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10/2 air conditioner wiring - clarification

53K views 45 replies 14 participants last post by  beenthere 
#1 ·
Hello All,

I have a licenced electrician coming in the house to install a new Central Air Unit. The material are currently in my garage and I see he's using 10/2 wire and a double pole breaker.

I "know" both wires in the 10/2 are hot/lead wires, but conceptually I can't wrap my head around it.....is there no neutral?
 
#4 ·
10/2 is acceptable for a single-appliance circuit where the appliance needs ONLY 220v. Central air compressors would usually fall in this category.

You'd need 3 wire cable (with a neutral) for appliances where an appliance may require dual voltages. Examples might be a range, where 110 is used for the lights/timer/clock/etc and 220 is used for the heating element; another would be a clothes dryer where the tumbler motor runs on 110 but the heater runs on 220.

3 wire cable is also used for subpanel installation, e.g. to a garage, because your subpanel needs a neutral.

In short, a neutral is needed in any situation where the destination might need 110 for any reason. For your AC unit, there shouldn't be a reason for it to need 110v, so feeding the 220v circuit without a neutral works fine. Remember, voltage across the two hots is 220v, and voltage from either hot to neutral is 110v, this is how we can have dual voltages.

(Note that when I say 3 wire cable, I mean 3 wire + ground. Same for 2-wire cable - 10/2 cable should contain two 10 gauge hots plus a ground. You NEED a ground on any new installation, I don't believe there are are any common exceptions to that.)

As suggested before, just make sure all other codes are complied with. You need a GFCI outlet, but AFAIK it can run off a separate circuit (in my house the GFCI outdoor outlet by the AC unit runs off my furnace's circuit while the AC has a dedicated circuit.) Also make sure you follow any codes for cable that goes outdoors (if I recall right, it needs to be armored and/or in conduit)

F
 
#5 ·
10/2 is acceptable for a single-appliance circuit where the appliance needs ONLY 220v. Central air compressors would usually fall in this category.
I'm not sure what you mean by "a single-appliance circuit". 10/2 can be used for ANY straight 240V circuit 30A or less.




Also make sure you follow any codes for cable that goes outdoors (if I recall right, it needs to be armored and/or in conduit)
No such code like that that I know of.
 
#8 ·
Neither armored cable or conduit is required outside by the NEC.

Bringing the NM into the back of the disconnect should be fine. NM cannot be used from the disconnect to the unit.
 
#11 ·
I did noticed the OP is from Canada the rules should be simauir to the NEC is.

But for sure I know Joed is from Canada and he can reply this question related to the CEC codes.

Merci,
Marc
 
#21 ·
busman said:
Not if it doesn't say THWN.

Mark
And how often do you see straight THHN? Almost never.
 
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#25 ·
I've only been on this forum for a few weeks. I came to get reasonable answers/ideas from reasonable people. However, this forum seems more of a school yard mentality (my dad's better than your dad).

Anyone know a forum where I don't have to filter though all this bs?
 
#26 ·
Might I suggest you get a thicker skin or possibly be less picky?
I don't know what thread you are reading but in this one all I see is adult discussions about technical issues.
Can you point out the "my dad's better than your dad" stuff you are talking about?
 
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#32 ·
Location, Damp. Locations protected from weather and not subject to saturation with water or other liquids but subject to moderate degrees of moisture. Examples of such locations include partially protected locations under canopies, marquees, roofed open porches, and like locations, and interior locations subject to moderate degrees of moisture, such as some basements, some barns, and some cold-storage warehouses.

Location, Dry. A location not normally subject to dampness or wetness. A location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction.

Location, Wet. Installations under ground or in concrete slabs or masonry in direct contact with the earth; in locations subject to saturation with water or other liquids, such as vehicle washing areas; and in unprotected locations exposed to weather.
 
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