AC Wiring size for 2 ton Unit

6 years ago

last modified: 6 years ago

Inlaws are having a central AC unit attached to their 10 yr old furnace. Small house - about 1200 sq ft. Two contractors bid the job - both would rather I run the wiring as the basement is finished and they dont want to pull ceiling tiles (which is fine since I did it all years ago and know the routine). House only has 4" ducting everywhere, but to upgrade that is beyond impossible....both budget and without tearing alot of other things out. House is very well insulated. One contractor wanted to install a 1.5 ton unit. Said to run 10ga wire with a dual 30A circuit. Contractor two wants to install a 2 ton unit and said to run 12ga with a dual 20A circuit. I know code allows 12/20, but I'm indifferent - to run one is as good as the other and I dont mind erring on the side of overkill.

Which sounds more correct?

Thanks in advance.

Featured Answer

sktn77a

6 years ago

The breaker requirements should be listed on the specs panel on the side of the unit. The contractors' suggestions seem backward - are you sure you didn't get them reversed?

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Comments (13)

weedmeister
6 years ago
Does 'dual circuit' mean 240v?
handyguy7 thanked weedmeister
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Living in NoVA, I can tell you that those electric rates are too low. I have Dominion which should be the same as yourself. The rates are broken up into two parts: Distribution and Supply. Supply is also broken down further. They also vary for winter/summer. To see the exact rates, you would need to look at the tariff. Off of my April bill, ignoring taxes and credits, $90.96 / 769 kwH = $0.118/kwh. Yes, there is a step rate above 800kwH but I think it lowers slightly. 11 cents would be fine for a cost estimate. Oh, and I paid something around $7k for a 2.5ton single stage Trane system a few years ago. Fair amount of labor removing the old indoor system, running new electrical and refrigerant lines, etc.
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handyguy7
Original Author
6 years ago
last modified: 6 years ago
sktn77a - Nope....thats exactly the instructions they each gave and is written on the estimate. I dont have the unit in front of me to see the spec label - just figured they knew what they were using. Both are 30+ yr HVAC installers to boot.

weedmeister - double pole.
handyguy7
Original Author
6 years ago
There is already a 12ga line run to the area (was a dedicated plug for a window AC they used for the last few years), and I think that will work fine. Just was wanting a second opinion if I was to re-run a 10ga line instead. Probably not necessary, but that doesn't mean it wouldn't be a better idea.
klem1
6 years ago
You need to use breaker recommended on unit tag. Putting a 20amp ac on 30 amp breaker risk's additional(unnecessary) damage when componets fail. Using 10 guage wire is ok for 20 or 30 amp breaker. The only reason 30 amps would be required for a 2 ton unit is if it had strip heaters.
handyguy7 thanked klem1
PRO
Austin Air Companie
6 years ago
last modified: 6 years ago
It's very rare that HVAC contractors are licensed electricians. While our control wiring knowledge is 'typically' second to none, we are not licensed to run wire (except thermostat wire). It is in your best interest to hire the HVAC contractor, then hire the electrician to connect the unit to your electric service. Unless the HVAC has written in the contract that he will hire and supervise the electrician and include that in the job.

Why it's important: for the simple reason you risk a fire. If the wire is not sized properly it will be come a load. The longer the AC runs, the hotter that wire gets, until a fire starts.

The breaker merely trips when it's amp rating has surpassed the rating of breaker or there is a direct short to ground or a furious trip would be if the two pole wires made contact. That in some cases may blow the main and in further cases may do even more damage than that.

Air Conditioners should be placed on their own circuit, If attached to an A/H with strip heat the A/H with strip heat should have separate breakers.
handyguy7 thanked Austin Air Companie
mike_home
6 years ago
Two HVAC contractors who have 30+ years experience want the homeowner to install the electrical wiring! It appears they have no intention to apply for permits.

There is nothing wrong with removing the drop ceiling panels in order to save time and minimize the risk of damage. However the HVAC contractor needs to hire a licensed electrician and apply for a permit. This is especially true when he demonstrates little knowledge of the electric code.

Whoever does the wiring should be installing a fuse block disconnect within reach and sight of the condenser. This is a requirement of the NEC (National Electric Code).
handyguy7 thanked mike_home
handyguy7
Original Author
6 years ago
last modified: 6 years ago
The basement is low - 7ft maybe - and with pipes they are a tight fit, so I get it if they're afraid of damaging them. I would rather do it than to have that happen anyways. There is a disconnect 2 ft from the condenser and its all on its own double pole breaker. 12ga will work and is to code, so thats probably what will be used. I'm surprised a contractor (let alone 2) actually showed up. Impossible to get any contractor (for any job) to show up, call, etc. Whether either one of these actually show when its time, or even bother to call when they aren't, is another story. I wont hold my breath. House needs sided too and thus far 4 have been no-shows/no calls.
PRO
Austin Air Companie
6 years ago
There are many variances in wire sizing requirements, such as length of run, the load being placed upon it and so on.

Many places a disconnect with in sight of the condenser (for residential application) is all that is needed to satisfy code.

Problem many have in knowing what should be versus over kill is due to the confusion from commercial and industrial requirements to that of residential.
handyguy7 thanked Austin Air Companie
handyguy7
Original Author
6 years ago
I forgot to mention that the run is only about 30-35 ft.
weedmeister
6 years ago
Chances are the unit requires a 30 amp circuit. So use the 10 gauge.

FYI: mine is a 2.5 ton, replaced a 2 ton using the same circuit. 8 gauge and 30 amp breaker.
handyguy7 thanked weedmeister
handyguy7
Original Author
6 years ago
Thats what I was kind of thinking to begin with. Thanks.
sktn77a
5 years ago
last modified: 5 years ago
Wiring shouldn't be a problem if its correctly sized or oversized. Just don't undersize it. However, please be sure to use the breaker size specified on the unit. It's there for a reason. Too small and you will have nuisance trips. Too large and you risk damaging the equipment with surges and shorts.