Oven neutral or not

Discussion in 'Electrical Forum discussion & Blog' started by Sleepless, Jul 3, 2014.

  1. Sleepless

    Sleepless New Member

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    I will soon be remodeling our kitchen. The present wall oven location will be moved about 10' across the room. The present 8/3 wire (40 amp circuit) runs in the ceiling. The ceiling sheet rock will have to be removed anyway so I planned to just pull the existing wire to the new location (resulting in a shorter run).

    The problem is that we are going from a 1978 3-wire oven to a 4-wire (convection) oven (why can't they use 220 fans and transformers!!!). (The new oven will only need a 30 amp circuit.) The installation information from the manufacturer allows for a 3-wire installation "where codes permit" -- see attached file. I had a discussion with the salesman at the (large) appliance store, he talked in a very large circle, but implied that an existing 3-wire circuit would be acceptable, but a "new" installation would require a neutral.

    I certainly want to comply with code, but running a new wire in an existing house will be a real pain.

    Do I need to run a new 4-wire circuit to the new location?

    Attached Files:

    Last edited: Jul 3, 2014
  2. PatrickH

    PatrickH New Member

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    Location:
    Virginia
    The exception to this is applicable to existing installations with no grounding conductor in the box. :(
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
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    This is my understanding...if you are putting a new stove/oven in the same place, and it is wired with three wires, you can install the new one IF the appliance allows it. Otherwise, you must run a new cable with 2-hots, neutral, and separate ground. The old unit probably does have some 120vac stuff in it, and internally tied the neutral and ground point together. That is not allowed in a new install...the ground and neutral must be separate. All new units internally have neutral and ground separated, but if being installed on a three-wire circuit, they tie the ground and neutral back together. It is safer to have an independent ground wire to trip the breaker if there's a fault.
  4. Sleepless

    Sleepless New Member

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    Yes indeed, the existing oven has a timer and light bulb that are 120vac. I haven't pulled out the old unit, but since there is no neutral from the panel, it must have its ground and neutral joined.

    The question is -- would this be classified as a new install or a replacement.
  5. hj

    hj Moderator & Master Plumber Staff Member

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    quote; I haven't pulled out the old unit, but since there is no neutral from the panel, it must have its ground and neutral joined.

    You are mistaken. It DOES have a neutral, but it does NOT have a dedicated ground.
    Speedy Petey likes this.
  6. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

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    Location:
    NY State, USA
    Just to clarify. Older "3-wire" 120/240V range and dryer circuits ALWAYS required a neutral. It was the ground that was allowed to be omitted. The neutral served both purposes.
  7. Sleepless

    Sleepless New Member

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    I do understand that the neutral and ground are shared, or one can say that the case ground is not dedicated.

    The question is more practical, does moving the oven location require a new 4-wire circuit?

    (I still don't understand why these are built as 120/240, they could easily be built as 240. Certainly any appliance exported to Europe is not going to be 120/240!)
    Last edited: Jul 4, 2014
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
    New England
    Generally, moving things requires it to be brought up to current codes...a direct replacement may not. Best directed to your local inspector.
  9. hj

    hj Moderator & Master Plumber Staff Member

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    quoe; Certainly any appliance exported to Europe is not going to be 120/240!)

    And WHY would it be, since they do not have 120 v power. A customer from the "old country" put out all his Christmas decorations and could not understand why they were all "yellow", until I told him they were for 220 but were running on 120 and he would need to buy new decorations.
  10. Reach4

    Reach4 Active Member

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    Sleepless's point was why would a US oven that did not have an AC outlet on it even use a neutral? I think the answer would have been because 240 volt oven light bulbs would be hard for a US customer to get. I wonder if they will figure out how to use LEDs for ovens. Not for a while, I expect due to the temperatures.
  11. PatrickH

    PatrickH New Member

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    Location:
    Virginia
    We don't distribute power the same as European Countries. In Europe 230 volts is from the conductor to ground (i.e. Neutral), as where here in the states, it's usually 240 volts between the two conductors, and 120 volts to ground. It really doesn't matter though. Appliance companies likely don't create, at least in large numbers, appliances that can operate in either grid. You could take it up with the local inspector if you aren't able to pull a new feed for the range. Or you could tell us where the panel is, if you need some tips on running a new range circuit to it.
    Jadnasua is right that adding the dedicated ground will yield a safer installation for you and the family. Connecting the neutral and ground at the appliance means that the case will be part of the circuit. If the grounded leg is severed or loose and you or someone else provides a better path to ground via the sink faucet etc, then you could get a shock from the case of the range. GL.
  12. hj

    hj Moderator & Master Plumber Staff Member

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    Location:
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    I may be wrong, but I have heard that some countries, like Australia, only have a single 240v wire coming in to the building. The "neutral" is taken care of by an "earth/ground" connection.
  13. Reach4

    Reach4 Active Member

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    Location:
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    If you were worried enough about a shock with the shared neutral, you could put in a 30 Amp 2 Pole Ground Fault Circuit Breaker into the breaker panel to replace the breaker you have now.
  14. Sleepless

    Sleepless New Member

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    Interesting -- how does the GFCI know there is an imbalance between the two poles and ground if the common and ground are connected at the oven?
  15. Reach4

    Reach4 Active Member

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    huge2.png
    The worry would be if there was a current between the stove and something else. The GFI runs the three conductors through a small sensing transformer that only looks for the algebraic sum of the 3 currents (ideally zero). http://www.schneider-electric.us/support/index?page=content&country=US&lang=en&id=FA115047
    http://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf page 11.
    Last edited: Jul 7, 2014
  16. Sleepless

    Sleepless New Member

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    This oven has two fans (110VAC) -- is a motor load on a GFI circuit a potential problem?
  17. Reach4

    Reach4 Active Member

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    Location:
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    No.

    What could trip the breaker is if the neutral is connected to the oven frame, AND also some external ground or source connects to that frame and that connection passes over 4 milliamps of current. Now there is a path of current in addition to the 3 wires going through the differential current transformer.
    Last edited: Jul 7, 2014
  18. Sleepless

    Sleepless New Member

    Messages:
    10
    But that is the recommendation of the manufacturer (for three wire connection), neutral is connected to the oven cabinet via the green wire (see illustration in first post).

    I will have other grounds available in the area (cooktop and dedicated circuit for microwave above oven).
  19. Reach4

    Reach4 Active Member

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    Location:
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    I edited my previous post to turn the first two sentences into a single sentence. It would take both things to trip the GFI breaker.

    If the wire that would have connected to the green in a 4-wire setup is connected to nothing rather than the white neutral, then touching the oven frame with an outside ground would not trip the GFI. If the wire that would have connected to the green in a 4-wire setup plus the oven neutral is connected to the white neutral in your cable, then touching the oven frame with an outside ground or other connection might trip the GFI. It would depend how much current flowed.

    In regular convenience outlets, it is not required that the chassis/protective ground be connected if there is a suitable GFI. I don't know what the rules would be according to code. I think I know what I would do. I would not connect the chassis to ground. I would let the terminal that would have gone to the green float. However don't do it because I would do it. I am not a electrician. I tend to look at circuits from an electronics point of view and not a NEC code point of view.
  20. Sleepless

    Sleepless New Member

    Messages:
    10
    Seems like it would be preferable to pull a ground from the microwave circuit for the oven case ground. (Bare wire in 3-wire 120/240vac "R0mex" connects to oven neutral only)

    Not sure this would jive with the NEC!!

    I do understand how the GFI would protect IF the case is not connected to the neutral.
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