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

  1. #16
    Retired Defense Industry Engineer jadnashua's Avatar
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    Ever tried to buy a 240v light bulb...not in your everyday store! If they had a bulb, oven light, night light, indicator light, etc., they were powered off 110. When I was in the Army, we had one shelter with both 28vdc and 110vac lighting. The bulbs were the same style. If you weren't careful, the 28V bulbs work great as flash bulbs! Working the other way, they worked more like a candle, which isn't catastrophic, but kind of useless.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  2. #17
    In the Trades Bob NH's Avatar
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    Notwithstanding all "The sky will fall on your head" remarks, the National Electrical Code explicitly permits, for existing branch circuit installations, "the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlets or junction boxes that are part of the circuit for these appliances" to be grounded to the grounded circuit conductor if all of the conditions that I posted earlier are met.

  3. #18
    Electrical Contractor/Instructor jwelectric's Avatar
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    A couple of red flags come to surface with this installation and the insulated GREEN conductor raises a flag to its highest.

    If this circuit installation has an insulated green conductor it must be wired with some type of cord. I all my years I canít remember seeing a SE cable or NM cable that had an insulated green conductor that came installed in the cable. The use of a cord as a permanent wiring method is a big no no.

    If this installation is done in some sort of metal jacketed cable such as MC or AC then the use of a three wire receptacle is NOT allowed.

    In the end the one thing to remember is that if a three wire receptacle is used then any and all exposed metal of the range will be at the same potential as the conductor carrying the unbalanced load.
    In other words the exposed metal will be at a potential of 120 volts anytime that the clock or oven light is energized.
    Last edited by jwelectric; 03-19-2008 at 11:55 AM.

  4. #19
    In the Trades Bob NH's Avatar
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    Quote Originally Posted by jwelectric View Post
    In the end the one thing to remember is that if a three wire receptacle is used then any and all exposed metal of the range will be at the same potential as the conductor carrying the unbalanced load.
    In other words the exposed metal will be at a potential of 120 volts anytime that the clock or oven light is energized.
    That (the bolded part of the quote) is just plain WRONG. It will be at a potential equal to the voltage drop in the ungrounded conductor that arises from the IR drop of the unbalanced current, which is the same condition that has existed on ranges, ovens, and dryers for as long as they have had lights and clocks.

    With 1 Amp which would be typical of a light, and a 50 ft run to the panel, the potential will be about 0.06 Volt, about 1/25 of the voltage of an alkaline battery. Even if the there were a 100 Amp dead short to the grounded conductor, which would quickly trip the breaker, the voltage would be about 6 Volts which is far below the hazardous level.

  5. #20
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Bob NH View Post
    That (the bolded part of the quote) is just plain WRONG. It will be at a potential equal to the voltage drop in the ungrounded conductor that arises from the IR drop of the unbalanced current, which is the same condition that has existed on ranges, ovens, and dryers for as long as they have had lights and clocks.
    It has been a long day trying to bring my current classes up to the 08 code cycle.

    The touch potential would put the person in parallel with the clock and or light. In other words the person could become a parallel path with the current these items draw.

    Touching the frame of the range and such items as grounded crock pots made from stainless steel to large bowl mixers could lead to a shocking experience.

    Thanks Bob for keeping me straight.

  6. #21
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by Bob NH View Post
    Notwithstanding all "The sky will fall on your head" remarks, the National Electrical Code explicitly permits, for existing branch circuit installations, "the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlets or junction boxes that are part of the circuit for these appliances" to be grounded to the grounded circuit conductor if all of the conditions that I posted earlier are met.
    Exactly. And the GROUNDED circuit conductor is the neutral. The "ground" is the grounding conductor.
    Big, BIG difference.

  7. #22
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Speedy Petey View Post
    Exactly. And the GROUNDED circuit conductor is the neutral. The "ground" is the grounding conductor.
    Big, BIG difference.
    Yea what Petey said and the green conductor can not be used here, period

  8. #23
    DIY Junior Member Wardsweb's Avatar
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    Followup: the old wiring was removed. Good thing too, as it was aluminum. Nice new correct wire run and new recepticle installed. Like my father always told me, "there is only one way to do it...the right way."

  9. #24
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    Default thanks for the clarification

    Quote Originally Posted by Bob NH View Post
    That (the bolded part of the quote) is just plain WRONG. It will be at a potential equal to the voltage drop in the ungrounded conductor that arises from the IR drop of the unbalanced current, which is the same condition that has existed on ranges, ovens, and dryers for as long as they have had lights and clocks.

    With 1 Amp which would be typical of a light, and a 50 ft run to the panel, the potential will be about 0.06 Volt, about 1/25 of the voltage of an alkaline battery. Even if the there were a 100 Amp dead short to the grounded conductor, which would quickly trip the breaker, the voltage would be about 6 Volts which is far below the hazardous level.
    good advice - my search got to this forum because I replaced an oven - both the new and old units had the neutral "white" cable bundled with the grounding "bare copper" cable running about 10 feet to the service box - I had heard that this was out of code and that I should change the wiring to a 4-wire set from the service box - but I had also heard it was a minor, non-critical issue

    after reading this, i thought just rewiring it as before would probably be OK - I consulted with an electronics engineer friend who confirmed that, yes, sending an energized neutral into the grounding path is only very slightly risky - he did the math and said we should wire it up, apply power and test the unit with a voltmeter - sure enough, voltage between the oven frame and the kitchen sink is .7 volts

  10. #25
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by lotus View Post
    good advice - my search got to this forum because I replaced an oven - both the new and old units had the neutral "white" cable bundled with the grounding "bare copper" cable running about 10 feet to the service box - I had heard that this was out of code and that I should change the wiring to a 4-wire set from the service box - but I had also heard it was a minor, non-critical issue

    after reading this, i thought just rewiring it as before would probably be OK - I consulted with an electronics engineer friend who confirmed that, yes, sending an energized neutral into the grounding path is only very slightly risky - he did the math and said we should wire it up, apply power and test the unit with a voltmeter - sure enough, voltage between the oven frame and the kitchen sink is .7 volts

    And how much current or amperage was on this path?

    Remember it is not voltage that does harm but amperage that kills!!!!!!

    Find yourself a new electronics friend before this one gets you killed.

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