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I have a 2 part question.

  1. Can you connect an existing 4 gauge wire to a 15 amp breaker? (The wire is already there, instead of me pulling everything out.)

  2. Can I connect this 4 gauge wire to a 14/2 cable and run it underground to a GFCI outlet on the fence post?

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  • You can try and after three hours of trying you will find just using the right size wire is faster. Will find that 4 gauge will not fit into a 15 amp breaker well.
    – crip659
    May 17 '21 at 19:21
  • If fence post is a good distance away from breaker, might try 12 gauge, if using outlet for ~12 to 15 amp tools/motors.
    – crip659
    May 17 '21 at 19:31
  • The problem is the 4 guage wire is really hard to pull out from the conduit. I have tried. That was my first choice. Can I also merrete the wire at the breaker box to 14/2 that way it will fit 15 amp breaker?
    – William
    May 17 '21 at 20:49
  • That is what @isherwood suggested. Run 14 or 12 gauge from breaker to junction box and connect 4g to it. Need junction box for the splice to be code.
    – crip659
    May 17 '21 at 21:11
  • #4 awg won't fit in a 20A breaker either, but it's probably worth the cost to use 12/2 and use a 20A breaker and give yourself a little more capacity. (You can put a 15A duplex on a 20A breaker.) May 18 '21 at 3:55
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Yes you can put 4 awg wire on 15 amp breaker.

However with this size wire you will find nothing fits a #4 directly so you will need to get a splice.

splices that actually connect wires as large as 4 awg to wires as small as 14 awg the part number is 971022 Morris. I just happen to have a dozen on my desk. you can find them for ~6$ ea . Depending on how far away the receptacle is this could be both a big savings and no voltage drop issues. Or just easier than pulling a new line but it is totally code compliant to do this.

There are other brands of these connectors / splices like Polaris I just happen to have the exact model you need on my desk (they are very handy).

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  • Yes, you're always allowed to use larger wire than is required. Only proviso is pigtailing terminals that won't take the fat wire, and increasing ground size in proportion with conductor size. May 18 '21 at 21:20

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