monica Aug 19 '18 at 18:58

Yes you can get a 60A main breaker for this panel

Your panel uses what is known as a QOM1 main breaker frame size -- this is standard for Square-D panels up to 125A. While an ordinary Homeline 60A breaker won't fit there, the good news is that Square-D does make a QOM60VH -- so simply install that into your panel as per the supplied instructions, and you'll be golden as far as your main breaker goes. (Some other panel makes would require you to use Harper's approach of using a backfed branch breaker for the main, instead.)

You'll also need a PK15GTAL ground bar or two, as this will be a subpanel instead of a main panel.

  • Since I am not up on the technical terms being used (and have limited experience), I ask does this mean that the two lugs at the bottoms are removed and the QOM60VH bolted in their places. This breaker apparently has lugs on one side and bolt on connectors on the other. Also I thought one of the two neutral or ground bars could be used for neutrals and one for grounds by disconnecting some strap or removing some green screw? Why does one of the bars have a large lug on it and the other doesn't? – Jim Stewart Aug 19 '18 at 21:08
  • @JimStewart -- you are correct that the main lugs get removed and the main breaker gets bolted down in their place. As to the neutral bars -- the Square-D interior design has a screw that's fitted/pulled to bond/unbond the neutral to/from the enclosure, but for subpanel use, a separate ground bar is required. The large lug is for the incoming neutral wire. – ThreePhaseEel Aug 19 '18 at 21:12
  • Why can't one remove the large strap on the bottom, use the right hand bar as the neutral and insert a screw that bonds the left hand bar to the case and maybe get a lug which will accept the large ground from the main panel? Why are there so many small lugs for neutrals and grounds? – Jim Stewart Aug 19 '18 at 21:22
  • @JimStewart -- the need for the small screws is to provide enough places to land N and G wires when this is used as a service entrance panel -- the large strap on the top of the interior (the photo has it upside down) does not come off on this design, I believe. – ThreePhaseEel Aug 19 '18 at 21:57
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    @JimStewart -- the PK15GTALs are mounted to holes in the enclosure back. As to the strap -- the instructions do not discuss removing it, so it shouldn't be removed. – ThreePhaseEel Aug 19 '18 at 22:50

See ThreePhaseEel's answer above.

TPE is a panel master. My info is more general to panels at large, leaving it up for reference.

You're powering a shed. It's an outbuilding. That means it needs a main break-- I mean a main shutoff switch of its own. Generally the cheapest way to provide a main shutoff switch is to buy a panel with a main breaker in it. Also the most compact (as opposed to a separate shutoff switch).

That's not happening with this main-lug panel. You could backfeed a plain breaker, but hold on - Code requires bolting the breaker down so it can't tip out like a normal breaker.

Normally, when a sub needs a main shutoff switch, and you use a main breaker for that, nobody cares the breaker size. However, I note that some of ThreePhaseEel's scenarios in the other question call for tapping a much larger feeder, and that definitely requires an actual, workin-for-a-living main breaker.

With any panel, prepare for the tiedown kit to glom 2 additional spaces, as many panels have unusable space abeam of the backfed main breakers.

  • The good news is that Homelines are convertible between main lug and main breaker, and there is such a thing as a QOM60, so he can simply put the appropriate size main in and call it a day, without having to worry about eating slots due to a backfed breaker. – ThreePhaseEel Aug 19 '18 at 19:10
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    I yield to the master. That would explain the complete absence of tiedowns. Also why a 12-space panel is so large. Not deleting since you reference it. – Harper - Reinstate Monica Aug 19 '18 at 19:14

Your 60A dual pole breaker will need to be in the main breaker panel to protect the 60A rated wiring you will use to feed the sub-panel. Make sure such wiring has four conductors (2 hot, 1 neutral and 1 safety ground).

A panel with "main lugs only" will have a place to terminate the large size wires incoming into the panel. There would not be a main breaker in such panel.

The main lugs:

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  • I'll need to have a main breaker here since I'm installing a feeder off a 200A service pedestal. – isherwood Aug 19 '18 at 18:25

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