Electrical Mismatch

[Jim Katen]

If you look at the first photo posted, the manufacturer states no bigger than a 25 amp breaker. or fuse Just above that is a line that says the minimum ampacity is 14.4. This means you can use a 25 amp breaker with #14 awg because #14 can be used with up to 15 amps. The stated ampacity is what determines the wire size, not the breaker. As far as I know (and I stand ready to be corrected) it may be the only exception to the NEC rules, and it's ok with the NEC. If you can't find a 25 amp breaker, a lot of installers put 25 amp cartridge fuses in the exterior disconnect box. Yes, you can use #12 awg or #10 awg with this as you can always have a larger than required conductor but it is more than what is required. Of course, I agree with you, using larger than required is good, at least in wiring. Also, yes, I think experience means a heck of a lot, but just because someone has done something the same way for 20 years doesn't make it right. And I just went to Home Depot, on the shelf were a GE, a Square D, and an Eaton 25 amp two pole breaker, highest price was 16.80. (http://www.homedepot.com/webapp/wcs/sto ... c=1&Ntpr=1) If you need one, I'll buy it and ship it to you for a small surcharge.

If I saw a 14AWG wire in a circuit using a 25 amp breaker, I'd call it out. Sure, the unit might be ok with a 14AWG feeder but in that case I would want to see a 15 amp breaker protecting it. The unit label says 25 amp breaker max. That doesn't mean it's ok to to over fuse a 14AWG with a 25 amp breaker. I too stand ready to be corrected if needed.

If you put a 15-amp breaker on it, the breaker would probably trip every time the compressor started up.

14 AWG wire must be protected against overcurrent, short circuit fault current, and ground fault current. In the case of an air conditioning compressor circuit, the circuit breaker is only there to provide protection against faults and to provide a way to cut power to the circuit. The overcurrent protection is built into the compressor motor. It's perfectly acceptable to have a 25-amp breaker with #14 wire in this case.

[Marc]

If you look at the first photo posted, the manufacturer states no bigger than a 25 amp breaker. or fuse Just above that is a line that says the minimum ampacity is 14.4. This means you can use a 25 amp breaker with #14 awg because #14 can be used with up to 15 amps. The stated ampacity is what determines the wire size, not the breaker. As far as I know (and I stand ready to be corrected) it may be the only exception to the NEC rules, and it's ok with the NEC. If you can't find a 25 amp breaker, a lot of installers put 25 amp cartridge fuses in the exterior disconnect box. Yes, you can use #12 awg or #10 awg with this as you can always have a larger than required conductor but it is more than what is required. Of course, I agree with you, using larger than required is good, at least in wiring. Also, yes, I think experience means a heck of a lot, but just because someone has done something the same way for 20 years doesn't make it right. And I just went to Home Depot, on the shelf were a GE, a Square D, and an Eaton 25 amp two pole breaker, highest price was 16.80. (http://www.homedepot.com/webapp/wcs/sto ... c=1&Ntpr=1) If you need one, I'll buy it and ship it to you for a small surcharge.

If I saw a 14AWG wire in a circuit using a 25 amp breaker, I'd call it out. Sure, the unit might be ok with a 14AWG feeder but in that case I would want to see a 15 amp breaker protecting it. The unit label says 25 amp breaker max. That doesn't mean it's ok to to over fuse a 14AWG with a 25 amp breaker. I too stand ready to be corrected if needed.

If you put a 15-amp breaker on it, the breaker would probably trip every time the compressor started up.

14 AWG wire must be protected against overcurrent, short circuit fault current, and ground fault current. In the case of an air conditioning compressor circuit, the circuit breaker is only there to provide protection against faults and to provide a way to cut power to the circuit. The overcurrent protection is built into the compressor motor. It's perfectly acceptable to have a 25-amp breaker with #14 wire in this case.

Agreed. The initial amp draw of a compressor motor is approximately the same as the locked rotor amps, usually about 2 to 3 times the full load current. That's for single phase, capacitor start motors. For 3 phase, it's a factor of about 6 times the full load current.

