Confused on the wiring for stove and dryer transfer to new house

Discussion in 'Electrical Forum discussion & Blog' started by James23912, Apr 14, 2021.

  1. James23912

    James23912 Member

    Joined:
    May 16, 2020
    Location:
    Vermont
    So I am moving into the new house this weekend from circa 1992 trailer, which has 3 wire main while new place is 4 wire,( counting ground), so I have been assuming I would need to change the cords on the stove and dryer but I did not look at them beforehand, so I bought new ones at Home Depot yesterday and just now went to move the dryer and was surprised to see it has the same 4 prong cord and outlet as the new one I bought , the dryer and stove are both at least a few years old, both bought used. The stove plug also has 4 prongs, so I don't understand why the old wiring is this way, the dryer outlet has a separate ground wire as well as the two hots and a white. I seem to remember having to change the cord on the dryer when I got it , I knew nothing about the 3 vs 4 wire, but I do not understand why the old trailer would have 4 prong outlets, not that I mind, will make things easier but i don't get it, is it just a matter of the breaker rather than the main service wire?
     
  2. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    All residential services are 3 wires from the utility, L1, L2 and N. All new 120V/240V dryer/stove circuits are 4 physical wires, L1, L2, N, G. So all 120V/240V dryers/stoves installed on new circuits should use NEMA 14 type plugs with 4 wires, and any bonding strap within the appliance connecting L-N must be removed. [Some new European appliances are 240V only, and so the circuit would be 3 wire L1, L2, G, and the plug would be NEMA type 6.]

    In the past, it was allowed to run a 3 wire 120V/240V dryer stove/circuit that was just L1, L2, and N, with no G. In that case you have a NEMA 10 type plug with just 3 wires, and you must install the bonding strap in the appliance to bond the case to N, rather than leave it floating. Existing 3 wire 120V/240V circuits may continue to be used like this under an NEC exception; certain future possible modifications to an electrical may require upgrading those circuits to 4 wire circuits.

    So the upshot is that 3 wire vs 4 wire has to do with the age of the circuit wiring from the panel to the appliance receptacle.

    Cheers, Wayne
     
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  4. James23912

    James23912 Member

    Joined:
    May 16, 2020
    Location:
    Vermont
    Um, so I don't quite get what you mean, the receptacles are all the same? So I still need to change the appliance cord? The new house wiring to the outlet seems to be exactly the same as that in the trailer, I assumed it would be different and the older outlets would also look different, like 3 prong in the trailer vs 4 prong in the new house? Basically what I am trying to figure is if I need to change the cords on the appliances, I have seen diagrams where you do something like cut the tab that the white wire was on and then add the new ground to the cut off section? That is what you mean by the bonding strap? I was figuring the older stuff did not have a ground so I was surprised to see one, I read that the white wire used to serve as ground, sorry to be so dense. I have not looked inside the appliance themselves, just the outlets, which I thought would be different in the old vs the new . the new ones I bought look the same as the old ones.

    I have to leave for work, will check the appliances tomorrow, thanks
     
  5. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    If the receptacles are the same (4 prong, aka NEMA 14 series) and correctly wired, and if the appliance plug matches, and if the appliance cords are correctly wired with the bonding strap removed, then all you have to do is plug them in.

    If you have a multimeter it's easy to check the unplugged appliance to see if the bonding strap has been properly removed. Just check for continuity between the neutral prong on the plug and the ground prong on the plug--there shouldn't be any. If you want to check that the ground wire in the cord is properly terminated inside the wiring compartment, check for continuity between the ground pin on the plug and an exposed unpainted metal part of the chassis-you should have continuity.

    Cheers, Wayne
     
  6. kevink1955

    kevink1955 Member

    Joined:
    Nov 17, 2011
    Location:
    L.I. New York
    I think what James was getting at in the original post was that he had a 3 wire service to the trailer, I am assuming the trailer was feed off a power pole remote from the trailer. That would make the power pole the main disconnect, anything after the disconnect (the trailer)should have been 4 wire although there may have been an exception many years ago.

    Now to make things confusing, the house that he is calling 4 wire actually gets 3 wires from the utility co. The 4th wire is a ground bar that has the ground rod, water service and a jumper to the utility neutral.

    Todays code requires the dryer to have 4 wires 2 hot, 1 neutral and 1 ground. Even though the ground is connected to the neutral (bonded) at the main service panel it is required to be run as a separate wire.

    Since by todays code the neutral to ground bond should only happen once (at the service panel) just make sure any jumpers installed in the appliance have been removed and go with your 4 wire cord and receptacle.

    Just go with 4 wire all the way and assume the 4 wire outlets in the trailer were wired incorrectly or had jumpers installed that should not have been there.

    Improper grounding (bonding) can make the cabinet of the appliance live in relation to other grounded objects around it and can kill.
     
  7. James23912

    James23912 Member

    Joined:
    May 16, 2020
    Location:
    Vermont
    Hi thanks for the responses, I should have looked at the appliances beforehand, I had it in my head that the older outside wire meant the inside things had to comply with that, but once again I was wrong. I took off the dryer cover and, after removing the poor mouse that had gotten fried in there, saw that there is indeed a separate neutral so I can go with the existing power cord and return the one I bought, I am assuming the stove is the same and will check later. This is the problem with only doing something once, you learn the correct way but never have to do it again. I really appreciate the help, this place is great
     
  8. mikha'el

    mikha'el Member

    Joined:
    Jan 27, 2015
    Location:
    Texas
    Amazing how mice can find their way into a connection box, only to short themselves into mummification.
    Found a small lizard the other day in my outdoor load center that had done the same - just a skeleton.

    As mentioned - your building ground is established at the service disconnect, the incoming service is 3-wire no ground.
     
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Ground should never have any current on it...it is there for safety. Neutral is bonded to ground at the panel entrance, but neutral is really the return for 120vac circuits...you need a complete circuit for power to flow.

    Older 240vacv appliances sold may not have had a safety ground. But, because current DOES flow through the neutral when 120vac is used (if your stove has an oven light, it is very probably a 120vac bulb, and if any display or receptacles on it, normally, 120vac as well, so neutral is required).

    So, having a safety ground makes things safer, but on stoves, dryers, they grandfather the power connection, so if you do have a 3-wire connection, you can still use it, but must make the proper connections inside of the device.
     
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