Confusion about 120/240 wiring to oven


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Old 08-24-18, 08:41 AM
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Confusion about 120/240 wiring to oven

Good News is I got the cooktop installed!

Bad news is I'm confused about how the Oven was previously wired. The oven is 120/240 but was spliced into the wiring for the previous 240 cooktop and 240 wiring from the breaker. The breaker wiring was SE wiring with only 2 hots and a ground. The oven wiring that runs from the kitchen and into the junction box has 3 wire without a ground (2 hots and neutral). The neutral was connected to the ground of the SE wire.

I don't understand what is going on here. The new cooktop is now on a separate 240 only circuit, so that is a non issue.

But I'm hesitant to wire the oven back the way it was because of my confusion. If the wiring from the breaker only has 2 hots and a ground, and wiring running to the oven has red/black/white, why would they connect the neutral to the ground? Does that mean that the ground from the breaker was actually being treated like a neutral with the return voltage on the 120 side of the oven? I' haven't actually pulled the oven out to see how it is connected to the 3 wire without ground.

Thank you in advance.

Mod note: original thread on cook top wiring..... Help-with-cook-top-wiring-please
 

Last edited by PJmax; 08-24-18 at 02:08 PM.
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Old 08-24-18, 12:24 PM
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I thought you were running a new 4 wire feeder for a new oven. Older stoves were on a three wire feeder and used what's known as an ungrounded plug/outlet. On those stoves/ovens the neutral was bonded to the frame and also acted as the ground. If the oven is a new hardwired unit it should be wired per the manufacturers specs which should be a 4 wire circuit if its 120/240V.

Edit: I went back and read your other post. I see the oven is the existing oven and was likely wired as a 3 wire circuit as I stated where the neutral is bonded to the frame. New code does not allow that anymore. When wiring is changed/altered it should be brought up to current code which is 4 wire for a 120/240V oven. I believe technically you are grandfathered and can hook the old oven back the way it was with the 3 wire where the neutral is bonded to the frame.
 

Last edited by pattenp; 08-24-18 at 12:40 PM.
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Old 08-24-18, 02:09 PM
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Thanks Pattenp! It's by no means a "newer" oven, but it is definitely newer than the cooktop was (which was straight from the 70s). The oven is a magic chef 9512wua. I found a diagram of how it was probably wired in the installation guide here https://www.searspartsdirect.com/par...f-parts-manual.


In the image is says that bare and white from the stove are wired to the neutral incoming . I guess my concern is that while i have 10 feet of black/red/white wire going to the stove (which would match this instructon), that white wire is connected to a bare wire (black/red/bare service entrance wire) running back to the circuit breaker. Is that bare wire just considered a neutral running the 120, and there is no "ground"? And since it is sitting in a metal junction box, is anything supposed to be grounded?

Thanks again.
 
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Old 08-24-18, 02:55 PM
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that white wire is connected to a bare wire (black/red/bare service entrance wire) running back to the circuit breaker.
With SE cable, bare wire is used as neutral and doubles as ground.
SE cable is the only type of cable 3 wire connection was allowed, yet I have seen regular 10-2 or 8-2 NM cables used on dryers and ovens and bare ground wire acting as a neutral. This was never allowed.

Now, 3 wire connection is not allowed even with SE cable.
 
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Old 08-25-18, 05:05 PM
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SE cable is the only type of cable 3 wire connection was allowed,

Actually, 8-3 plain NM cable and 6-3 plain NM cable was the most common 3-wire range circuit prior to 1996 when the code changed to require a 4-wire circuit. SE cable was the only type wiring where a bare conductor could be used as a neutral. For a dryer 10-3 plain NM cable was used.

I have seen regular 10-2 or 8-2 NM cables used on dryers and ovens and bare ground wire acting as a neutral. This was never allowed.

Very true. I just recently saw a home built about 2000 that had 10-2 NM cable used for the dryer circuit. Sad, very sad.
 
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Old 08-25-18, 05:38 PM
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One more thing....

First off, I really appreciate the knowledge in these forums and everyoneís help.

How do I house this connection with the white neural running from the kitchen and the bare wire from the SE wire from the breaker box? Metal box or plastic? If metal, how do I ground the metal box?

thank you
 
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Old 08-25-18, 06:13 PM
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How do I house this connection with the white neural running from the kitchen and the bare wire from the SE wire from the breaker box? Metal box or plastic? If metal, how do I ground the metal box?
Are you extending the cable? I thought you were connecting the cooktop at the same place.
Technically, you are not allowed to extend 3 wire connection and must run new 10-3 with ground from the breaker panel. If you cannot do that, at least extend the cable with SE.
I you meant neutral running from the cooktop, then just connect ground and neutral together to the bare wire.
One issue here is SE cable is usually aluminum and you are not allowed to connect aluminum to copper directly.

