3wire house vs. 4wire range

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difowler1

Senior Member
I am trying to find the article about installing a new 4 wire range in a house with a 3 wire circuit, but I can't find the rules I need tonight.

I have 2 hots and one ground. The code on 250.140 has extensive comments on installing a new 4 wire range where no equipment grounding conductor is present.

The more common scenerio is where you have 2 ungrounded conductors and 1 grounding conductor. How do you hook that up to a 4 wire new range? Anyone know the article?
 

Dennis Alwon

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Location
Chapel Hill, NC
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Retired Electrical Contractor
I am trying to find the article about installing a new 4 wire range in a house with a 3 wire circuit, but I can't find the rules I need tonight.

I have 2 hots and one ground. The code on 250.140 has extensive comments on installing a new 4 wire range where no equipment grounding conductor is present.

The more common scenerio is where you have 2 ungrounded conductors and 1 grounding conductor. How do you hook that up to a 4 wire new range? Anyone know the article?

There is no code on that. You either rewire the range circuit or use a 3 wire range cord.
 

hurk27

Senior Member
Usually the instruction with the range will tell you how to convert from a 4-wire to the 3-wire, but if you get a case where a home owner moved out of a newer house into an older house you might not have access to these instructions, but it is rather simple, when you go to change the range cord, you will see a copper strap from the frame by the neutral terminal, this strap is to bond the case to the neutral, on some ranges it might be a white or green wire, but never hook up a dryer or range to a 3-wire circuit without bonding this, as if you only hook up the ground and hots, you can fry the electronics, ranges and dryers are both a 120 volt load and a 240 volt load, and floating the neutral can cause problems, not so much on a dryer as a range, but not a good idea just the same.

250.140 is an exception, and only if you have met all 4 (1 thru 4) requirements, this 3-wire circuit can not originate at a sub panel, you can not have NM feeding it, are some of the things that get over looked that are not allowed under this exception, this is a very dangerous install because a lost neutral will cause 120 volts to be on the frame of this range, so make sure you do these by the book.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
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Electrical Contractor
250.140 is an exception, and only if you have met all 4 (1 thru 4) requirements, this 3-wire circuit can not originate at a sub panel, you can not have NM feeding it, are some of the things that get over looked that are not allowed under this exception, this is a very dangerous install because a lost neutral will cause 120 volts to be on the frame of this range, so make sure you do these by the book.

Wayne, this is only true if the using type SE cable with a bare neutral. If all conductors are insulated it can be fed from a sub.

If the existing circuit only has 2 hots and an equipment grounding conductor there is no compliant way to connect a range that requires a neutral conductor.
 

hurk27

Senior Member
Wayne, this is only true if the using type SE cable with a bare neutral. If all conductors are insulated it can be fed from a sub.

3) The grounded conductor is insulated, or the grounded
conductor is uninsulated and part of a Type SE service entrance
cable and the branch circuit originates at the
service equipment.

I have alway been told that because of the "or" between the two sentences, the "and the branch circuit originates at the
service equipment" applies to both sentences?

If the existing circuit only has 2 hots and an equipment grounding conductor there is no compliant way to connect a range that requires a neutral conductor.

I agree with this as I stated in my post that NM is one of the more over looked violations of a 3-wire install.
Although I have seen MC with an insulated grounds used, and it wouldn't raise a flag to me since it is insulated, I agree it is bending the code.
 
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curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
I have always been told that because of the "or" between the two sentences, the "and the branch circuit originates at the
service equipment" applies to both sentences?

I have never heard it interpreted that way. The originating at the service equipment requirement only applies if you are using a bare neutral in a type SE cable.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
What I also wondered is why it had to be part of an seu cable. If seu could be used at the main panel why not NM. I know it is not compliant but why. I am guessing the neutral in the seu is larger than the egc in nm cable.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
Dennis, I don't this there would be any difference with modern NM cable but older NM had a very small EGC which was never intended to be a current caring conductor.
 
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