I'm a complete newbie to this so I have a few questions...

1) Gauge of wire from panel to exterior subpanel? I know it's two live from a 220V breaker and neutral, also do I need GFCI, or a standard breaker is fine, 30amps good?

2) Conduit, hard or flex, and composition of conduit? I would prefer hard, also any restrictions on height when running on exterior of house, obstacles of windows & Main line in the way, how to avoid? Can I push away from the wall with a treated two by four or do I have to route away?

3) Do I need a subpanel outside? Does it need to be fused? Any distance / placement requirements to ground level, windows, ac condenser unit, ac pressured lines?

Thank you for taking the time to respond to my questions.


https://senville.com/18000-btu-dual-zone-mini-split-air-conditioner-sena-18hf-d/ this is the unit I was looking at installing, looks to be 18A with Max Fuse at 25A.

Yes, the exterior subpanel is on the same physical building on a different side of the house feeding from behind the house.

I'm located in Toronto, Ontario, Canada.

  • Power requirements of air conditioner? (Amps and/or Watts) Commented Jun 11, 2020 at 17:32
  • Is this exterior subpanel on the same building as the panel its feeding? Commented Jun 11, 2020 at 17:32
  • Can you tell us where you are? Most will assume US, but you know what happens... Even within the US, different states/municipalities have adopted different versions of the NEC and have made their own exceptions to the rules.
    – FreeMan
    Commented Jun 11, 2020 at 17:48
  • Hi I updated the posting answering everybody's questions. Commented Jun 11, 2020 at 20:16
  • Is there a reason you want/need a subpanel at the air conditioner location, instead of a simple disconnect switch? Commented Jun 11, 2020 at 20:36

1 Answer 1


12 gauge wire is sufficient up to 20 amps. 240v (except for stove and dryer) needs 2 conductors and a ground (no neutral), so 12/2 should do it. The black and white will be the two legs, then the ground.

You must have a disconnect at the unit. Run your line from the breaker box to the disconnect. If the line is inside an attic or wall or under the house it is considered “protected”. I ran mine under the house,stapled to the underside of the floor joists. At the disconnectI drilled a hole through the outer floor joists the outside. I drilled the hole large enough to accommodate 1/ inch rigid conduit through the hole to the outside, and rigid conduit up to the disconnect. I haven’t gotten past this point, but some sort of whip will run from the disconnect to the unit.

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