Help installing new subpanel for wall ovens


Old 04-19-15, 12:54 PM
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Join Date: Aug 2014
Location: USA
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Help installing new subpanel for wall ovens

My old 24" wall ovens are dying. One is dead and the other is giving error messages. So, I'm forced to upgrade right away to a new 27" double oven. I say "forced", because this kitchen needs a total renovation which is maybe two years off. I can't just swap the new for the old unit and use the old cable because I discovered recently that someone in a earlier rehab installed it improperly--they hard wired the ovens directly into an old screw fuse panel box mounted in the rear of one of the base cabinets at the other end of our galley kitchen layout. No fuse, no breaker for the ovens.

As long as I need to replace the ovens now, I thought I'd install it safely into a new kitchen sub-panel mounted in the cellar, ready and waiting for the new kitchen in the future.

The cabinet has enough width to fit the larger unit... and I'm great at carpentry--no problem there.... I've never installed a sub-panel, although I've done all my own electric for over 35 years, but could use some advice about the subpanel install:

Subpanel suggestions:
Subpanel must be big enough for at least 6-8 20 amp breakers and the 40 amp/220 for the ovens and am I right in thinking it should be 100 amp? Cable size... 8? Brands?

Layout of the house:
Triple brick house with stone foundation cellar under the main house... the walls are solid brick. Kitchen ell has joists under the floor but only 4-6" space between the bottom of the joists and the dirt below. There is a small break for plumbing pipes that I can use for the cable runs in the stone foundation as it meets the kitchen ell.

Subpanel placement Options:
1) to put the panel next to my main service panel (very short feed cable between them) and do ALL cable runs from there (about 60 feet away from the oven location)... that's a lot of #8 cable, no?
2) mount the subpanel against the back cellar wall which can get me within 20' from the oven location. The #8 cable run is shortened to about 40-45 feet, and all the future circuit runs would also be shorter.
3) which method is better/worse considering electrical resistance?

Snaking cable under the kitchen floor:

That's the real hassle on this job. The cabinet has a 5" drawer under the wall oven cavity... there is a back to the cabinet (looks to be 1980s vintage)... I've got full 1" thick floorboards and Lord knows how many layers of plywood and linoleum/asphalt tile/vinyl sheet goods I've got to get through... and somehow I've got to snatch a #8 cable.

The cellar under the main house is no problem... but there's 17 feet under the kitchen ell that I've got to snake cable under--with only a 5 or 6 inch clearance under the kitchen joists. I've got fiberglass fish poles to snake cable, and electric snake spools, but making the turn uphill and getting inside that cabinet is going to be a nightmare. I was thinking of cutting out the bottom of the drawer and the floor under the cabinet and then bringing the cable up into the rear of the oven compartment.

As for the rest of the kitchen circuits... I'll leave everything until the full remodeling. The cables are fine--all Romex, the fuse box is fine too-- I've rarely blown a fuse in 17 years in this house. It's just that darned cable to the oven I've got to remove and run into a new sub-panel.

Thoughts on my approach to this? Advice on the subpanel part of the job? Thanks!
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Old 04-19-15, 01:26 PM
Join Date: Mar 2006
Location: Wet side of Washington state.
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A dozen or more pictures may help to clarify your situation. I think that you need to bone up a bit on modern electrical systems.

First of all, the term "220" is long outdated. The higher residential voltage is 240 and has been for at least the last fifty years. I know that people continue to use the "110" and "220" descriptors but they are wrong.

Secondly, from your description it seems the current fuse panel is buried at the back of a lower cabinet. That is also wrong and needs to be changed.

Thirdly, number 8 copper type NM cable is limited to 40 amperes, you cannot use #8 as a feeder to a sub-panel that will have more than 40 amperes of load.

We need the manufacturer's data on the new oven units, the voltage and amperage and/or wattage before making any recommendation on cable sizes.

Lots more.
Old 04-19-15, 01:40 PM
pcboss's Avatar
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I would just pull a new cable for the oven at this time.the

It may be easier later to run any new circuits in the walls behind the cabinets during the remodel.
Old 04-19-15, 02:56 PM
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First off, although I am much older than you apparently, I do know that it's 240 and not 220... hard to break old habits (although I find myself typing it both ways). Don't know what the terminology for something I do understand has to do with my questions...

I KNOW, the fuse panel is buried and doesn't meet code. I plan to change that in the future remodel... I thought I said as much. I can't change it now because it would effectively make me rip out every cabinet and outlet along that side of the kitchen and all the walls behind the cabinets. Essentially, all things I will be doing in a year or two anyway. Besides, I think I said the wiring is safe going to that box otherwise... all romex, the outlets are fine, grounded, etc. I cannot possibly rip all that out when that's not the crucial issue at hand. We need to replace the ovens now. I will bring the new subpanel and wiring to the ovens up to code now.

