Is my oven wiring safe? How can I check?

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Old 05-28-20, 05:39 AM
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Is my oven wiring safe? How can I check?

I was installing an in-wall oven at a rental property but got interrupted and had to come back the next day. The house is old and only has a 3 wire circuit -- no ground. The oven's manufacturer said to wire nut the oven's ground wire to the neutral. While I was gone, my tenant decided (against my instructions) to wire it himself, and briefly nutted the house's red and white wires together. When he turned the breaker back on, he smelled melting plastic, and turned the breaker back off. I rewired it correctly, but could still smell a faint "melted plastic" smell when I turned the breaker on. So I turned the breaker off again. How can I tell if the wiring is safe? (The oven lights up correctly now when the breaker is turned on.) Thanks!
 
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Old 05-28-20, 05:58 AM
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Was red wire from the wall wired to white wire from the wall as well? If so, breaker should have tripped right way, unless your breaker is defect.
If red wire from the wall was wired to white wire from the oven, 120V circuit (control circuit) in the oven probably is fried because this will feed 240V to 120V circuit.
 
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Old 05-28-20, 07:00 AM
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The red wire from the wall was wired to the white wire from the wall while the breaker was shut off. Then they turned the breaker on, and got the melted plastic smell. I'm not sure if the breaker tripped (I wasn't there at that time) or if they turned the breaker off. When I got back to the house, the oven was off, and the breaker was off. That's when I found the red and white wires connected. The white wire and the ground wire from the oven were nutted together, without being connected to the wall's wiring at all. It appears that the oven is OK. I'm just trying to figure out the melted plastic smell... Since I've now wired the wiring corrrectly, is the smell maybe a residual smell from when the red and white were wired together, or is there any possibility that one or both of those wires has shorted/melted somewhere other than at the actual wiring connections? If so, I don't know how to find or fix that problem. Could there be any compromised wire somewhere inside the walls? Or would any potential issue be just with the wiring in the junction box?
 
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Old 05-28-20, 07:16 AM
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"is there any possibility that one or both of those wires has shorted/melted somewhere other than at the actual wiring connections?"

Did you find any melted/damaged wire?
If the oven uses a terminal strip was it OK?

If you did not find ant damage anywhere then yes there is a possibility that the wire in the wall has been compromised.
 
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Old 05-28-20, 07:47 AM
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Yes -- Looking inside the junction box, it looks to me like the red wire got somewhat burnt (the sheathing is blackened somewhat). Also, the neutral coming from the wall doesn't have any sheathing -- it's just stranded wire -- so there was nothing to melt (except the wire itself, which isn't). If the exposed burnt red wire is where the smell is coming from, is this OK, or could there be more damaged wire inside the wall? Again, how can I figure out if there is? What would an electrician do? (PS: I do plan to wrap some tape around the exposed neutral wire before I button it up.) Thanks to all --
 
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Old 05-28-20, 08:06 AM
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The red wire from the wall was wired to the white wire from the wall while the breaker was shut off.
Also, the neutral coming from the wall doesn't have any sheathing -- it's just stranded wire
Something isn't adding up. In post #3 you mention the white wire from the wall and in post #5 you say the neutral has no sheathing (Probably meant insulation) and that it is stranded. If you have a white coming from the wall, that should be the neutral. You say the house is old so you probably have SEU cable for the circuit if there is a bare stranded conductor, but SEU cable doesn't have a white conductor. And if what you have is a 2-wire NM cable W/Grd, the bare conductor wouldn't be stranded unless it is wayyyy oversized. Not a likely scenario either.

A picture of the wiring from the wall would be helpful. If that is impossible, a picture of the markings on the cable or the cable entering the panel would be helpful.
 
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Old 05-28-20, 08:06 AM
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If the exposed burnt red wire is where the smell is coming from, is this OK, or could there be more damaged wire inside the wall?
Well at least it gives you an idea of what caused the smell so it may be the only source.
I cannot say if there is more damage.


Again, how can I figure out if there is?
The only way I know of to be 100% sure is to pull the wire.