Marc

[John Dirks Jr]

Is over current protection always built into the the compressor motor to a rate that complies with the service label?

If so, I stand corrected and further educated. If not, then what?

[Marc]

Is over current protection always built into the the compressor motor to a rate that complies with the service label?

If so, I stand corrected and further educated. If not, then what?

The presence of a manufacturer data plate specifying minimum ampacity and maximum OC protection implies that the compressor motor within has the built in protection, IMHO, since the electrical characteristics of that protection are among the factors in the calculation of the min ampacity and max OC values.

Marc

[John Dirks Jr]

I've don't remember seeing anything other than #10 for AC feed. If I would have run into a #12 on a 30amp I would have written it up. I guess I won't do that now.

It's nice being corrected before making the mistake. I guess forum participation is helpful in that respect sometimes.

Charlie, I shouldn't have second guessed you but I'm glad I did anyway.

[John Kogel]

I've don't remember seeing anything other than #10 for AC feed. If I would have run into a #12 on a 30amp I would have written it up. I guess I won't do that now.

It's nice being corrected before making the mistake. I guess forum participation is helpful in that respect sometimes.

Charlie, I shouldn't have second guessed you but I'm glad I did anyway.

I'm inclined to agree with you, John. Minimum ampacity may be 14.4 amps, but what is the max? As Marc says, maybe 2 or 3 times that at every startup. If the compressor seizes up, the breaker won't trip until the current reaches 25 amps or more. Running a #14 gauge feeder inside a wall and feeding it with a 25 amp breaker would be asking for trouble, IMO.

Simply put, the label does not say to use a #14 supply cable. Does it? [?]

Interestingly, the Canadian (CEC) rule, here for static heating loads, such as electric baseboard heating, allows us to use a wire gauge one size smaller than the standard. This is the new rule, and only applies to non-fluctuating loads.

[Marc]

I've don't remember seeing anything other than #10 for AC feed. If I would have run into a #12 on a 30amp I would have written it up. I guess I won't do that now.

It's nice being corrected before making the mistake. I guess forum participation is helpful in that respect sometimes.

Charlie, I shouldn't have second guessed you but I'm glad I did anyway.

I'm inclined to agree with you, John. Minimum ampacity may be 14.4 amps, but what is the max? As Marc says, maybe 2 or 3 times that at every startup. If the compressor seizes up, the breaker won't trip until the current reaches 25 amps or more. Running a #14 gauge feeder inside a wall and feeding it with a 25 amp breaker would be asking for trouble, IMO.

In the event of a rotor lockup or compressor seize, the automatic over-current protection built into the compressor might well activate and remove the motor from the circuit before the branch circuit breaker trips. That's by design. It's how it's intended to work. I've known this to happen much more often than a breaker trip in my 20 years in residential/light commercial HVAC.

The manufacturer calculations that yielded the specified min ampacity value are designed to prevent the development of excessive temperatures in the branch circuit wiring in the event of a compressor seize or bearing lockup.

Marc

[John Kogel]

I've don't remember seeing anything other than #10 for AC feed. If I would have run into a #12 on a 30amp I would have written it up. I guess I won't do that now.

It's nice being corrected before making the mistake. I guess forum participation is helpful in that respect sometimes.

Charlie, I shouldn't have second guessed you but I'm glad I did anyway.

I'm inclined to agree with you, John. Minimum ampacity may be 14.4 amps, but what is the max? As Marc says, maybe 2 or 3 times that at every startup. If the compressor seizes up, the breaker won't trip until the current reaches 25 amps or more. Running a #14 gauge feeder inside a wall and feeding it with a 25 amp breaker would be asking for trouble, IMO.

In the event of a rotor lockup or compressor seize, the automatic over-current protection built into the compressor might well activate and remove the motor from the circuit before the branch circuit breaker trips. That's by design. It's how it's intended to work. I've known this to happen much more often than a breaker trip in my 20 years in residential/light commercial HVAC.

The manufacturer calculations that yielded the specified min ampacity value are designed to prevent the development of excessive temperatures in the branch circuit wiring in the event of a compressor seize or bearing lockup.