As for cable sizes, I've already checked the specs... the draw for both ovens is rated 34.2 amps at 240.... #8 cable is fine for this, right? I was referring to #8 for this oven circuit. Pardon me for not being clear enough. Mia culpa. So, what cable size and type to connect a 110 amp main breaker in the sub to the main panel? Again, as I said, it's this part of the job I need advice on-specs for a subpanel... parts, cables, etc. Or, make it easy a link to a video on "Installing a Subpanel 101".

So, again, a 40 amp 240V breaker for the ovens, and about 6 - 8 20 amp circuits for everything else. That's what I have to put into a subpanel.

As for photos, I don't know what I'd take photos of that would help. The old oven in still installed. I've described that I have a way to fish cable under the kitchen floor, but it would be a b*tch. I can handle that... was just looking for perhaps some pro tips to save aggravation. Photos of the new ovens wouldn't help... sure, I have the PDFs of the installation instructions, but again. I've already given the specs.

If you can't help, that's fine. Perhaps there's someone else who can offer some friendly advice.
Old 04-19-15, 03:00 PM
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Yea... that's the basic plan. Run the new cable to the oven, BUT like I said, it was wired directly into the kitchen subpanel mounted in the back of a base cabinet. I just figured to make it safe, and to code I'd get a jump start on the electrical part of our future remodel and at least get the new oven on a new circuit in a new subpanel. I'm going to trash the existing cable that the old ovens are wired into.
Old 04-19-15, 03:38 PM
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To feed a sub panel with 100 amps (IMO which would be adequate) it will depend on the wiring method you are using. If you plan to run copper NM cable (Romex) you would need to run #2/3 with ground. If you use THHN in conduit #4-4-4-8 is good, or XHHW aluminum 2-2-2-6.

Yes, #8 is good for your 40 amp feed to the oven.

I would go option 2 for panel placement. Just remember if you run NM cable it must be protected from physical damage.

Please note the sub panel diagrams in the stickies at the top of the page.
Old 04-19-15, 03:53 PM
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,399
First off, although I am much older than you apparently...
Much older? What are you, 75? 80? I'll be 65 in June.

Don't know what the terminology for something I do understand has to do with my questions.
If you know the proper terminology why do you use outdated numbers? Often people think they know but in reality they don't. I'm just making sure that you DO understand.

Your original post was worded in a manner that lead me to think that you were gong to run a new cable from the new ovens to the existing sub-panel. That would be wrong. If I misinterpreted what you were going to do then I apologize.

What does the manufacturer's installation instructions say about two ovens sharing a 40 ampere circuit? Sometimes this is allowable and other times the manufacturer wants individual circuits for each appliance. Do these ovens take a dual voltage 240/120 circuit or a straight 240 volt circuit? Number 8 copper type NM cable is allowable for use at 40 amperes, that is not a problem.

So, what cable size and type to connect a 110 amp main breaker in the sub to the main panel? Again, as I said, it's this part of the job I need advice on-specs for a subpanel... parts, cables, etc
The sub-panel, if it is in the same building as the service panel, does not require a main breaker. Using a panel with a rating of 100 or 125 amperes is common with a lesser rated feeder in order to get enough circuit breaker spaces. I rather doubt that you need a 110 ampere feed to the sub-panel if all it is going to supply is lighting and/or convenience receptacles. Counter top receptacles and receptacles in pantries and dining rooms are considered to be "small appliance branch circuits" and code requires a minimum of two such circuits although I think the code is sadly outdated in this respect and I would never use less than three SABCs. A built-in microwave oven will require a dedicated circuit as will a dishwasher although often a garbage disposal is allowed on the dishwasher circuit. The 120 volt supply to a gas-fired range (clock, light and ignitors) may be supplied by one of the SABCs as may refrigerators although many people like the refrigerator circuit to be dedicated. Lights are never allowed on SABCs.

IF you go with a 60 ampere feeder to the sub-panel you may use #6 type NM cable although it is rated at 55 amperes. This is because the code allows you to "round up" to the next standard fuse or circuit breaker size. Using #4 cable would allow 70 amperes. If you need more power then you should probably look at some other method than type NM cable to feed the sub-panel.
Old 04-19-15, 05:04 PM
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Join Date: Aug 2014
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Thanks for that link... It really helped. I'm thinking I would install a main breaker in the sub panel anyway in the scenario where the subpanel is away from the main panel. If I install right next too the main panel I'll omit it. Thanks for letting me know about code on this.

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