What would an electrician do?
I cannot say as I am not a certified electrician

I can tell you what I would do but again I am not qualified.
I would disconnect the wires at the oven and at the electrical box and then using the highest ohms setting on my multimeter check between the wires. If the wire insulation has been melted odds are that there will be a resistance between the wires, They should all measure as open between them.

Also I would not be taping the damaged wires I would cut them back till you get to good insulation.

One thing to be aware of is that this is a rental so stuff you would do in your own home are often not acceptable.
Might be best to get an electrician to check this and get it documented as safe!!!!!

 
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Old 05-28-20, 08:11 AM
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What we really need to know is what gauge is the wiring and what size breaker is it on.
Wiring should not burn. If it did.... the breaker is too large for the wire or the breaker is bad.
 
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Old 05-28-20, 08:12 AM
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PS -- I'm just getting up to speed on the terminology -- I meant to say that the white wire coming from the wall is just bare stranded wire -- no insulation. All three wires from the wall (red, black, and (white) neutral, are in one old-school sheathing (kind of brown.)
 
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Old 05-28-20, 08:20 AM
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Sorry -- I just learned how to attach a picture --
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Old 05-28-20, 08:21 AM
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So, red wire from the wall and uninsulated neutral wire from the wall was connected together?
That shouldn't cause anything to burn unless your breaker is bad or the connection was poorly made (barely touching). It should have tripped the breaker right away.

Looks like you have old 10 AWG NM cable.
Is there something else attached to this? I see 3 cables there..
 
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Old 05-28-20, 08:45 AM
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Excellent picture. Shows us the fire hazard there.

You need to use a proper junction box with proper connectors.
The box needs to be larger with connectors to fasten the cables.
The ground/neutral needs to be connected to the metal box.
That old cable looks like #8 aluminum cable.
If that cable is aluminum cable.... you can't use wirenuts to connect copper to aluminum.

Junction box
 
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Old 05-28-20, 09:31 AM
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Lambition, the wall has 3 wires (black, red, and neutral) and the oven has 4 wires -- a black, white, red, and ground. The black and black are nutted, the red and red are nutted, and per the oven instructions, the white and ground are nutted with the neutral from the wall. Nothing else in the box.

Pete -- the installation manual says that the ground wire needs to be nutted with the neutrals. They don't say anything about grounding it to the box. I typically ground to a metal box too-- but every wall oven installation manual I've seen says otherwise when connecting a 4-wire oven to a 3-wire cable (US only). There must be a reason for that?

Edit: I've called JennAir for clarification on this -- they say they will get back with me.

Note -- It's a long story, but I'm actually reconnecting the same wall oven that's been there for years. (I disconnected it, but then was able to fix rather than replace it -- so I'm just trying to re-install something that was working there for 20+ years. The part that I fixed was not electronic.)

I understand that I need to correctly secure the cables to the box -- I'll do that once I'm sure that the wiring is correct. Now... I know that the stranded neutral wire coming from the wall is silver -- very likely aluminum? Either way, the instructions are saying to nut the 2 neutrals with the grounding wire, which is copper. (I'm not sure what the white wire from the oven is made of). If it the wall's neutral is aluminum, how can I do that safely?
 

Last edited by DaveW01; 05-28-20 at 10:43 AM.
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Old 05-28-20, 09:56 AM
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Note: I found another picture (below) -- there seems to be enough cable coming from the wall for me to cut it back and re-do the ends if needed... hopefully this picture helps everyone understand what I've got --

I now understand that stranded aluminum is very common on 220/240V wiring. So how do I connect it all if I'm supposed to connect the ground wire to the 2 neutrals?

PS: I don't recall -- the breaker is either 30A or 50A -- which I believe is big enough to support the oven, which draws up to 30A. (Am I correct?) It's clear that the wire coming from the wall is thicker than the wire coming from the oven.

Thanks again to everyone for your help!
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Last edited by DaveW01; 05-28-20 at 10:41 AM.
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Old 05-28-20, 10:56 AM
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Hmmm -- OK -- I may have found the answer -- based on our discussion, I called an electrician that I've worked with in the past, and he said that I can wire nut the copper ground to the aluminum neutral in this case -- I just need to squirt some Noalox into the wire nut before I do... $3 at Home Depot.

Thanks again to everyone for their help!
 
