100 amp Sub panel from aQO 200 Amp 2-Pole Outdoor Circuit Breaker Enclosure with QOM2200VH Breaker

Question

I have an outdoor 200 amp service disconnect (QO 200 Amp 2-Pole Outdoor Circuit Breaker Enclosure with QOM2200VH Breaker). I am trying to figure out how to run a 100 amp sub panel to a new garage that will be approx. 100 ft. away. Is there any easy way to add lugs to allow for the new service wire to feed the 100 amp subpanel?

Answer 1

You bought the wrong service equipment for that job.

What you needed was a "ranch panel" without meter

Otherwise known as an "8 space outdoor main-breaker panel with thru lugs". That's a generic term, it's not the product name of any particular thing. Expect under $200.

It has: a Main Breaker. 8 spaces of normal breaker panel. And "thru lugs" at the bottom which take all the power onward.

That same critter is also made with a meter pan built into it for around $400, that's the more proper meaning of "ranch panel". You don't want that.

So, you wire this thing up exactly the same way as the main breaker enclosure that is there now. Power from the meter goes on the breaker's main lugs, and power onward to your house goes on the "thru lugs" at the bottom of the micro-panel. The neutral-ground bond is here only. 4-wire feed to all points beyond. "MH Feeder" is your friend.

Pencil in about $250 for the wire.

You will need power company permission to pull the meter to change to this new panel. (or to be more precise, to put the meter back in and have it re-sealed). The power company may require you "pull a permit" for the swap.

Do you really need 100A?

Reason I ask is most people are just spitting out a random number that pops into their head. And 100A is nice and round, that's the only reason most people pick it.

And 100A is stupendously more power than people realize. I'm in a complex of 8 cottages right now and we all share 100A service.

The upshot is that if 90A is acceptable, it brings us to a very nice "pricing and availability sweet-spot" at #2 aluminum. It's very widely used so it's available in a variety of cable types and sizes. Increases your chance of finding something suitable in these shortage times.

If you want full-on 100A, then #1 aluminum will suffice. However you'll be more limited in choice.

There has never been any issue with the safety of heavy aluminum feeder. (15-20A small branch circuits had serious issues in the 1970s, but they weren't exactly aluminum's fault.) And anyway they changed the alloy, and the lugs you attach to will be aluminum. Aluminum lugs are "the universal donor", working well with both copper and aluminum wire due to thermal expansion differences. As with all connections, screw torque matters. (feel free to infer two other statements from my last two.)

You could pinch pennies and use #4 aluminum wire (65A, breaker at 70A; we round up here). But honestly you won't save enough money to be worth the bother.

The panel allows you to use a smaller breaker.

You install a breaker in the panel which is appropriate to the size of the feeder cable.

• 70A for #4 Al or #6 Cu (that is not UF type)
• 90A for #2 Al
• 100A for #1 Al or #3 Cu
• 125A for 1/0 Al

If you didn't have this breaker there, you would be sending 200A down the wire to the garage. That is alright, but you'd need to use 4/0 aluminum wire to do that. 4/0 costs more than #1 + the above panel.

That would give you as much as 200A at the garage, but would be costlier to run.

Nothing wrong with a 200A garage panel, though.

The single most important characteristic of the garage subpanel is number of breaker spaces. Like I say, 100A or even 90A will let you run a lot more stuff than you could ever imagine. So very likely even after you kit out everything you expect to use, time will pass and you'll want to install more stuff. You'll have the spare amps - but do you have the spare spaces?

When you're buying a panel, spaces are cheap. Get a nice big one. 30 spaces (up to 60 circuits) is not excessive. Really. It's another deal of "small savings are not worth it" deal. Even if you already mounted it, pull it off and get a really big one. You'll thank me!

Anyway, people get snagged up on "but the big panel has a 200A breaker". Doesn't matter. The panel breaker or its bus rating only needs to be >= the feeder size. So 90A feeder feeding a 200A subpanel is totally fine.

In fact if you ran 200A wire (4/0 in your case) to that 200A subpanel, you could use up to the entire 200A (provided house draws are low at the time).