I'll try to keep this short but there is a bit of background info that may be needed. Couple of days I rented a floor grinder to eliminate uneven concrete floor in the basement. The grinder kept tripping the breaker every 10 or so minutes. All the circuit breakers in the main panel are 10 amp. Needles to say I took the equipment back and was told that this kind of equipment requires a minimum of 15 or 20 amp circuits.

Quite disappointed not being able to finish the project I started thinking and I realized that recently I added a new sets of duplex GFI outlets (one GFI and 3 regular) in the garage using a #12 wire but only a 10 amp breaker to match the rest. Can I replace the 10 amp breaker for a 20 amp? I mean the 12 gauge wire should be OK, I just wondered why the builder chose 10 amp breakers in this house.

  • Also, 10A breakers? That's mighty strange for the USA... – ThreePhaseEel Jan 7 '17 at 23:17

The short answer is that the breaker protects the wire (otherwise, heat and fire can result). You can put a 20A breaker on a circuit if all the wire on the circuit is #12. If any of the wire is #14 you can put a 15A breaker on it. If any of the wire in the circuit is smaller than #14, then you cannot put a 15A breaker on it.

  • Thanks, I thought that was the case. All the wire is #12. – Risho May 26 '15 at 2:20
  • 5
    +1 But that means ALL the wire, including the wires to any light fixture, not just the wire to the outlet you are using for the grinder. – bib May 26 '15 at 2:48
  • Yep, all the way to the fixture itself (smaller wires inside of fixtures and devices don't count). – Craig May 26 '15 at 5:01
  • Also make sure the outlets are rated for that amperage. – Brian from state farm May 26 '15 at 12:50

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