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Old 05-28-20, 11:14 AM
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Now I can see better with zoomed out picture. I thought the wire on top is another cable with black sheathing.

I can wire nut the copper ground to the aluminum neutral
Not true.
Although you can get away with that most of the time, it is actually not allowed.
You may have tinned copper instead of aluminum. Check the wire to make sure.
Electric oven should be on 30A.

Also, cables are not properly secured to the junction box.
Feeding cable should go under the clamp to secure the cable. You also need a proper size connector for the whip through a knockout hole.
 
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Old 05-28-20, 12:56 PM
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Hmm -- I know that the oven requires a 30A circuit. Is there a problem if the circuit and breaker are 50A? Or is that just some extra capacity?
 
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Old 05-28-20, 02:43 PM
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The circuit breaker is there to protect the wiring not the device.
So the wire size determines the breaker size.
If it is 10 gauge wire then it should be a 30 amp breaker.
 
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Old 05-28-20, 04:00 PM
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OK thanks -- so are you saying that I should swap out the 50A breaker with a 30A breaker in the panel? Again, I'm new to much of this -- can I just shut off the main breaker and take out the 50A and swap in a 30A?
 
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Old 05-28-20, 04:10 PM
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can I just shut off the main breaker and take out the 50A and swap in a 30A?
Yes.... that's exactly what you need to do.
 
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Old 05-28-20, 04:21 PM
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OK thanks, to everybody -- this has all been greatly helpful!
 
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Old 05-29-20, 03:15 AM
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Your electrician was wrong about using regular wire nuts and no-alox. The connection needs to be listed for use with aluminum.
 
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Old 05-29-20, 04:33 AM
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While I was gone, my tenant decided (against my instructions) to wire it himself
I hope that you had a very serious conversation with your tenant about taking it upon themselves to tamper with the wiring that they "do not own" nor "have the right to touch". In doing so they have transferred all liability to themselves.
 
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Old 05-29-20, 07:31 AM
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PCboss -- thanks for the insight. I went online to see if I could find something other than regular wire nuts that would work in this situation, and I can't. Does the wall wiring look to you like either #8 or #10 wire? If it's an 8, I can't find anything that would work. Even if it's a 10, I'm still not sure. According to the people who make AlumiConn connectors, UL Laboratories does not recognize the existence of 10-12 gauge stranded aluminum wiring -- they say it doesn't exist. They say the wiring is (must be) tin-plated copper. It also appears that the Ideal Twister Al/Cu wire nuts aren't designed to nut together three completely different types and sizes of wire -- an 8 or 10 stranded aluminum, a bare copper ground wire, and an insulated copper wire (10?). So now I'm more confused that ever. Suggestion for a connector that fits this situation?
 
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Old 05-29-20, 07:50 AM
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Note also that I'm just re-installing something that had already been installed for 10 or more years (probably at least 20) -- and there was no corrosion on the connection that combined the three wires. Again, this says to me that the silver stranded wire almost can't be aluminum. Again, I'm being told that it was never manufactured -- thus nobody markets a connector for it. Is that incorrect?
 
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Old 05-29-20, 10:05 AM
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I went online to see if I could find something other than regular wire nuts that would work in this situation, and I can't.
It really looks more like tinned copper conductors than aluminum. Look at how fine the strands are on the bare neutral. Aluminum strands wouldn't be that fine. Look at the end of those strands, the cross section, and see if you don't see that ends are copper inside the tin surface plating. If this is tin plated copper you can use wire nuts

If it is aluminum to be connected to copper the aluminum and copper conductors cannot be in direct contact, they cannot touch at all. This is where you use a small split bolt connector with a separator. Using NoAlox in a wirenut to connect aluminum to copper wiring is a real hack job, I would never hire an electrician that did that kind of work, but sadly there are some ignorant electricians in this world who will do anything to make something work even if it isn't right. That's using the label "Electrician" loosely.

Here's the split bolt you need IF the SEU cable is aluminum.

https://www.gordonelectricsupply.com...BoC__QQAvD_BwE
 
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Old 05-29-20, 10:30 AM
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OK thanks -- for the info and the link. Lots of considerations. What a can of worms!
 
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