rule of thumb -- watts for 3 ton AC

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  #1  
Old 03-26-11, 09:35 PM
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rule of thumb -- watts for 3 ton AC

Hi:

I'm looking for a guesstimate or rule of thumb to give me an idea of how much current is drawn by a 3-ton 220V central AC unit (outside compressor and condenser).

Eventually I want to install a 3 ton unit, and am wondering if a 40A 220V circuit will be sufficient.

I can't seem to find any manufacturer on the web who will divulge this info without getting involved with a dealer.

Thanks,
s/Mike
 
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Old 03-27-11, 07:04 AM
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Correct voltage for the calculation would be 240v not 220v.
 
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Old 03-27-11, 07:39 AM
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They are rated per unit, so it will depend on the manufacturer. What is so difficult in getting a contractor involved? Just asking the question because I've seen many 3 ton units all with different size breakers needed. It also depends on the efficiency rating of the a/c. Best to get a contractor involved. The breaker also has to be HACR!
 
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Old 03-27-11, 11:59 AM
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rule of thumb -- watts for 3 ton AC

If you want to run the wire now, why don't you just leave the breaker
out for now until you get your unit. If you ran a #10 wire than you are covered for up to 30 amps, and the never run more than that, but you can always put a smaller breaker in. paul
 
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Old 03-28-11, 12:54 PM
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I am a homeowner, with a 3 ton 11 year old unit, and I'll tell you straight up what my outside unit pulls. The compressor pulls about 11-12A, and the fan pulls about 1-2A. That totals about 14A (max steadystate, not including surge) @ 240v. But I can tell you that the circuit is protected by a 50A breaker both at the garage box, as well as the outside disconnect.

I had an AC tech over recently, and he made a comment that a 50A breaker was a bit higher than necessary. Since the house was built in 1974, I assume AC was less efficient back then and subsequently pulled more power, but I don't know for sure the exact reasoning for my 50A breakers.

I bet if I replaced one or both of the breakers it with a 30A breaker, that would more than cover the circuit, assuming the high startup surge of the compressor wouldn't trip it. I may do this myself just for kicks and grins.
 
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Old 03-28-11, 04:26 PM
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This topic got me thinking. On the way home I purchased a 20A breaker and replaced the 50A breaker for the outdoor unit with this one. I put the 20A breaker in at the main panel in the garage, and left the larger breaker outside next to the unit. The outside unit started fine and so I am going to keep this configuration unless the 20A breaker starts tripping under normal use. It is definitely safer this way.
 
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Old 03-28-11, 04:48 PM
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ensure your new breaker is HACR. Also, instead of just putting a breaker you think will work in (even though you are probably correct about the size) check the data plate on the A/C for a recommended breaker or a max fuse.
 
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Old 03-29-11, 08:10 PM
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thanks for responses

Howdy:

Sure do appreciate the responses that have come forth.

The main reason I am asking is I had a 40A breaker in a 4-T (maybe only 3 1/2T) unit back in the early 70's. I was thinking that a 40A circuit would be more than enough for a modern 3T unit; however, one vendor (who will remain anonymous) says that I will need a 60A breaker for a 3T 14 SEER unit--and I find that to be ridiculous.

What say, you experts ...
 
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Old 03-29-11, 08:12 PM
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I highly, highly doubt it.................
 
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Old 03-29-11, 09:06 PM
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rule of thumb -- watts for 3 ton AC

Originally Posted by billybard View Post
Howdy:

Sure do appreciate the responses that have come forth.

The main reason I am asking is I had a 40A breaker in a 4-T (maybe only 3 1/2T) unit back in the early 70's. I was thinking that a 40A circuit would be more than enough for a modern 3T unit; however, one vendor (who will remain anonymous) says that I will need a 60A breaker for a 3T 14 SEER unit--and I find that to be ridiculous.

What say, you experts ...
The old 10 seer were usually 30 amp breakers and the new higher eff are less amp than the old ones.
 
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Old 03-29-11, 11:12 PM
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You could need a 60 ampere circuit breaker for the inside (air handler) unit. Less than 15 amperes for the blower itself and the rest for the back-up electrical heating elements.
 
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Old 04-18-11, 07:05 AM
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Update: I've been running on a 20A breaker on my 3 ton outside unit for the last few weeks and it is working perfectly.
 
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Old 04-18-11, 07:45 PM
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whatever size you need, just make sure you get hvac breakers and size your wire correctly.
 
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Old 04-19-11, 05:14 PM
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All the info you will need is on the nameplate:
Minimum circuit ampacity
Maximum fuse or circuit breaker.

Nameplate in for should be had from the manufacture of the unit is not physically there.
 
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