Marc

Thanks, Marc. Nevertheless, the circuit breaker ought to be sized to the wire size, not the expected load. At least that is the accepted rule, AFAIK.

So a #14 gauge feeder would require a 15 amp breaker in the panel. The 15 Amp breaker exceeds the minimum of 14.4 amps, so it meets the manufacturer's requirement and it protects the wire.

There is plenty of discussion on this subject here. http://hvac-talk.com/vbb/showthread.php?t=174066

[AHI in AR]

I've don't remember seeing anything other than #10 for AC feed. If I would have run into a #12 on a 30amp I would have written it up. I guess I won't do that now.

It's nice being corrected before making the mistake. I guess forum participation is helpful in that respect sometimes.

Charlie, I shouldn't have second guessed you but I'm glad I did anyway.

I'm inclined to agree with you, John. Minimum ampacity may be 14.4 amps, but what is the max? As Marc says, maybe 2 or 3 times that at every startup. If the compressor seizes up, the breaker won't trip until the current reaches 25 amps or more. Running a #14 gauge feeder inside a wall and feeding it with a 25 amp breaker would be asking for trouble, IMO.

In the event of a rotor lockup or compressor seize, the automatic over-current protection built into the compressor might well activate and remove the motor from the circuit before the branch circuit breaker trips. That's by design. It's how it's intended to work. I've known this to happen much more often than a breaker trip in my 20 years in residential/light commercial HVAC.

The manufacturer calculations that yielded the specified min ampacity value are designed to prevent the development of excessive temperatures in the branch circuit wiring in the event of a compressor seize or bearing lockup.

Marc

Thanks, Marc. Nevertheless, the circuit breaker ought to be sized to the wire size, not the expected load. At least that is the accepted rule, AFAIK.

So a #14 gauge feeder would require a 15 amp breaker in the panel. The 15 Amp breaker exceeds the minimum of 14.4 amps, so it meets the manufacturer's requirement and it protects the wire.

There is plenty of discussion on this subject here. http://hvac-talk.com/vbb/showthread.php?t=174066

John, it seems that you're ignoring the transitory extra current draw at startup. That's why the tag specifies minimum circuit ampacity (for normal running load) as well as max breaker size to handle draw at startup.

[Jim Katen]

Thanks, Marc. Nevertheless, the circuit breaker ought to be sized to the wire size, not the expected load. At least that is the accepted rule, AFAIK.

No. Not in an air conditioning circuit.

First of all, the motor *is* providing the overcurrent protection to the wire.

Second, if the "accepted rule" you're talking about is 240.4, it contains an exception for air conditioning equipment. (240.4(G)). This section refers you to article 440 for sizing conductors for air conditioning equipment. But there's no need for that in most case. It's really easy. You just use the numbers on the data plate.

Third, if you installed a 15-amp breaker on this circuit, it would tend to trip whenever the compressor fired up.

So a #14 gauge feeder would require a 15 amp breaker in the panel. The 15 Amp breaker exceeds the minimum of 14.4 amps, so it meets the manufacturer's requirement and it protects the wire.

You'd end up with a breaker tripping all the time and you wouldn't gain any safety. If you want a larger margin of safety use a larger wire, not a smaller breaker. That will also meet the manufacturer's requirements, and reduce voltage drop. But it's not necessary for a safe installation unless there are other considerations such as high ambient temperature, etc.

There is plenty of discussion on this subject here. http://hvac-talk.com/vbb/showthread.php?t=174066

The original question is flawed and the subsequent discussion runs off into the ozone. For the purposes of a home inspector inspecting the wiring to an air conditioner, this is simple enough. Look at the data plate and, just for the AC circuit, set aside the rote rules you've learned about breaker sizing.

