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Thread: New 220 4 wire stove and old 220 three wire plug

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    DIY Junior Member Wardsweb's Avatar
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    Default New 220 4 wire stove and old 220 three wire plug

    I have started a kitchen remodel where we are replacing all the appliances. The old double ovens were 220 with a three prong plug. The new ovens are four wire. Can the four wire be wired wired into a three prong plug and use a grounding strap on the neutral at the ovens? Do I need to have the house rewired with four wires back to the mains?

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    Plumber jimbo's Avatar
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    If you have 3 prong outlets existing, then generally you can plug a new stove into that. The installation manual for the stove would give details.

    If you do any renovation, including just moving those receptacles, you would most likely be required to update to current code.

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    Electrician Chris75's Avatar
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    You should have an electrician look at them. There are certain conditions that must be met to keep them.

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    In the Trades Bob NH's Avatar
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    For existing branch circuit installations there is an Exception to NEC 250.140 that permits you to use a 3-wire cord and to connect the frame of the range to the grounded conductor (the neutral) if all of the following conditions are met:

    1. It is a 120/240-volt single phase 3-wire, or a 208Y/120-volt derived from 3-phase Y system.

    2. The grounded conductor (neutral) is not smaller than #10 copper or #8 aluminum.

    3. The grounded conductor is insulated, or if not insulated is part of a Type SE service-entrance cable and the branch circuit originates at the service panel.

    4. Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.

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    DIY Junior Member Wardsweb's Avatar
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    Thanks for the info. The house was built in 1965 and the electrical is original. The three prong receptacle has a red, a black and a green wire dedicated back to a dual breaker at the main entrance panel on the side of the house.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Wardsweb View Post
    Thanks for the info. The house was built in 1965 and the electrical is original. The three prong receptacle has a red, a black and a green wire dedicated back to a dual breaker at the main entrance panel on the side of the house.

    Huston we have a problem.

    The grounded conductor must be white

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    I think the question here is not whether he can use the (existing) neutral as a ground, but rather whether he can use the (existing) ground as a neutral. Having said that, I'm not enough of a Code scholar to say yes or no, although it strikes me that the end result is electrically, if not artistically, identical.

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    In the Trades Bob NH's Avatar
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    The conditions of the exception to 250.140 that are relevant to the third wire are:

    2. The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.

    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.

    The fact that the third conductor is reported as green indicates that it meets the first option of condition 3, which is sufficient for the exception.

    It is likely that the wire available in 1965 was either the SE cable with red, black, and spiral-wrapped grounded conductor, or the NM that was red, black, and green, or NM that was black, white, and green, or NM that was black, white, and bare.

    The green wire is obviously insulated and appears to comply with the provisions of the exception which says nothing about color.
    Last edited by Bob NH; 03-18-2008 at 07:48 AM. Reason: Correction of typo "spiral-wrapped ungrounded" to "spiral-wrapped grounded" in next-to-last sentence.

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    Licensed Electrical Contractor Speedy Petey's Avatar
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    Bob, in your example, #3 refers to the grounded conductor. NOT the grounding conductor.
    The grounded conductor is a neutral, NOT a ground.

    The ONLY bare grounded conductor allowed in this exception was one that was part of an SE cable.

    The grounding conductor, or "ground", of an NM cable, insulated or not, was NEVER allowed to be used as a grounded conductor (neutral).

  10. #10

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    Wrap white tape on each end of the green wire.

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    DIY Junior Member Wardsweb's Avatar
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    Wow I now realize I know squat about this stuff. I think my best bet would be to have an electrician come in and wire it to code. At least that way, I know it will be right and compliant with the latest safety measures.

    Thanks again guys, ya'll amaze me.

    It's one thing to know and another to know that you don't know.

  12. #12
    Retired Defense Industry Engineer jadnashua's Avatar
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    All stoves built today are built to use a 4-wire hookup: two hots, a neutral, and a safety ground. Neutral and ground are connected back at or near the panel. It is safest if there is a real ground at the appliance, rather than the neutral which could get loose, or come off, or be broken accidentally. That way, you really do have a margin of safety.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member enosez's Avatar
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    Quote Originally Posted by jadnashua View Post
    All stoves built today are built to use a 4-wire hookup: two hots, a neutral, and a safety ground. Neutral and ground are connected back at or near the panel. It is safest if there is a real ground at the appliance, rather than the neutral which could get loose, or come off, or be broken accidentally. That way, you really do have a margin of safety.
    Not to start anything, but why would a nuetral have any more of a chance to come loose or break than a ground? The ground on a 6/3 is #10 if not mistaken.

    My understanding was that in the past, before all of the bells and whistles on stoves, neutrals were not needed. It was a 220volt. Now that a 110 circuit is required in some new stoves, a neutral is needed.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    How many stoves do you know of that don't have either a lamp, or an accessory plug? Those use 110vac, so require the neutral. Only the heating elements are 220vac, not any of the peripherals. Having both a neutral and a ground gives some redundency and safety. If you lost a neutral, you might blow up some of the electronics or the bulb, depending on how it was wired since it might see 220, but...
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Quote Originally Posted by jadnashua View Post
    How many stoves do you know of that don't have either a lamp, or an accessory plug? Those use 110vac, so require the neutral. Only the heating elements are 220vac, not any of the peripherals. Having both a neutral and a ground gives some redundency and safety. If you lost a neutral, you might blow up some of the electronics or the bulb, depending on how it was wired since it might see 220, but...
    Well, back in the day they might have not had a plug or an acessory outlet. If it had a bulb, it could have been rated for 240.... just a thought.

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