A friend just bought a new in-wall oven. It accommodates whichever type of plug is required - meaning it comes with no plug at all.

Her house is over 20 years old, so I expect to find a NEMA-10 receptacle in the wall where the old oven is plugged in. Current practice and code is apparently to use a NEMA-14-50 receptacle. I will update and replace the receptacle if there is a ground conductor available.

Here's the question: Is their any reasonable chance that there is an unused ground connector already at the old NEMA-10 receptacle? If I find an uninsulated copper wire there, is it OK to use that as the ground for a NEMA-45-50 receptacle?

If putting a new receptacle there is too big a pain, I'll just slap a NEMA-10 plug on the new oven and never think about it again. But I'd like to do the update if it's not too big a deal.

 

If I find an uninsulated copper wire there, is it OK to use that as the ground for a NEMA-45-50 receptacle

The easiest way would be to look in the breaker box, to see if the existing cable has the ground.

 

The easiest way would be to look in the breaker box, to see if the existing cable has the ground.

Maybe. It may not be so easy to trace the cable all the way to the breaker, depending how crowded the box is. But I will want to look at the breaker anyway and it'll be easy enough to take a look.

 

From my experience it is usually easier to look in the breaker box than to remove and replace the outlet. Then replacing the outlet while a new one is bought. And just because the outlet has a ground wire present it still would need to be checked in the box to see if it was/is connected there.

Wouldn't the stove be one of the only 220V circuits in the box? And should be a "stand alone" circuit, with nothing else on it.

 

Wouldn't the stove be one of the only 220V circuits in the box? And should be a "stand alone" circuit, with nothing else on it.

I would expect so, yes. I'll take a look. If the ground wire isn't already there, I won't even raise the issue to the homeowner.

 

I've worked on a lot of old rental houses over the years for people and have learned to do things without spending much money or time.

 

I've worked on a lot of old rental houses over the years for people and have learned to do things without spending much money or time.

Good news bad news. My friend's old oven had 4 conductors going to it. The ground is uninsulated and lower gauge than the red/black/white, but it's there.

The bad news is that there was no receptacle - it was wired straight it and I had to cut them, with great difficulty, just to get the old oven out. I felt like I was in one of those bad action movies where I disarm the bomb by reaching into a dark crevice as far as I can and try to cut a thick wire without being able to see it while cutting.

This is what's left. Wondering what to install to make the new connection.

 

I'd shorten the BX sheath a little, To get enough wire to work with, and install an outlet box the size that is needed to fit the new receptacle. Just the first one that came up, not really what to buy, it's a case of 10 - https://www.homedepot.com/p/Carlon-...gclsrc=aw.ds&dclid=CNrh0Yu3id4CFVEMNwodVuEE6Q

 

On the new oven the nameplate data should list the current? The reason I ask is because in the picture you posted the BX cable looks a little small so I am wondering what the wire gauge is? The red, black and white just look to be around maybe AWG 12 which is fine up to 20 Amp service. Wondering what runs from oven to circuit breaker panel as to wire gauge? The NEMA 14-50 is a 50 Amp rated service receptacle and depending on the run length you would be looking at AWG 6 wire. Depending on the oven you may be fine with a NEMA 14-30 which is for 30 Amp service and AWG 10 wire in most cases and is less costly.

Ron

 

On the new oven the nameplate data should list the current? The reason I ask is because in the picture you posted the BX cable looks a little small so I am wondering what the wire gauge is? The red, black and white just look to be around maybe AWG 12 which is fine up to 20 Amp service. Wondering what runs from oven to circuit breaker panel as to wire gauge? The NEMA 14-50 is a 50 Amp rated service receptacle and depending on the run length you would be looking at AWG 6 wire. Depending on the oven you may be fine with a NEMA 14-30 which is for 30 Amp service and AWG 10 wire in most cases and is less costly.

Ron

It’s at least 10 AWG. I just used 12 in a project and these are noticeably stiffer. The appliance whips at Home Depot were mostly 10 when I looked today, so I suppose that’s probably what it is.

