1

My house has a 10 gauge wire leading to a 50 amp breaker. My understanding is this is not allowed and the conversation should end there.

However, this circuit is for the AC unit which specifies a minimum circuit amps of 33 amp and a maximum breaker of 50 amp. HVAC folks are telling me the 10 gauge wire is fine in this case. Why is it acceptable to seemingly violate the normal code specifically for an AC unit?

  • Is your AC outdoor unit hooked up using a NM or UF cable, some type of metal-sheathed cable, or wires in conduit? – ThreePhaseEel Feb 21 '17 at 0:56
2

Because it IS NOT "violating the normal code". It is following the codes allowed for A/C units.

Electrical codes are not nearly as black and white as home centers and quick code guides will lead you to believe.

NEC 240.4(D) restricts smaller conductors (14,12&10) to lower than what is in the general ampacity charts. It also says this applies unless allowed in 240.4(E) & (G). 240.4(G) says 240.4(D) does not apply to certain installations, A/C units being in that list. Depending on the conductor and application #10cu might be rated for 30, 35 or even 40A.

If this is a bit confusing I can post all the relevant articles.

  • Thanks for the thorough answer. Does the code differ for A/C units because they are incapable of continuously drawing the higher current rating, but they still could benefit from a larger breaker due to potential spiking on startup? – TTT Feb 21 '17 at 5:31
  • Yes, that is one of the main reasons. Also, most have some kind of internal protection, like motors that have thermal overloads. – Speedy Petey Feb 21 '17 at 12:40
  • I'll note that you would most likely be breaking code if at some later date you decided to snitch power from this feed by tying into the existing #10 run. – Carl Witthoft Feb 21 '17 at 18:02
  • @CarlWitthoft, what would you possibly snitch power for from a dedicated A/C circuit??? – Speedy Petey Feb 21 '17 at 18:46
  • 1
    @SpeedyPetey you have no idea what some "creative" homeowners will decide to do. :-( – Carl Witthoft Feb 21 '17 at 21:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.