[plummen]

If you look at the first photo posted, the manufacturer states no bigger than a 25 amp breaker. or fuse Just above that is a line that says the minimum ampacity is 14.4. This means you can use a 25 amp breaker with #14 awg because #14 can be used with up to 15 amps. The stated ampacity is what determines the wire size, not the breaker. As far as I know (and I stand ready to be corrected) it may be the only exception to the NEC rules, and it's ok with the NEC. If you can't find a 25 amp breaker, a lot of installers put 25 amp cartridge fuses in the exterior disconnect box. Yes, you can use #12 awg or #10 awg with this as you can always have a larger than required conductor but it is more than what is required. Of course, I agree with you, using larger than required is good, at least in wiring. Also, yes, I think experience means a heck of a lot, but just because someone has done something the same way for 20 years doesn't make it right. And I just went to Home Depot, on the shelf were a GE, a Square D, and an Eaton 25 amp two pole breaker, highest price was 16.80. (http://www.homedepot.com/webapp/wcs/sto ... c=1&Ntpr=1) If you need one, I'll buy it and ship it to you for a small surcharge.

Agreed that 14 AWG & a 25A circuit breaker is code compliant, & if a 25A breaker could not be found, a fusible pullout A/C disco is cheap & then 25A fuses could be installed......

"Wire it to the minimum, overcurrent protection to the max." That is how bids are won.

?????????

[plummen]

I've don't remember seeing anything other than #10 for AC feed. If I would have run into a #12 on a 30amp I would have written it up. I guess I won't do that now.

It's nice being corrected before making the mistake. I guess forum participation is helpful in that respect sometimes.

Charlie, I shouldn't have second guessed you but I'm glad I did anyway.

I'm inclined to agree with you, John. Minimum ampacity may be 14.4 amps, but what is the max? As Marc says, maybe 2 or 3 times that at every startup. If the compressor seizes up, the breaker won't trip until the current reaches 25 amps or more. Running a #14 gauge feeder inside a wall and feeding it with a 25 amp breaker would be asking for trouble, IMO.

Simply put, the label does not say to use a #14 supply cable. Does it? [?]

Interestingly, the Canadian (CEC) rule, here for static heating loads, such as electric baseboard heating, allows us to use a wire gauge one size smaller than the standard. This is the new rule, and only applies to non-fluctuating loads.

[:-graduat

[Jim Port]

The trip curve characteristics of the breaker would take care of safely shutting down the power before the wire overheated enough to cause a fire. The higher the current over the trip value the quicker it shuts off.

[John Kogel]

Thanks, Marc. Nevertheless, the circuit breaker ought to be sized to the wire size, not the expected load. At least that is the accepted rule, AFAIK.

No. Not in an air conditioning circuit.

First of all, the motor *is* providing the overcurrent protection to the wire.

Second, if the "accepted rule" you're talking about is 240.4, it contains an exception for air conditioning equipment. (240.4(G)). This section refers you to article 440 for sizing conductors for air conditioning equipment. But there's no need for that in most case. It's really easy. You just use the numbers on the data plate.

Third, if you installed a 15-amp breaker on this circuit, it would tend to trip whenever the compressor fired up.

So a #14 gauge feeder would require a 15 amp breaker in the panel. The 15 Amp breaker exceeds the minimum of 14.4 amps, so it meets the manufacturer's requirement and it protects the wire.

You'd end up with a breaker tripping all the time and you wouldn't gain any safety. If you want a larger margin of safety use a larger wire, not a smaller breaker. That will also meet the manufacturer's requirements, and reduce voltage drop. But it's not necessary for a safe installation unless there are other considerations such as high ambient temperature, etc.

There is plenty of discussion on this subject here. http://hvac-talk.com/vbb/showthread.php?t=174066

The original question is flawed and the subsequent discussion runs off into the ozone. For the purposes of a home inspector inspecting the wiring to an air conditioner, this is simple enough. Look at the data plate and, just for the AC circuit, set aside the rote rules you've learned about breaker sizing.

OK, thanks, Jim, Marc and all.

I should say we rarely come across simple AC units here. It's our climate. We open windows for a bit of cool air. No bugs, no polluting industries. No hot sun, either. We use heat pumps a fair amount, but they have the highest initial cost of all, so they are typically found in the higher end houses. I have not come across under-sized wiring to a heat pump, but I have learned from this thread, thanks.