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I'm new here, so I'll apologize in advance! But I successfully wired up my garage with the helpful information from electricians on job sites and LOTS of research on forums! I had to remove the 20amp breaker that fed 1 outside receptacle at the house from the main service box in order to fit the 100amp breaker feeding the sub panel in the shop. I had enough extra 10-2 direct burial to run from the new sub panel at the shop back to the receptacle at the house so I threw it in the ditch and backfilled it! It is about 150 feet one way.

My main questions/ concerns- 1- Given the distance, could I run the 10awg the first 130 or so feet and then use 12awg in a junction box closer to the receptacle to feed the receptacle for fitment issues?

2- I have an LED flood light on a switch with 12-2 direct burial that I'd like to run on the same circuit. Yay or nay?

3- I won't be using much from the receptacle at the house and the LED flood light won't use much current, so I feel like I'm good with the 20 amp circuit, or should I put it on a 15 amp breaker to be safe?

4- What is the best way to splice at a junction box, wire nuts or the screw down type connectors?

Thank you in advance for your help and sorry if I was unclear about anything (A.D.D. is working overtime today! Hahah!)

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  • Breaker must match the smallest wire size in the circuit. When the next person working in the panel sees 10# wire they will ass u me that a larger breaker can be put on this circuit.
    – Kris
    May 29, 2021 at 18:03
  • Yes, I understand the breaker size for wire size. As for people down the line, I will probably make a note on the panel as to the wire size down the line to avoid confusion (or attempt to avoid it!) Thank you for giving me that idea!
    – David Hazel
    May 29, 2021 at 19:38
  • I was mainly concerned with the length of the run and voltage drop being that I'm going 150 feet. Does the breaker size have to compensate for the length of wire? Example- 12awg is good for 20 amps, but will a 200ft. run of 12awg on a 20 amp circuit burn the wire before tripping the breaker? The outlet and flood light were on a 15 amp circuit before I had to remove it because there was 14awg wire running to the receptacle, which will be removed and replaced with 12awg on a completely different circuit and I never tripped the 15 amp breaker.
    – David Hazel
    May 29, 2021 at 19:53
  • How much load are you actually planning to put on the circuit?
    – ThreePhaseEel
    May 29, 2021 at 19:56
  • 1
    Use @ThreePhaseEel to alert that user to your comment.
    – Kris
    May 29, 2021 at 21:48

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You'll be fine here

With your pressure-washer load on a 130' run of 10AWG copper, you're a bit over 3% voltage drop, and the LEDs will draw next to nothing atop that. So, I wouldn't worry too hard about your plans. What you make the splices in your "junction box" with depends on if you're dealing with an aboveground box or an underground handhole, though. For the former, you can use standard wirenuts or lever-lock type connectors; however, for the latter, you'll want to use connectors rated for direct burial, as handholes get quite wet inside.

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  • Thank you very much for your help! You've eased my over-thinking mind! But just for my own curiosities sake, is there ever a time when a wire size will become too hot due to length of the run to cause a failure in the wire itself before tripping the appropriate sized breaker or is it just a matter of severe voltage drop? Ie- 700 feet of #12 on a 20 amp breaker would melt the wire before the breaker trips or you'd just have 70ish volts at the receiving end?
    – David Hazel
    May 30, 2021 at 1:44
  • @DavidHazel -- its just a matter of voltage drop
    – ThreePhaseEel
    May 30, 2021 at 1:58

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