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  1. #11
    Join Date
    May 2008
    Location
    Pacific Northwet
    Posts
    1,356

    Default Re: changing 3wire 240v to 4wire 240v

    Quote Originally Posted by TomF View Post
    Years ago I ran No. 10 copper wire, three conductor (white, black and uninsulated ground) from the breaker panel to an electrical dryer which we still use.

    In the panel I connected the white wire to one side of a double pole breaker and the black wire to the other. The ground wire I connected to the ground bus. I'm pretty sure the service neutral is connected to the ground bus in the breaker box.

    The other end of the wires I connected to an electic dryer with the white and black wires going to the heating element and the ground wire to the metal case of the dryer.

    Is this a dangerous hookup? Should I have used a 4-wire conductor and somehow connected this at the dryer and breaker box end?

    I'm asking because the new wall oven I am thinking of connecting, came with instructions that say this:

    "The neutral of this unit is grounded to the frame through the green or solid grounding wire. (The green and the white wires are twisted together at the termination of the conduit.) If used on new branch-circuit installations (1966 NEC)...or in an area where local codes prohibit grounding through the neutral conductor, untwist or disconnect the green wire and connect the green wire to ground in accordance to local code. Connect the white neutral to the service neutral."
    You may connect a range or dryer using and EXISTING 3-prong cord-and-plug disconnect (in the past this was an acceptable method). In this case, the neutral in the appliance is bonded to the frame and a single grounded conductor is used for both ground and neutral. However, the grounded conductor in the cable must be the same size as the current-carrying conductors.

    In any NEW installation, you must use a 3-wire-plus-ground cable and a four prong receptacle. When installing the pigtail cord, you must ensure that the neutral and ground/frame are NOT bonded together.

    In the case of a built-in range, stovetop, or oven unit, the principle is the same; ONLY if the existing wiring only has two hots and a ground may the neutral and the ground/frame be connected; otherwise (existing 3 wire plus ground or new installation) you must have separate ground and neutral running to the appliance.

    In no case in current code is combined neutral and ground acceptable EXCEPT for existing wiring and service entrance conductors.

    In the case of the hot tub, I suspect that the existing wiring either was not originally for a hot tub or was incorrectly installed. It should be supplied with a 3-wire-plus-ground 120/240V service and GFI protection.

  2. #12
    Join Date
    Mar 2009
    Location
    Davis, CA
    Posts
    1

    Default Re: changing 3wire 240v to 4wire 240v

    If the difference between the 3-wire and 4-wire 240v is the ground; is it possible or acceptable to just add a grounding wire run from a nearby circuit instead of having to run replacement wire all the way back to the panel?

  3. #13
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,557

    Default Re: changing 3wire 240v to 4wire 240v

    Quote Originally Posted by bgstein View Post
    If the difference between the 3-wire and 4-wire 240v is the ground; is it possible or acceptable to just add a grounding wire run from a nearby circuit instead of having to run replacement wire all the way back to the panel?
    3 wire 240v can be 2 hots and a neutral or 2 hots and a ground. If it is 2 hots and a neutral then a seperate ground wire can be run.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

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