Can I add a subpanel?

Question

Let me start off with the facts:

1. I have 125 amp service that is fed via overhead lines to a center fed panel.
2. I am maxed out on breakers, as every 110v breaker is now a tandem breaker.
3. When other homes in my area have upgraded to 200 amp service, they did not replace the feed lines. They are rated for, at least, 200 amps already.
4. My panel is exterior to the home.
5. I need a 220v (20 amp) circuit and a 110v (15 amp) circuits run to my garage.
6. Line slack is not a consideration here.

Now to my questions: Can I add a subpanel to my current panel? Or should I bite the bullet and upgrade the service to 200 amps? I can't really afford the full panel upgrade though.

I was thinking (as a layman) that I could remove one 220v (30 amp) breaker from the main panel and put in a 220v (60 amp) breaker to feed a subpanel. Then I could feed the stove (old 220v @ 30 amp) from the new subpanel, as well as the adding a new 220v @ 20 amp breaker for the new table saw. As well as add the 110v @ 15 amp circuit.

In my uneducated brain, this makes sense. But I feel like I am missing something here. Please help.

Answer 1

One of the pros will give a long detailed answer, I'm sure.

But the short answer (from reading all their long detailed answers over many months) is that provided the existing panel is in decent shape, you can replace an existing double-pole breaker with a bigger breaker for a subpanel and use that subpanel to power several circuits, as you described.

However, you should put in a really big panel - i.e., big enough that it can eventually be your new main panel. A big (like 42 space) panel might cost you an extra $100 or $150 now compared to a small panel, but will allow you to gradually move circuits over time. Moving all those circuits is the big cost, particularly if you use the opportunity to add GFCI and/or AFCI as appropriate. But this way you don't have to spend it all at once. Then once you have everything moved you make the subpanel into your main panel, add a neutral-ground bond, and get rid of the old main panel.

Since you said "I am maxed out on breakers, as every 110v breaker is now a tandem breaker.", there is no way you can add GFCI or AFCI breakers right now. While you can add GFCI at the first receptacle in each chain and get full protection, and you can add AFCI in a separate box, it is a lot easier to put in breakers. Code generally allows you to keep the old stuff as-is, but for safety's sake, as well as if you do other upgrades (e.g., bathroom or kitchen remodel), you may want and/or need to make those upgrades at some time. With a new larger (sub)panel, you can do that easily. If the existing cables won't quite reach, you can splice them inside the existing panel, with that panel eventually becoming a large junction box when the the subpanel becomes your main panel.

Answer 2

"Rule of Six" panel with some defects

There's a rule that you have to be able to cut power to a building with six breaker throws. Houses had been single main breaker, but breakers larger than 60A were prohibitively priced. So builders proposed this type of panel, with up to six of the cheaper <=60A breakers, which together are the "main breaker", rule of six. Your panel is a cheapie and only has four. (In some configurations it has five, as indicated by the label, that's why the "service disconnect" sticker is so tall). Fortunately your panel is also Murray, which is quality. I hope the builder really enjoyed the frappucino he financed by sticking you with a small panel.

The lower left of the "main disconnect" area has a 60A breaker. That powers the rest of the panel. That's right, the lower area, spaces 7-20, is already a subpanel. Too much load in that "subpanel area" will trip the 60A breaker.

Your main-breaker area is correctly configured. Your subpanel area has some defects.

• alien breakers that misfit the busses. Only the colored Murray breakers are correct; those black Cutler Hammer/Eaton BRs do not belong in this panel, are hazardous and should be replaced with Siemens/Murray, just like the panel instructions say. Total waste, the correct ones cost the same. Not even a frappucino here.
• double-stuff breakers in spaces 15 and 16 (upper right quadrant of subpanel area), that is not allowed per the panel diagram. Only full size breakers can go there, e.g. Move the big 2-pole up while changing it to Siemens.

Expect about a $35 bill on the correct breakers.

A subpanel is a grand idea

However you will want to power it out of the "main" area of the Rule of Six" (Four), as you have planned. I am not thrilled with the oven coming out of one panel and the range from the other, though. And this is a time to think about upgrades.

First, as you discussed, a service upgrade. You could plan for the subpanel to become the new main panel, perhaps indoors where it won't be insulted by painting contractors. It should be a 200A main breaker panel, and be positioned so running fat conduit to it from the meter will be easy.

Another thing to think about is generator. If you have aspirations for a generator, solar/battery system etc. it's time to look forward and see how to lay out subpanels for this, so you're not reduced to using one of those lousy "8-circuit changeover switch deals" that cost $350. It's really not far out of your way if you put your thinking cap on now.

I also trust you've heard the "Get a really big panel. No, Really big..." conversation, 42 space is literally not too much for a properly provisioned house. It's a few frappucino's today, but gives you liberty to do what you want. More kitchen circuits, done. Plug-in hybrid, easy. Hot tub, sure. Etc. There's no reason to be limited by your panel.

Lastly, tell you a secret. Your service drop is not 200A. Neither are your neighbors'. The power company didn't upgrade those. Huh!? The power company knows what drop you have, and what your electric bill is. (Also: smart meter). When they see you actually pulling more than the drop can handle, they'll come replace it.

Answer 3

If your panel is full of double breakers and you Now want to change a 30 amp breaker to a 60 amp and feed another breaker how are we to know ? You have a 125 amp service so what is your actual load? With gas appliances I have seen 3000sq ft homes in my area have plenty of power with a 100 amp service , but a few miles away no gas all electric the owner wanted on demand electric water heater upgrades his service to 400 amp very well insulated home, still not enough for what he wanted. More info is needed but I would say you need a larger service.