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Old 11-07-2007, 06:31 AM   #1
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Wiring an A/C Unit


Power will be coming straight from my panel, correct me if I'm wrong, but I believe it needs its own 30amp breaker. Question: I've got 10/3 w/g here from the previous window A/C plug, can I use i for 30amps to the new unit? I'm pulling the old plug and filling the hole, I was thinking of reusing this wire and re-routing it to the disconnect of the new unit.

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Old 11-07-2007, 08:53 AM   #2
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Wiring an A/C Unit


Is this outside central air at a condensing unit for a split system or another window a/c??

You mention disconnect so sounds like outside condenser/compressor or heat pump for central air/heating.

Yes you probably can use the 10/3 G you need to get the minimum ampacity and max. breaker size off the name plate then we can tell you what you need.

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Old 11-07-2007, 10:19 AM   #3
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Wiring an A/C Unit


Outside central air. They're coming later this week to install it new. Previously we used window units so without needing those anymore I'm pulling the wires and filling the outlet holes. Haven't seen the unit yet so I can't tell you the name plate numbers. Just thinking I could reuse the 10/3 to avoid buying another $80 worth of wire.
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Old 11-07-2007, 10:34 AM   #4
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Wiring an A/C Unit


Make sure it is just an AC unit and not a heat pump. Heat pumps have a compressor, condenser fan motor and possibly heat strips. If it's a heat pump you are going to possibly need three circuits. One for the condensing unit outside, one for the evaporator unit located inside and one for the heat strips.
I would let the HVAC people install the electrical. They know the unit and what requirements need to be followed.

Note: The condensing unit outside and the evaporator unit inside could be on the same circuit. Thus two circuits.
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Old 11-07-2007, 02:16 PM   #5
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Wiring an A/C Unit


Well you have the cart before the horse. Regardless you will have one 240 circuit to the outside unit and a thermostat control circuit. If you have a gas furnace then you will have an "a-coil" installed for the cooling of the air via the furnace blower motor. The outside unit will have a compressor and fan motor whether A/c condensor or heat pump. Most all A/C split systems are 10 guage wire or less in most moderate square footage homes. So I venture to say you will be fine with 10/3 G only you will not need the neutral white wire as the circuit will be 240 volt. So it just gets capped. You will need an outside disconnect close to the A/C. You also need a 120 volt maintenance outlet within 25 feet for service technicians. I would get an a/c disconnect like one of these if you don't have a 120 volt receptacle within the correct distance.




You will need to run a seperate 15 or 20 amp circuit to the 120 volt outlet The upper black box is the A/C pull out disconnect. Get a 60 amp rated one. Nice way to go.

Do you know what the HVAC guys are going to be responsible for? Very possible they will not do the hard wiring.

They going to hook to the disconnect or are you?

Do you know the unit size and make? We can probably get the specs online.
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Old 11-14-2007, 09:47 AM   #6
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Wiring an A/C Unit


http://www.goodmanmfg.com/Portals/0/pdf/SS-GSC13.pdf

Page 3 is the specs, they put in a 2 ton so product code is GSC13024. They installed everything but the electrical (wanted $300 to run a wire 20' through my crawl space) so I'll be doing that. If I'm reading correctly it says max. draw is 20amps, so why the 60amp disconnect recommendation Stubbie? Also, he says they normally install the units with 12/2 WG and use black and white both for hot, then run the ground to the unit's ground. I looked in the panel, sure enough the unit needs 2 hots and a ground. But I can't mix recommendations, 12 wire to a 60amp breaker just won't happen. What are your thoughts?

By the way..... I'm in Michigan so I don't have to wire this thing up anytime soon!
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Old 11-14-2007, 11:14 AM   #7
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Wiring an A/C Unit


It is not a 60 amp breaker, it is a 60 amp rated switch. It proivides no protection for the unit, just a place to turn the power of so it can be serviced.
The 10/3 will work if it is long enough, jsut don't connect the white wire to anything. connect the black and red wire to the breaker in the panel and connect the ground wire to the ground terminal. Put a wire nut on the white.
The max breaker you can use is a 20 amp, so you need to replace the breaker in the panel.
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Old 11-14-2007, 12:51 PM   #8
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Wiring an A/C Unit


I can't add much to what JBfan just posted, I am in agreement with him. The 60 amp AC disconnect can be just that... a disconnect... and does not require a breaker if you put a 20 amp double pole common trip in in the panel to protect the wire. Even if you had a 60 amp breaker in the disconnect the 20 amp would trip way before the 60 could cause any problems...it would simply be a expensive disconnect. You only need the non-breaker/fusible type. These usually have just a pull out block to denergize the circuit. Look this over to get an idea what we are talking about....you will notice that almost all a/c disconnects that are non-fusible are 60 amps this is the industry standard and covers all reasonable installations for residential applications. Smaller a/c disconnects like 30 amps are usually the fusible type....you don't need this.

http://www.midwestelectric.com/catal...MEPB-DIS06.pdf

The requirement for the disconnect size is a calculation that incorporates the Locked rotor amps of the compressor unit, looks like yours is 54 amps locked rotor condition. The end result of this calculation determines the disconnect size. 60 amp disconnects pretty much cover most residential disconnect requirements.
We are talking about the required maintenance disconnect not a breaker protecting the branch circuit conductors. This image shows the required 120 volt service receptacle, the A/C disconnect is on the side of the house by the condensing unit.

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Old 03-07-2008, 10:40 AM   #9
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Wiring an A/C Unit


Bringing this back up because I'm curious where I can find a disconnect with a receptical like in Stubbie's picture? The only one I can find is at Midwest Electric for $135! Any idea why so pricy? If that's the case I'll put a $15 disconnect next to a $20 GFCI outlet!

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