A/C Condensor Wiring Question.

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StreamlineGT

StreamlineGT

Senior Member
I have heard from many, that even though it is not common practice with electricians, to wire condensor loads with a small wire, big breaker.

Here's the specs.

min. circuit ampacity - 19a
min breaker size - 25a
max breaker size - 30a

Now I have been told that I can run a 12awg NM to this on a 30 amp breaker. Am I confused? Would it be better to run a 12awg on a 25? Should I just run a 10awg on a 30 and call it a day?

It just seems like it defies logic, but for some reason I remember learning this in class.... a long time ago.
 
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You are allowed to run 14 AWG to this and use a 30 amp breaker.

Then minimum circuit ampacity is 19 amps, 14 AWG is rated 20 amps.

It is safe and compliant, although for voltage drop reasons I would probably use 12 AWG if this run has some length to it.
 
OK, so let me ask you this, and only because I have a wake to goto, and I can't do the calc, so someone please help me.

2 units like above. 90 feet of conduit. running both circuits in one conduit. 12 awg good for derate and voltage drop? all 240v.

Thanks a million!
 
I can't do the calcs right now but I will add the conductor protection is in the unit, that is why it is OK. Breaker protects against short circuits and ground faults the motor overloads protect the conductors from long duration overload.

BTW, to actually due VD calcs you need the running load amps not the MCA.
 
StreamlineGT said:
OK, so let me ask you this, and only because I have a wake to goto, and I can't do the calc, so someone please help me.

2 units like above. 90 feet of conduit. running both circuits in one conduit. 12 awg good for derate and voltage drop? all 240v.

Thanks a million!
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Voltage drop is fine with #12 using the VD calculator here
 
The reason i always ran larger (usually #10 romex) is just for my own safety . Never can be sure what the AC guy will set. If it turns out to be heat pump with aux heat strip you could be in trouble. Just simply cover yourself.
 
Jim W in Tampa said:
The reason i always ran larger (usually #10 romex) is just for my own safety . Never can be sure what the AC guy will set. If it turns out to be heat pump with aux heat strip you could be in trouble. Just simply cover yourself.
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I tend to use nothing smaller than #10 also but for different reasons. #10 is not all that expensive so if an addition is added and they need a little more umphh in the cooling then the wire is there. Interestingly, as units have gotten more efficient you can now use a larger unit with a high seer and it draws less then the old er units.
 
Not sure about up north but here in FL many want heat pumps cause more efficient to heat in winter. Problem is they often have 5 kw heat strip. Now if i am doing track homes and they spec straight cool 2 1/2 ton 13 seer then sure use #12 but be sure the GC understands he can't change the unit on you.
 
Jim W in Tampa said:
Not sure about up north but here in FL many want heat pumps cause more efficient to heat in winter. Problem is they often have 5 kw heat strip. Now if i am doing track homes and they spec straight cool 2 1/2 ton 13 seer then sure use #12 but be sure the GC understands he can't change the unit on you.
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Unless I am missing something here I thought heat strips always went in the air handler, not the condensing unit.
 
vinster888 said:
if you standardize what you install you can save money that on bulk purchases. so id be pulling #10 with a 30A OCD
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You don't have plenty of 12 and 14 on the job, too? :-? You're not a one-size-fits-all kinda wireman, are you?

I make it clear that I need hard data on all major appliances and HVAC gear on all jobs before starting it.
 
LarryFine said:
You don't have plenty of 12 and 14 on the job, too? :-? You're not a one-size-fits-all kinda wireman, are you?

I make it clear that I need hard data on all major appliances and HVAC gear on all jobs before starting it.
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You been lucky if you got all that. I was never sure what might show up. Last thing you ever want is to be cutting up walls to change wire size even if it was the GC at fault.
I would hope you have plenty of #14 and #12 already on the job.
 
Jim, why not just run an empty raceway like ENT or PVC to the disconnect location if you get into trouble that often? A coil of ENT seems like cheap insurance.
 
peter d said:
Jim, why not just run an empty raceway like ENT or PVC to the disconnect location if you get into trouble that often? A coil of ENT seems like cheap insurance.
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If you get into trouble that often it might be time to smack somebody. ;)

Get the specs, run what is required, done. If They screw you on what they end up installing screw them back.
 
its not often but is costly. I prefer to run #10 and be over kill. And for now not doing houses. On commercial just emt till unit set. Even had them change voltage and not tell anyone
 
Jim W in Tampa said:
its not often but is costly. I prefer to run #10 and be over kill. And for now not doing houses. On commercial just emt till unit set. Even had them change voltage and not tell anyone
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that and order equipment without asking about voltages...
220, 221 !! "it just plugs in anyway"
 
StreamlineGT said:
OK, so let me ask you this, and only because I have a wake to goto, and I can't do the calc, so someone please help me.

2 units like above. 90 feet of conduit. running both circuits in one conduit. 12 awg good for derate and voltage drop? all 240v.

Thanks a million!
Click to expand...

I thought you mentioned NM in the OP???
 
iwire said:
You are allowed to run 14 AWG to this and use a 30 amp breaker.

Then minimum circuit ampacity is 19 amps, 14 AWG is rated 20 amps.

It is safe and compliant, although for voltage drop reasons I would probably use 12 AWG if this run has some length to it.
Click to expand...

Bob, did you use the 60 degree C column to get the amp rating of #14 romex or the 75 degree C column? I was taught to use the 75 degree C column for motors and disregard wire type. not sure of what code reference that comes from though.
 
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