I was mislead about how the oven is configured. There is no plug or cable, only another whip like the one in the picture. So my new plan is to add a box and connect the two whips together in it. No plug or receptacle. I’d eliminate the old whip if I could but the house had additions that make that nearly impossible.

 

I'd shorten the BX sheath a little, To get enough wire to work with, and install an outlet box the size that is needed to fit the new receptacle. Just the first one that came up, not really what to buy, it's a case of 10 - https://www.homedepot.com/p/Carlon-3-1-2-in-Hard-Shell-Old-New-Work-Ceiling-Box-Case-of-24-BH614R/202217024?cm_mmc=Shopping|G|Base|D27E|27-6_CONDUIT-BOXES-FITTINGS|NA|PLA|71700000034238990|58700003946879308|92700031954573787&gclid=EAIaIQobChMI0PnXg7eJ3gIVkIjICh3wNwy-EAQYBSABEgKfp_D_BwE&gclsrc=aw.ds&dclid=CNrh0Yu3id4CFVEMNwodVuEE6Q

Yup, that’s pretty much the plan except as detailed in #10.

 

It’s at least 10 AWG. I just used 12 in a project and these are noticeably stiffer. The appliance whips at Home Depot were mostly 10 when I looked today, so I suppose that’s probably what it is.

I was mislead about how the oven is configured. There is no plug or cable, only another whip like the one in the picture. So my new plan is to add a box and connect the two whips together in it. No plug or receptacle. I’d eliminate the old whip if I could but the house had additions that make that nearly impossible.

That should work fine.

Ron

 

A friend just bought a new in-wall oven. It accommodates whichever type of plug is required - meaning it comes with no plug at all.

Her house is over 20 years old, so I expect to find a NEMA-10 receptacle in the wall where the old oven is plugged in. Current practice and code is apparently to use a NEMA-14-50 receptacle. I will update and replace the receptacle if there is a ground conductor available.

Here's the question: Is their any reasonable chance that there is an unused ground connector already at the old NEMA-10 receptacle? If I find an uninsulated copper wire there, is it OK to use that as the ground for a NEMA-45-50 receptacle?

If putting a new receptacle there is too big a pain, I'll just slap a NEMA-10 plug on the new oven and never think about it again. But I'd like to do the update if it's not too big a deal.

Why does it has to be unused? Whats wrong with a standard grounding cable?

You can always put a grounding stick in the yard or somewhere(its a house) and make sure noone touches it.

 

Whats wrong with a standard grounding cable?

Running new wires is not an option. I have to deal with whatever is already there. Fortunately, I've discovered that there is a ground wire.

 

Running new wires is not an option. I have to deal with whatever is already there. Fortunately, I've discovered that there is a ground wire.

With that in mind as long as existing will support the load of the new over no problem. Since it is only an over it likely only has a bake and a broil element. If the existing is AWG 10 240 VAC 3 wire with ground you are good for 30 Amp service. Most I have seen have been between 2 and 5 KW and have a maximum current of about 21 amps on about a 5 KW unit. Your plan should work out fine.

Ron

 

With that in mind as long as existing will support the load of the new over no problem. Since it is only an over it likely only has a bake and a broil element. If the existing is AWG 10 240 VAC 3 wire with ground you are good for 30 Amp service. Most I have seen have been between 2 and 5 KW and have a maximum current of about 21 amps on about a 5 KW unit. Your plan should work out fine.

Ron

Yup, it's done and all is good. The whip that came with the new oven was much thinner wire than the old whip (pictures, which was 10 gauge as I thought). I'm not sure the new one was even 12 gauge but maybe it was. Both whips were stranded except for the ground wire in the old one. Anyway, I joined them together with wire nuts inside a new box. Ground wires were joined to the box.

I was able to get below the false bottom propping up the oven and place the box there, and then pull excess whip down into that space as we pushed the oven into place. Darned if the thing didn't fit without hardly any fiddling around. Flipped the breaker, set the clock, declared victory and ran away.

 

Yay, a happy ending!

Ron