I'll start by saying we just bought a fixer-upper house.

I searched the topic of adding sub panels and a lot of the answers are a bit over my head so I need some advice.

My house was built in the 20's. At some point in the last several years, someone updated the electrical stuff to a familiar breaker system. The wiring looks modern and insulated and it also looks like things are grounded as far as I can tell.

What I want to do is install an electric stove which requires a 50 amp circuit in place of the deathtrap gas oven (it was old, the line to it had leaks, and I like cooking on induction.)

What I have, I think, is 100 amp service in the breaker box. The breaker box is full, no slots to add a 50 amp breaker.

So what do I do? Should I add a sub-panel? Should I yank the existing panel and put in one with more slots?

In my mind I would think I would put the heavy current circuits like A/C, Oven, and clothes dryer on the sub-panel. That's how it was in my last house.

Anything I do, I'll spend the money to have a licensed electrician to make sure it's up to code, but I want to do the actual work myself.

The house is a single family. Two stories for about 1200 sq ft and an unfinished basement. No outbuildings, garages, wells, etc. Gas Heat, Gas Water Heater. Central A/C. electric clothes washer and electric dryer. I want to install a 50 amp electric range as cheaply and safely as possible, but I want to do it right, and of course the wife wants it done right now :) I'll add pictures tomorrow, probably. Current idea is to double check the gauge of the wire that runs to the clothes dryer to make sure it's heavy enough to handle the stove and then beef up the breaker and receptacle, just to get it done fast. If we do that, we will be able to cook, but not dry clothes, so I'll be in the same place in a month or two.

Some additional information. The breaker box is a Challenger brand SLB12 (12-24)CT. 125 amp max. The Main breaker in there is 100 amps. There is already one doubled up breaker in there. I was incorrect, there is one available slot in it. Will add pics soon (they are too big for SE and I need to edit them).

  • 2
    It’s likely we can help perhaps make room in your existing panel. If you could remove the cover and take a clear picture showing the configuration inside that would be the first step. Post it here in an edit.
    – Tyson
    Jun 18, 2018 at 15:02
  • @Tyson I'll do that, thank you. Unfortunately I'll have to wait til this evening or maybe tomorrow (depends on whether the internet gods will be smiling on my house at that time ;)
    – Paul TIKI
    Jun 18, 2018 at 15:07
  • 1
    A 100 amp panel is kinda small, if you are changing to electric, I would want to upsize the main panel to 150 amps. But you may be able to put your stove and a couple of circuits in a sub but we would need the loads that are on the service, things like well pump, square footage of the home, gas heat? Water heater, dryer, is this a farm with out buildings / shop fed from the main any booster pumps or secondary pumps for irrigation. With more info we can advise the best path forward.
    – Ed Beal
    Jun 18, 2018 at 15:10
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    Ok your 100 amp panel can probably be used. First we should figure out if your existing panel can handle tandem or double stuff breakers. We will need the make & model # from the panel. This will be the least expensive way to go, by changing 2 positions to double stuff breakers this will open up room for the 50 amp double pole breaker.
    – Ed Beal
    Jun 18, 2018 at 17:40
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    I would lay the biggest subpanel possible right next to it. 42 space if not 60, panel ampacity does not matter. Run wire good for 100A from the new panel to the old, no need for a subpanel breakers, as the main breaker will suffice. Nothing wrong with oversizing panels. There is something wrong with undersizing them; you've met. It's fairly cheap to not make that mistake. A huge panel is $100 more, which is nothing in the grand scheme of things. Jun 18, 2018 at 21:22

1 Answer 1


I would start by putting a rather large subpanel as close as possible to it, probably whichever Siemens panel ThreePhaseEel recommends, or a CH or QO if space is an issue. 42+ space. Position it with an eye toward rerouting the service wiring there.

Even before that, talk to the power company about upgrade options. If a particular size is possible, get the subpanel with that main breaker, but don't sacrifice spaces to do it.

Short term, if the new subpanel is >=100A it doesn't need any main breaker at all, or even a main-panel breaker. The main breaker in the main panel will protect it. Use at least 100A wire to connect the panels, i.e. At least #3Cu or #1Al. A reason to use cheaper Al on such a short run is the lugs will be aluminum.

Having a breaker in the main panel can be avoided with a lug-breaker, which snaps in like a breaker but has only lugs.

Now, at leisure, move one circuit at a time from the old panel to the new. That's just to get away from those somewhat dodgy Challenger breakers. If wires don't reach, I typically put 4-11/16" square boxes at opportune locations to splice. Ideally metal conduit the rest of the way to the new panel, and THHN wire inside the conduit. Ideally.

With all the circuits moved over, try to straightline the subpanel straight off the bottom (switched side) of the main breaker.

Alternately, if the power company's upgrade path calls for a new meter pan, get one with a main breaker. Gut the old panel, using it only as a gutter, to the new subpanel, using wires rated for main breaker current. If that's the plan, you can use a main lug subpanel instead of a main breaker one, saving some space. 42-space main lug CHs are not that big.

  • This seems like something logical and safe. I think the electrical stuff on the outside of the house is pretty new. They just replaced the meter.
    – Paul TIKI
    Jun 19, 2018 at 19:48
  • Accepting this answer as it seems the best way for me to approach this. Thanks all!!
    – Paul TIKI
    Jun 25, 2018 at 18:33

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