Which circuit for my garage A/C?

puttster

Hi everyone, this is my first post. Hope it works out!

I have a new detached two car garage with two 115v 15A circuits in it. I want to put in a 12000 BTU window air conditioner. One circuit runs 10 fluoresent bulbs in the garage and a few in the house but also runs a few outlets in the house that see occasional use by a 12A vacuum cleaner. The other is solely used for the door opener and outlets in the garage where I often use a 12 amp skill saw.

Both circuits are aqccessible, which one should I choose?

Puttster

AandPDan

How many amps is the air conditioner? 120 volt, you're probably talking 9-10 amps at minimum.

The air conditioner should really be on it's own circuit. As it cycles on/off it will draw more to start.

I'd be looking to upgrade the service to the garage.

puttster

A/C is 12 amp.

AandPDan

OK. Neither.

You say you have two circuits from the house panel. There is NO panel in the garage?

You don't have the ampacity to run a saw and the a/c. You'll be juggling cords. The same happens if someone runs the vacuum and you have the a/c on that circuit.

Time up upgrade your garage feed.

I ask about what you have now because, depending where you live, you can only run a single or a multi wire branch circuit to your garage. NEC 225.30. If not a MWBC, you can't have the two circuits that you do.

I'd suggest putting in a small subpanel sized depending upon what you figure your loads will be. Then a dedicated circuit for the a/c. If you check the directions it probably recommends that it be installed on it's own 20 amp circuit.

J. V.

Two circuits to the detached structure are a code violation. Do away with one or both and or a small sub panel. There is plenty advice on this site concerning the sub panel installation. Use the search function.

puttster

Interesting, this is a brand new house in Houston, TX. Maybe they live by a different code?

puttster

Actually I was dismayed at the box where the wires from the house were wirenutted to the wires from the garage. It was packed! Three 14/2 and a 14/3.

Looks like one wire on one circuit goes to the garage door & outlets. The other three are for the lights and are on the other breaker. I think the reason for so many wires is the outside lights, one on the house and one on the garage, controlled by one switch in the house and one switch in the garage. I tried to draw it out but got baffled.

puttster

a7ecorsair

Maybe it is a MWBC and the OP is seeing two breakers in his panel for this. Still not enough for the A/C though.

k_buz

Are you SURE there are two breakers that control the garage?

I can account for the cables you mention without a second circuit.

14-2 power in
14-2 power out (to recepts)
14-2 switch leg (to lights)
14-3 3 way to house

puttster

Of the four cables entering the garage, one goes to the garage outlets. The breaker labeled "Garage GFI" controls this. The other three, conttolled by "Hall lights & rec" drop down the wall to two switches there.

One switch controls the outside lights. The other switch controls the inside lights. They are right beside each other. So maybe the electrician figured, "Why make another run to get power to the inside light switch when I have some right here?"

puttster

[quote=puttster;911026]Of the four cables entering the garage, one goes to the garage outlets. The breaker labeled "Garage GFI" controls this. The other three, conttolled by "Hall lights & rec" drop down the wall to two switches there.

One switch controls the outside lights. The other switch controls the inside lights. They are right beside each other. So maybe the electrician figured, "Why make another run to get power to the inside light switch when I have some right here?"

Whatever the cause, still looking for a recommendation. I'm leaning toward using the lights circuit and just put childproof plugs in the affected house outlets... like anybody uses a vacuum cleaner at our house anyways! Maybe at the A/C put both circuits in one receptacle and if one kicks out, use the other one - let the best man win!

AandPDan

Recommendation:

Put in a proper subpanel and feeder in the garage. Then put in some circuits to handle your expected load with a DEDICATED CIRCUIT for the air conditioner.

k_buz

What you are proposing to do is what we call "a homeowner special". It might work, but its illegal. Shoot, the garage wiring to start with is against code. All electric in the garage must be able to be disconnected in the garage. If there are lights on the garage that are switched in the house, the power for the lights must come from the garage. To make it simple, there must be a "main" disconnect for all electric in or on the garage in or on the garage.

Your AC pulls 12A and you only have 15A to start with, its not going to take much to trip the circuit. If you put on the door opener circuit, you won't be able to use the opener (much less the skill saw) and the AC. If you put it on the other circuit, you won't be able to use the lights (standard 2 lamp ballasts are usually just uner 1A) and the AC.

puttster

I opened my main service box with the idea of adding a 220 to the detached garage. There are six or seven places left for adding circuit breakers. What is tough to see is how I will get the new wire into the box. Looks like all the existing circuits exit through one two inch hole that leads into the house wall. How do you get a new circuit into the box?
puttster

Jim Port

There should be pre-punched knockouts for new cables in the panel. You will need to use a connector.

Sounds like the existing cables do not meet the code. There are several requirements to leave the panel through a sleeve and not through individual connectors.

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Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.