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1st post so go easy :-) and hoping someone can help. I am currently investigating the feasibility of this and whether to approach an electrician on it (i.e. is it even possible without massive rework).

I have a 100Amp main panel which has a 30Amp breaker connected to a sub panel in another part of the basement. Wiring etc. all looks good and right gauge.

The sub panel used to power a small workshop but I want to add a laundry room in the basement. Additionally there is no dedicated oven circuit and as this sub panel is closest to the kitchen (underneath) I would like to run an oven circuit. All in then this equates to:

  • Lights: 15A
  • Outlets: 15A
  • Washing Machine and Dryer: 20A (it's a gas dryer currently but I would like to add future support for an electric dryer (30A)
  • Oven: 30/40/50(?)A
  • Electric Dryer (Optional!): 30A

From what I've researched this would be too much for the sub panel (if all items where on at once) as it's only a 30 amp panel. Is this right?

I my pretty sure the sub panel lights and outlets (which service a small area of the basement only) can be wired to the existing basement lights and outlet circuits which could reduce it by 2 x 15A (I think this small section was wired this way to prevent ceiling tracking. Would this make it more feasible?)

Photos (click to enlarge):

Current Sub Panel

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Main Panel

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Small Extension Panel beside Main panel

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The plot thickens lol (im ditching the oven circuit for now for ease of understanding but will likely look at full upgrade anyway)

So turns out in the sub panel off the main panel there is a cable for the dishwasher and washing machine already! So i figured as the washing machine one goes over the same area of the basement i want to move the laundry room too i could pull it down and use it but now it gets odd. It seems like (from my research) this is wired as a split phase shared neutral (as per here: Term to describe two circuits run through one /3 cable) and in the receptacle i can see an entry and exit wire so i assume the exit wire goes off to the dishwasher. The wiring in the panel is odd. There seems to be 2 double pole breakers, one is 15A/15A the other is 15A/20A! The wires are split between them. Is there any easy way these can be split back to single dedicated lines? (excuse my horrific diagram)

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    You will almost certainly want both a larger feed (wire and breaker) to the subpanel, because even one of those items (electric dryer, oven) would max out the 30A feed. But such a small feed also typically means (but not guaranteed) a very small subpanel. Upload pictures of the main panel and subpanel and the experts will tell you what to do - which may range anywhere from "new cable between the panels and start adding breakers" to "rip & replace".
    – manassehkatz-Moving 2 Codidact
    Dec 4, 2020 at 15:54
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    @manassehkatz-Moving2Codidact WOW, you said almost the exact same thing as I did at the same time! Great minds think alike.
    – George Anderson
    Dec 4, 2020 at 15:59
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    Really the only thing I would think about is upgrading your service panel. It's already over subscribed, you have multiple non-listed breakers, and at best poor circuit labeling.
    – NoSparksPlease
    Dec 4, 2020 at 16:31
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    Have you considered a service upgrade? You're thinking of adding up to 80A of load (30A dryer and maybe 50A range; I'm assuming both are gas presently), but you only have 100A service. It would be worth your time to do a load calculation for your whole house to make sure you've got enough power for what you're planning, and then ask your utility if it's possible to upgrade. Some utilities will even do the upgrade for free, since it means you will be buying more power from them, and 200A is a more standard size today anyway.
    – Nate S.
    Dec 4, 2020 at 18:08
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    Those are not "double-pole" breakers. Those are tandem breakers aka twin, duplex, cheater, double-stuff etc. There's a horribly wrong way you can use a multi-wire branch circuit with a tandem, this isn't it - they made some effort to avoid that firestarting mistake - but it's still a dangerous mess. The two involved tandems need to be replaced with a quadplex.
    – Harper - Reinstate Monica
    Dec 5, 2020 at 19:55

3 Answers 3

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Well we don’t add breakers for the total. Your example a 30 amp feed with a 30/40/50 amp oven and a dryer would exceed the load calculations for a 30 amp feeder this is true a 50 amp oven alone would trip the 30 amp breaker if both elements were on. But I could put 5ea 20 amp 120v circuits and be fine even with the total being 100 amps of 120, how could this be? The actual load is what is used in the calculation and don’t forget 30 amps at 240 is 60 amps at 120.

Now to see if you can use some of your existing gear to do what you want. Check the size of existing sub panel if it is 60 amp or greater it is likely you can upsize the wire and breaker from the main (I would keep the gas dryer).

if you go with a oven at 40a or smaller a 60 amp sub could do this with what you have listed with the gas dryer.

Where you could run into problems is the 100 amp main with gas heat dryer and oven 100 amps is a no brainer.

But convert these gas over to electric and your service will need to be upgraded here is an example of the ovens I have measured they run ~38 amps, dryers 24 amps and both of these are 240v loads so right there you are at 62 amps of true load, add another 13 for lighting and outlets (13 amps each leg) in this “small area” and you are up to 75 amps of load at that level most electricians would be adding a 100 amp sub. Is the rest of your house only drawing only 25 amps? So with all you want sure it could be done and if you want to learn and your state allows it you can add the sub.

Many states allow you to even set your main panel. With code updates a new main panel that turns your existing main into a sub may be the best route, then pull from the new main or old main to feed the new area sub. Or sub of a sub.

Your question is quite broad and I tried to give you the info needed to decide if you can do it or hire it out

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I think you already know the answer to this. While panels can be over-subscribed, what you are asking about is just too much. To put those loads on the sub-panel would probably also require upgrading the feed (wiring) and breaker from the main panel, as well as replacing the sub-panel. You didn't say how many spaces are available in the sub-panel, but I would guess not very many.

Would it be possible to put the largest loads (Range and Dryer) on the main panel? The runs might be longer, but at the end of the day, might be your least expensive option.

Pics and brands of the gear are helpful. IE: If it's zinsco panel, we'd have completely different advice! (LIKE RIP IT OUT).

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If a "30/40/50A Oven" cicuit is contemplated, a 30A panel can't supply that unless it's the only thing and 30A, not 40 or 50.

Honestly, with the amount you are proposing to provision, it seems dubious that your main panel at 100A has adequate power to spare, so you might be looking at a service upgrade if your incoming service is only 100A and you have "normal household loads" on that already.

You could quite reasonably consider a 100A subpanel, if you had power to feed it - that will (probably) require a service upgrade, and definitely require an upgrade of the wiring to the subpanel location and the subpanel itself.

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  • Agreed, I should have mentioned that in my answer as well. 100Amps isn't much these days. It would be useful to know what other loads are in the home (IE: water heater, heat pump? furnace? Baseboard heat?) a pic of the main panel would be very helpful. +
    – George Anderson
    Dec 4, 2020 at 16:10

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