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Thread: Subpanel Circuit Question

  1. #1
    DIY Junior Member mln's Avatar
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    Default Subpanel Circuit Question

    I have a 4-circuit subpanel with twist-in type fuses branching off a 40-amp breaker in the main house panel.

    A living room circuit that I'm working has 6 duplex receptacles. As I was pigtailing some wire to the old flex armored BX cable I noticed that the original wire gauge seemed heavy. I looked at the fuse that I had removed and it's rated for 30-amps. The old receptacles that I took out were standard 15-amp.

    My question is, does it make sense to replace the fuse with a 15-amp fuse then safely pigtail with 14-gauge wire using standard duplex receptacles??

    Part two of the question is this... there is another 30-amp fuse in the subpanel used for a bathroom circuit. The other two circuits have 20-amp fuses - they're used for misc. lighting. Does it sound like all of these fuses are over-rated? Should I just replace all with 15-amp fuses??

    Thanks for any guidance.

  2. #2
    In the Trades Bob NH's Avatar
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    You should compare the diameter of the copper conductor with a conductor of a known size. It may be #12. I doubt that someone would run #10 to receptacle branch circuits. If it is smaller than #12 it is probably #14.

    Fuses should be not larger than the following sizes:
    15 Amp for #14; 20 Amp for #12; and 30 Amp for #10 wire.

    You should also check at the subpanel to verify that the fuse is correct for the wire size going from the subpanel. That is the place that I would start.

  3. #3
    DIY Junior Member mln's Avatar
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    Thanks for the reply. I'm estimating the existing wire to be #12. Erring on the side of caution do you see any trouble with using a 15 amp fuse. As I mentioned, it's a living room so there will be a few lights and a tv, laptops will be plugged in, not much else.

  4. #4
    In the Trades Bob NH's Avatar
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    There is no problem with a 15 Amp fuse on wire that is at least #15.

  5. #5
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by mln
    Should I just replace all with 15-amp fuses??
    When we had to have a new breaker panel installed not long after we got this 1920s house, I had the electrician use only 15-amp breakers on all the circuits even if they had heavier wire ... and over two years later, I still ended up with one circuit shorting somewhere and tripping a breaker while waking us up with a bright flash at about 2AM.

    I know next to nothing about types of wire, but I do not trust the old stuff.
    Last edited by leejosepho; 09-19-2007 at 07:53 PM.

  6. #6

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    With multiple receptacles on the circuit as long as the feeding wires are 12 gage then you can use a 20 amp fuse. If there pigtailed off the main line with 14 gage this is still fine. If the power passes through the receptacles (in at the bottom and out at the top) then you need to use 15 amp fuse.

    This is the same for your other circuits.

    I’m assuming this is copper wire that’s in good shape.
    I will say that I do not trust old wire, old breaker, and fuses.

    ***edit***
    I bet someone was popping the fuse so they put in a 30 amp fuse. What all do you have on this circuit?
    Last edited by got_nailed; 09-20-2007 at 05:49 AM.

  7. #7
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by got_nailed
    With multiple receptacles on the circuit as long as the feeding wires are 12 gage then you can use a 20 amp fuse. If there pigtailed off the main line with 14 gage this is still fine. If the power passes through the receptacles (in at the bottom and out at the top) then you need to use 15 amp fuse.
    HUH?????

    If there is ANY #14 on the circuit you MUST use a 15A breaker. Pigtails DO count.
    Any receptacle is capable of carrying 20 amps. With #12, even if you are using the receptacle to feed through the circuit you can still use a 20A breaker.

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