Use something like these and a large heat shrink tubing or wrap it with electric tape.
https://www.homedepot.com/p/2-STR-to...2-10/100172350

https://www.homedepot.com/p/Blackbur...-100151936-_-N


Actually, 8-3 plain NM cable and 6-3 plain NM cable was the most common 3-wire range circuit prior to 1996
I knew they existed, but never seen in DC area for some reason and forgotten about them. All I have seen are SE cable and 10-2 or 8-2.

Found 8-2 wired for dryer just few days ago in an apartment. Even worse, it is a sub panel with 4 wire feed (since it is an apartment) and ground wire was connected to the ground bus. Something happens to the ground feed to the panel, every grounded chassis can become hot this this unit and the units down the line.
Another funny thing is, the cable to range oven is 6-3 with ground and wired correct at the panel, but has 3 prong receptacle.
 
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Old 08-25-18, 07:05 PM
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Let me see if I can tell the story as there is a couple things going on. Iím pretty sure the original wiring was FUBAR, which is why this is so confusing to me, and Iím making it confusing to others.

Old hookup - SE wiring from breaker box (40 amp double pole). In a junction box 10-3 was run to the old 240 cooktop, and another 10-3 Was run to the 120/240 wall oven. The 3 blacks were together, the 3 reds were together, and the 2 whites from both 10-3 were wire nutted with the bare conducter from the SEU wire. I donít know how this lasted 20+ years.

Now Cooktop - new cooktop is 40 Amps by itself. I replaced the 10-3 that was running to to the old cooktop with 8-2. So I have 8-2 with ground connected to the old SEU wire. (ground tied into the bare conducter of the SEU and grounded in metal junction box). That is now on its own 240 circuit, same 40 amp double pole breaker. This was the instruction I got in original post. Is this not right?

Now wall oven - same old 120/240 wall oven with the same 10/3 wire running to basement. I had an old dryer outlet on its own 40 amp double pole circuit that was not being used. That was run with identical SEU wire too. So I took the wire out to hookup with the wall oven, so the wall oven would be on its own circuit, not with the new cooktop. That is where I am now. Can this be done? If so how should I make that connection. Could a metal box be used there without a ground? (Since the bare conducter is tied into the neutral of the 10/3, making it a 120/240 circuit)
 
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Old 08-25-18, 07:27 PM
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I replaced the 10-3 that was running to to the old cooktop with 8-2. So I have 8-2 with ground connected to the old SEU wire.
Correct as long as you have used correct type of connectors and your cooktop is 240V only.
If your cooktop is 120V/240V then it is wrong.

I had an old dryer outlet on its own 40 amp double pole circuit that was not being used. That was run with identical SEU wire too. So I took the wire out to hookup with the wall oven, so the wall oven would be on its own circuit, not with the new cooktop. That is where I am now. Can this be done? If so how should I make that connection. Could a metal box be used there without a ground? (Since the bare conducter is tied into the neutral of the 10/3, making it a 120/240 circuit)
Technically, you cannot do that. It will work if you tie both neutral and ground to bare wire, which is neutral in SE cable. However, it is not to the code.
The correct way is to run 10-3 all the way to the breaker panel.
 
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Old 08-25-18, 07:51 PM
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Thanks!

There is no ground in the 10-3 running to the wall oven. It is only red/black/white. Iím guessing the ground and neutral from the actual oven was tied into just the neutral of the 10/3, which was in the instruction Manuel for the oven from 20 years ago.

So that is my current dilemma. Black/red/white 10-3 wiring connected to black/red//bare SEU. When connecting that point, do I do it in a plastic box or metal box. And if metal, how do I ground the metal box, since there is no specific ground in the wiring?

I understand it probably all just needs to get upgraded to 4 wires... and that is the plan when it is time to get a new wall oven

appreciate the help
 
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Old 08-25-18, 08:25 PM
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There is no ground in the 10-3 running to the wall oven. It is only red/black/white.
That is a old 10-3 cable without ground. While it is the correct type of cable for 3 wire connection, it is no longer allowed. You can keep the existing wiring as is, but you have to follow the current code when it is modified.


So that is my current dilemma. Black/red/white 10-3 wiring connected to black/red//bare SEU.
That will work and no more dangerous than what you had before. However, still a code violation since you are modifying.


