4 Wire Cooktop and Oven to 3 Wire Sub Panel

Discussion in 'Electrical Forum discussion & Blog' started by TJanak, Dec 28, 2011.

  1. TJanak

    TJanak Member

    Messages:
    155
    Location:
    South TX
    I have a sub panel that runs all household circuits other than HVAC. It is three wire, i.e. all neutrals and grounds bonded in subpanel. (not ideal, I know).

    I am installing a new electric cooktop and oven and need to purchase wire. These are 4 wire appliances. Do I get 2+G wire or 3+G wire? The old range had 2+G wire with bare ground. Seems to me the bare ground would not be cool.

    The manufacturer lists both 3 and 4 wire connections.



    Btw, the cooktop calls for a 50 amp circuit. 8 or 6 awg?
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Do they cord and plug or are they hard wired?

    Copper or aluminum

    If connecting cooking appliances to a three wire the conductors must land in the service not in the remote panel
  3. TJanak

    TJanak Member

    Messages:
    155
    Location:
    South TX
    Hard wired and copper.

    I can connect them to a four wire that runs to the sub panel :D

    Seriously though, are my options to run dedicated circuits for the cooktop and oven 90' to the service entrance or get a whole new sub panel and run new 2-3G from the service to the sub?

    I understand the reason for neutral and ground to only be bonded in the service entrance but neither of the two options I see are very practical.
  4. Chad Schloss

    Chad Schloss Member

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    here is a thread you asked the same stuff in from 2009.

    http://www.terrylove.com/forums/archive/index.php/t-33514.html
  5. Chad Schloss

    Chad Schloss Member

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    jw, what do you do in his situation (in his old thread i posted) where he has his main breaker outside and the panel inside is now considered the sub panel? would this not be allowed?

    copy of the post

    "For what it's worth, yesterday I looked at my parents house which was built in 1988 or so. It is set up exactly like my house except my meter and main panel are on the house. They have one main panel on the meter pole and the sub in the house is wired the exact same way mine is, even including the dryer."
  6. TJanak

    TJanak Member

    Messages:
    155
    Location:
    South TX
    Chad, I know I had that old post from 2009 but I wanted JW's opinion.

    Besides, I didn't really come to a conclusion from that post because of this:

    Exception: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units,clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be connected to the grounded circuit conductor if all the following conditions are met.

    (1) The supply circuit is 120/240-volt, single-phase,3-wire: or 208y/120-volt derived from a 3-phase,4-wire, wye-connected system.

    (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 or a Type SE service-entrance cable and the branch circuit originates at the service equipment.

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

    At the time I should have pressed the issue more but the other advice I got at the time was to leave it alone so that is what I did.
    Number 3 above reads to me like it's ok if I use an insulated grounded conductor to my existing sub panel. Or would be considered ok if the existing circuit was wired in this way.
    Last edited: Dec 28, 2011
  7. DonL

    DonL Jack of all trades Master of one

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    3 + G Copper, 8 AWG 75Deg.C Minimum. / or 6 AWG 60Deg.C
    Last edited: Dec 29, 2011
  8. jwelectric

    jwelectric Electrical Contractor/Instructor

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    I highlighted in red the part of the exception that counts. We can't just pick one of them we must comply with ALL of rhwm
  9. jwelectric

    jwelectric Electrical Contractor/Instructor

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    If the SE cable is installed in insulation or NM is used then we can't use 75 degree so the #8 would be to small
  10. TJanak

    TJanak Member

    Messages:
    155
    Location:
    South TX
    All of the conditions are currently met except for (3) The grounded conductor is insulated...

    I appreciate the help JW.
  11. jwelectric

    jwelectric Electrical Contractor/Instructor

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  12. TJanak

    TJanak Member

    Messages:
    155
    Location:
    South TX
    It's not a receptacle but hard wired. I don't see how that makes a difference. Does it?

    Ok, help me understand this:

    Should the equipment grounding conductor be reconnect to the neutral downstream from the service equipment then from the point of the second connection back to the service all equipment grounding conductors are at the same potential as the circuit supplying them.

    From my point of second connection (sub panel) back to the service is a 3 wire #2 NM type cable. 3rd wire not insulated. I understand this 3rd wire would be carrying current.
    Does this mean all grounding conductors after the point of second connection are at potential as well?
  13. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Yes but I would almost bet that the subpanel is fed from the service equipment.
    It is not unusual for a code official to allow the three conductor feeder to remain when a service upgrade takes place so as not to pose an undue hardship on the homeowner. What happens is an official with no electrical background will allow this to take place with a three wire dryer or range is fed from the panel which is a big NO! NO!

    I would never install a three wire cord on either a dryer or range if there was any way to not do so.
    When a three wire set up on a dryer or range is installed the frame of the appliance is connected to the neutral conductor. This neutral is a current carrying conductor so what does it make any metal connected to it?
  14. TJanak

    TJanak Member

    Messages:
    155
    Location:
    South TX
    Gotcha.

    So basically the code allows 3 wire for existing installations but all new work must be 4 wire with neutral and ground bonded only at service entrance.
  15. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Location:
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    This is correct

    EDITED TO ADD;

    I should have said that a three wire to a remote panel is never code compliant but it is sometimes allowed under special circumstances.

    Three wire dryer and range circuits are sometime allowed under special circumstances.

    But if it was not code compliant when it was installed it is not code compliant just because it is existing.

    Due to oversight, lack of knowledge, or whatever the reason should a service upgrade be made and the existing SE cable (three wire) be allowed to remain to the remote panel then the code has always required the dryer and range to be upgraded to a 4 wire circuit.

    Moving the dryer or range to the new service equipment means that it is no longer existing but has been moved which will require them to be installed using a 4 conductor cable or 4 conductors if installed in a raceway.
    .
    Last edited: Dec 30, 2011
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