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I'm installing a 240V/30A ductless mini-split. I have a disconnect with 120 V GFCI outlet. The wiring from the panel is 10 ga.

Can I can wire the receptacle from that same HVAC branch circuit (with neutral), assuming I use 10 ga between the disconnect line side lugs and the outlet? Or do I need a separate 120 V branch circuit?

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There is no need for a 120V circuit to be part of a mini-split installation.

People often get confused by this because of a clause in Code. That is there to address the needs of the A/C maintainer to plug in their vacuum pump or test equipment. This is satisfied by ordinary, existing outdoor receptacles and their circuits that houses have normally to power garden tools, BBQ stations, Christmas lights and the like.

There is no need for a special 120V circuit just for the A/C repairperson's benefit (that would be silly).

All Code is saying is that outlet must be within 25' of the mini-split outdoor unit. No big deal.

If you don't have such an outlet already, think about which location would be most convenient for your other household uses that is within 25' of the outdoor unit. And then just tap a bedroom circuit or whatever is on the other side of the wall there.

As long as it's not a circuit dedicated to receptacles in bathrooms, laundry, kitchen or garage, which are special. (NFPA's reason for the garage dedicated outlet circuit is for EV charging - thanks NFPA. However if the circuit could be flipped to 240V/20A, that charges at 4KW or 100-120 miles per 10-hour night session, which is all 95% of people will need.)

You cannot put a 15/20A GFCI on a 30A circuit

This is forbidden by NEC 210.21. So merely hanging a receptacle off that disconnect is not a viable plan.

The outlet needs to be protected by a 15A or 20A circuit to match the socket size (if there is only 1 socket).

Therefore you would need to delete the disconnect and replace it with a full and proper subpanel containing a 30? amp breaker for the heat pump and a 15 or 20 amp breaker for the 120V circuit. The subpanel will need the standard 30" wide x 36" deep working space around the subpanel that is level and kept clear at all times.

One might argue there's no need for a wire size enlargement on the feeder, because the outlet will only be used when the heat pump is switched off. However an inspector would argue that it is actually a general-purpose receptacle usable for BBQing or plugging in electric lawnmowers, and its ampacity needs to be accounted for.

But there's another problem with the subpanel approach. Larger motors have their overcurrent protection onboard the motor. Because of that, the supply breaker can be enlarged above normal sizes to prevent nuisance trips. However, once you move that breaker to the subpanel, the breaker in the main panel loses that benefit, and the larger breaker necessitates larger wire. This is getting costly.

The best answer is to find an existing outdoor outlet within 25', or extend any old 120V circuit to provide one.

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  • Thank you for that clarification. I was aware that I only needed an outlet within 25', but had none, hence the desire to use the integrated outlet. Would be nice if the manufacturers made disconnect boxes with a 15/20A breaker in them just for this purpose. I do have a bedroom branch circuit I think I can tap. There's a window right above the installation location with an outlet beneath it, I don't suppose that meets the 25' requirement? ;)
    – Rick
    Sep 21, 2022 at 0:18
  • @Rick yeah, I don't think so lol. Sep 21, 2022 at 2:29

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