When connecting that point, do I do it in a plastic box or metal box. And if metal, how do I ground the metal box, since there is no specific ground in the wiring?
You can use either one. Ground can be connected to neutral wire.

https://www.homedepot.com/p/1-0-to-1...B2-5/100172941

Using one of this will make things easier when using metal junction box. Just screw it down to the junction box using ground screw.
 
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Old 08-25-18, 09:41 PM
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Fantastic. So use one of those duel connecters for the SE bare and the neutral and mount it with a ground screw. I can still use a wire nut on the reds and blacks since they are all copper?

thanks for your time and assistance!
 
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Old 08-25-18, 09:49 PM
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Also - for education purposes... you say itís no more dangerous than I had before? Obviously I needed to split the two to two switches with the amperage of the new cooktop, but the before 240 cooktop and the 120/240 wall oven sharing the bare SE wire was ďokĒ?

seems like there was some bad electrical work. I wonít even bring up that the wires were laid across furnace ducts and insulation from the 10-3 to the old cooktop was showing bare metal!

I got all that stapled to the joists, but I feel lucky that I explored this when I did!
 
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Old 08-26-18, 06:07 AM
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I can still use a wire nut on the reds and blacks since they are all copper
SEU cables are usually aluminum. Aren't yours? If it is you need to use something like below and wrap it with electric tape.

https://www.homedepot.com/p/1-0-STR-...2-10/100126602

https://www.homedepot.com/p/Blackbur...B1-5/100151936

or just use insulated connector like below. (Expensive, but the best)

https://www.homedepot.com/p/Polaris-...T-4B/303577920


before 240 cooktop and the 120/240 wall oven sharing the bare SE wire was ďokĒ?
Not ok. Forgotten about 2 10 AWG cables connected together. I was talking about 3 wire connection using neutral as ground.
 
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Old 08-26-18, 08:43 AM
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I think you are right. I will have to use these

https://www.homedepot.com/p/1-0-STR-...2-10/100126602

Hopefully last question, and probably a stupid question, with having 2/3 of these pushed into one box, do I have to worry about the metal connecters touching other connecters or the box themselves?

thanks!
 
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Old 08-26-18, 09:44 AM
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Actually, 8-3 plain NM cable and 6-3 plain NM cable was the most common 3-wire range circuit prior to 1996

I knew they existed, but never seen in DC area for some reason and forgotten about them. All I have seen are SE cable and 10-2 or 8-2.

Back in the 1970s NM cable plain or without ground was widely available here. I have seen 14-2, 14-3, 12-2, 12-3, 10-2, 10-3 as well as 8-3 and 6-3 all sold as plain or without ground. I assume the smaller sizes were sold for extending ungrounded circuits back then. Up until the code changed in 1996 it wasn't uncommon to see 10-3 w/G used to feed a 3-wire dryer receptacle or 8-3 or 6-3 w/G to feed a 3-wire range receptacle. I am not sure when manufacturers stopped making NM cable without a grounding conductor, but think it was sometime in the early 1980s.
 
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Old 08-26-18, 10:16 AM
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Lambition - it looks like the SE Wire is copper clad aluminum on the 2 hots. Would the strands of bare wire be copper clad to? They look copper but since the strands are so thin, I canít tell.

I think I got it

being copper clad, I would still use the metal splicers to connect the 10/3 and the SE CABLE on the hots, and the metal splicer with grounding screw for the neutral and bare wire from SE cable? And then ground that to the metal box. If the braided bare is all copper, it wouldnít hurt to connect two coppers with the metal splicer. Do I have this right?

my question from above is still open about these metal splicers. Can they inadvertently touch each other or the metal box?

thanks so much!

 
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Old 08-26-18, 11:53 AM
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NM about the question about the set screw splicers touching each other, I missed where you said to wrap in electrical tape
 
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Old 08-26-18, 03:14 PM
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do I have to worry about the metal connecters touching other connecters or the box themselves?
Wrap it with electric tape or heat shrink tubing.
For a split bolt, it is best to wrap it with rubber splicing tape first, then wrap it with electric tape. The reason is the splitbolt has sharp edges and electric tape alone may not be enough.
Rubber splicing tape does not stick very well and may come undone, therefore, should be wrapped with electric tape to finish.

When wrapping with electric tape alone make it thick.

Also use a biggest junction box you can fit the space. It is hard to fit the splice in a regular 4x4 junction box and if the wires are pushed tight against sharp edges of the junction box, it will eventually cut through to insulation.
4x4 junction box with a box extension probably will give you a good space.
 
 

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