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Residential Wiring - The Right Way!

Wiring Information for the Do It Yourself Homeowner

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Thread: Sub Panel

  1. #1
    Join Date
    May 2015
    Posts
    2

    Default Sub Panel

    I have a 1950s home 1/2 of the home is 2 wire with no ground the other 1/2 of the house has been remodeled and has grounded outlets
    When the remodel was done they installed a 200 amp service panel. The original service panel is run through the new panel on 100 amp breaker.
    I ran into I trouble today because I installed a Nano Salt Water Fish tank and felt I should have a GFI at the outlet that would be used for the tank. It was a grounded outlet so I ASSumed that it was on a breaker in the main service panel. None of the breakers killed the power, so I went to the Sub Panel- none of those breakers killed the power. I finally turned the 100 amp breaker to the sub panel and that terminated power to that outlet.
    When I took the existing outlet out there was 12/2 Romex with a ground. So I installed the gfi outlet. After I returned power and tested the outlet it tripped when I pushed the button and reset as it should. I then checked it with one of the cheap 3 light gfi testers it would not trip but says reverse/neutral reverse.
    I checked and the black wire is hot and in the appropriate side, the white wire was not energized and also on the appropriate side but the ground wire was hot?

  2. #2
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    215

    Default

    Sounds like there are some issues there. If the ground is truly hot, you need to be careful when doing the following tests. First a question -- what were you using to determine if a wire was hot or not? Many testers and meters can read a "phantom voltage" on wires that aren't connected.

    Next, are you sure that circuit has no breaker (other than the 100A one feeding the sub panel)? I would look into the main panel and see if there is a set of #12 wires in that 100A breaker along with the larger wires that go to the sub panel. If there are no smaller ones, I don't know how that circuit could be live unless it is on feed through lugs or the main lugs in the subpanel. Again, look in the subpanel for a set of #12 wires mixed in with some fatter wires on a live lug with no breaker.

    Power on the grounding wire will confuse a lot of testers. It is possible you have something that is faulted and putting power on the ground wire, but that ground isn't terminated back at the panel so it isn't tripping the breaker. This is quite dangerous. It could also be phantom voltage. If there is enough power on the ground to run a 15W light bulb, it is dangerous. Having a 15W test lamp connected between neutral and ground would help determine if this is true 120V or phantom voltage (if it light up brightly, then it is really live and can shock you). If true 120V, I would turn breakers off one at a time until that hot ground goes dead. The circuit you turn off will have the failed item, so try to unplug or disconnect everything from that circuit and turn the breaker back on. Did the ground go live again or stay dead? If dead, plug the items in one at a time until the ground becomes hot and that's the failed item.

    Your GFCI is probably working correctly if its test button is making it trip. But a hot ground defeats the purpose and the GFCI doesn't care about the grounding wire. An external tester requires a working ground wire to trip a GFCI. I'm pretty sure that ground wire doesn't have a path back to the panel so it is no good. That return path needs to be fixed and running a single green or bare #12 wire from any ground on that circuit back to the panel ground bar would accomplish that.
    Last edited by suemarkp; 05-06-2015 at 10:20 PM.
    Mark
    Kent, WA

  3. #3
    Join Date
    May 2015
    Posts
    2

    Default sub panel

    Thanks for your quick response.
    I found the culprit of the hot ground wire
    The previous owner had pig tailed a piece of romex just outside of the JB and out of sight. He or she had tied the ground to the hot wire.

    Sub Panel problem
    The sub panel has 6- 15 amp breakers - then below that 2- 30 amp breaker that are NOT tied together and then 2 sets of 30 amp breakers that ARE tied together. I was unable to terminate power to the outlet because you have to turn off one of the 15 amp breaker and also one of the 30 amp breakers. Not understanding what they were doing.

    I am going to start checking all of the outlets that are on these circuits and see if there is a problem in any of them. After that I will resort to the attic and see if I can find anything there. The only blessing of older homes is that everything is in the attic or under the house in the crawl space. Got to love pier and beam.

  4. #4
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    215

    Default

    Sounds like two circuits got tied together somehow. 30A single pole breakers are rare in dwellings, and you usually only see them for RV outlets. A 30A double pole would be common for a water heater or clothes dryer. Track down those 30A single poles as they are not allowed to feed hardly anything except a 30A 120V power receptacle. And they need to have #10 wire on them. You may need to replace them with 15's or 20's depending on what is connected to them and the size wire used.

    Oh, and if they did tie 2 circuits together into a ring, there's a 50-50 chance it will work. If the breakers are on opposite phases, they will both trip as there is a 240V short circuit. If they are on the same phase, both must be turned off to kill power to the circuit and you won't be getting hardly any overload protection as the load current will divide between both breakers (e.g. a 25A load would be pulling 12.5A through the 20A breaker and 12.5A through the 30A breaker, so they will never trip).
    Last edited by suemarkp; 05-07-2015 at 02:47 PM.
    Mark
    Kent, WA

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