Subpanel neutral/ground isolation

Discussion in 'Electrical Forum discussion & Blog' started by Homeownerinburb, Jan 14, 2012.

  1. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    I purchased a house a while back that has three, yes, three panels. The original panel has ten circuits and a 40 amp master. It feeds most of the house. It is fed by a 100 amp panel that has breakers for the cook top and the wall oven, plus four 20 amp 120 v circuits. This was rendered a sub panel when central air was installed along with a 200 amp panel.

    I saw that the sub panels did not have their ground connections to the panel up stream segregated from the neutral, so I went about installing lugs or small buss bars for the grounds to tie them to the panels while keeping the neutrals separate.

    But I was having trouble. On the first panel described, one of the neutrals to a three wire circuit read as tied to the ground somehow, even after I had disconnected it from the buss bar and it was connected to nothing else.

    The neutral seems to be tied to the ground somewhere down stream. How am I to find that?

    And in the middle panel, the neutrals for the cook top and the oven seem to be likewise continuous to the ground, when tested similarly.

    Possibly I am using the multi-meter poorly? I am just using the continuity setting with the audible alert. Should I be setting the meter for a particular resistance?
  2. cacher_chick

    cacher_chick Test, Don't Guess!

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    Location:
    Land of Cheese
    Most older appliances like ranges and driers have the neutral and ground bonded in the appliance connection. When the appliance is connected to a circuit with a separate neutral and ground, the bond in the appliance must be removed.

    If there is neutral and ground available at a cord and plug appliance, the receptacle and cord should be of the 4-wire variety.
  3. kreemoweet

    kreemoweet New Member

    Messages:
    371
    Location:
    Seattle. WA
    You're going to have to check all the connections on the offending circuit, if you can find them. Neutrals could be
    connected to neutrals from other circuits, which are in turn connected to ground in the main panel.
  4. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    Have been looking. Can't seem to find it.
  5. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
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    Location:
    North Carolina
    From the panel that has the service disconnect (the breaker that turns everything off) are the remote panels wired with 4 wire cables?
  6. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    Three wires in conduit.
  7. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    See, this is what confuses me. For decades, apparently, houses with a single panel and large electrical loads like a stove and a dryer had the ground and neutral bonded in more than one place.

    Were people being fried all across the nation?
  8. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Is the neutral in each panel insulated and isolated from the panel enclosure
  9. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    Yes, that was the obvious measure. I disconnected everything from the two buss bars and tested for continuity to the enclosures. None there. I then tested each white wire for continuity to the enclosure while it was loose. As I wrote at the top, one of the neutrals for a three wire circuit on the 10 circuit panel showed continuity to the enclosure. But I don't know what sort of resistance the path sees.

    And at the middle panel I found both white wires from the cook top and the wall oven were continuous to the enclosure.

    I installed lugs or a small buss bar directly to the enclosure to tie in the grounding wires.

    Oh, I wrote that there were three wires and conduit. That was the third panel to the second panel. From the newest panel to the second panel there is conduit and four wires, one green. Fixed now to the main buss at the main panel and to a grounding buss at the second panel.
  10. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Then if the conduit is metal that would be the equipment grounding for the feeders it would mean that there is a neutral/ground bond in the cooking appliances. If they are fed with three insulated conductors in metal conduit or a four wire cable the bond needs to be removed at the appliance
  11. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    I'll look for it.

    Now, why would it be OK for there to be a bond even if the appliance were fed from the main panel?
  12. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Only in one case is the frame of a cooking appliance or dryer to be bonded to the neutral. It must be an existing installation that originates in the service equipment.
  13. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA

    The bond is not going to be in the socket, but in the appliance?
  14. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,248
    Location:
    Land of Cheese
    The bond will normally be found where the cord terminates in the appliance.

    The grounding lug on the proper 4-wire receptacle must be bonded to/in the receptacle's box with the correct threaded screw.
    Last edited: Jan 15, 2012
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