We are buying a 4 yr old house and when the inspections were done,
the inspector said that the small compressor (has zoned AC with 2 compressors) has a 40 amp breaker but according to the plate on the unit,
it should only have a 20 amp breaker. He said this needed to be changed
as it posed a hazard if the unit overheated and the breaker would not trip.
Does this sound right to you guys?

Thanks,
Jack

 

It sounds right, especially if the inspector said to change it. 20 amp will use 12ga wire, if 40amps try to go through it you could have a little fire.

 

AFAIK the breaker is used to protect the wire. The Compressor itself should have overload circuits to protect it. Check the wire size.

 

overcurrent protection is based on wire size, If it has anything smaller than #8 wire, then the breaker is too big, But if it has #8 or larger it would be acceptable and above and beyond code, But the inspector would have the last say.

 

oops, I'm sorry nameplate rating , does that read 20A? that seems low, I'm not sure what exactly zoned AC means, but a small, say 2.5ton central air would be like 30A #10 WIRE, and above 2.5 would be 40A #8 copper. I'm not sure how this compares to your situation. Is that 20 FLA (full load amps) If so it would have to be #10 wire and fused at 30a or start up currents would continually trip the breaker, or just when it just slightly heated up. Generally fused about 20% higher and the next higher fuse size?

 

Check the labels on the units
these will tell you the MAX fuse size
Both inside and outside units
the compressors have probably been replaced with more
effiecient units than were there originaly
I work in remodeling and regularly replace breakers
with lower rated ones due to this
the old axiom of tonnage to amps no longer applies
today. your local building inspector (city or county) will always refer
to this label due to the wide range of units with differant
ratings. the only requirement on the wire is that of min. size, if larger all the better

 

Like MHG and witdog2020 said, read the label on the unit CAREFULLY. Home inspectors are not electrical inspectors and THEY have no say, other than to help the buyer get a lower price from the seller.

Hermetic motor compressors are one of the most difficult loads to start, so there is a whole section in the NEC on this. There is a difference between running load amps and max fuse size. The home inspector may have cited the wrong entry from the label. 20 amps is an awfully small breaker for any AC compressor -- we're talking maybe 10 running amps, which would be only enough for a 1.5 ton compressor, if that. Compressors have their own thermal and overload protection built in, so the justification offered by your "inspector" is a bit off the mark.

The "max fuse size" on the label must be complied with; this ensures that the breaker protects the compressor motor controller against shorts and really severe overloads not so much the compressor motor itself from "overheating".

If the existing wiring is #8, and if the breaker really is over the max fuse size, and if the disconnect at the unit has provisions for overcurrent protection, you have the option of installing an appropriate fuse or HACR type breaker in the disconnect, rather than back at the panel supplying the branch circuit.

 

20 amps does sound low, and 40 amps thru too small a wire will cause a fire eventually..............it could also be that a 40 amp breaker/ larger wire is required to deliver 20 amps of current the distance away from the panel the unit is. There should also be a cutoff/breaker box within 3 feet of the unit. regardless of what is in the panel.......this is were a 20 amp breaker would protect the unit. As long as the wire size is sufficient it would psoe no problem. im no electrician but am construction project manager, not that it means anything i have some exp with electrical............and inspectors, some are experienced, some are dumb as rocks. i would call alicendsed electrician to inspect not an inspector........take anything they say with a grain of salt, and read the fine print......most say they are "visual" inspections only and cant be held liable for anything!!!!!!!!

 

PS i was referring to Home inspectors, and not all of them deserve to be slandered(just most)......not city code inspectors. They do have the last word, but most any licensed electrician in your area will know what is/is not acceptable by local codes. they would be able to inspect the system and coordinate with the electrical inspector if anything needs to be changed............a permit would be required thus an inspection.

 

Thanks for all the input guys. We will move in April 17, so then I will be able to further
see if an electrician is needed. It does have a breaker box for each unit right
next to each compressor, like Jamar mentioned. The small unit serves one bedroom
and the large one serves the rest of the house.

Thanks,

Jack

 

i'd get an electrician to eyeball it ASAP, if u havent closed on the house yet its an issue to take up with current owners, even if you have closed might take some time to get electricians out and the work done, that way u are good to go when u move in on the 17th........sure wouldnt wanna move in if its a fire hazard.

 

fefarms is on track. This is the one instance where wire is protected by a breaker that is way too large. On AC compressor unit the breaker is sized to protect against locked rotor amps while still allowing high starting current. Internal to the compressor are thermal overloads that will protect the compressor from load induced overheating and thus also protects the wires from overload. The only thing the breaker has to protect the wires from is a short circuit. The wires are sized for the running current of the compressor. As an example my AC has a 50 amp breaker and #10 wire. This is all on the nameplate.

Breaker sizing for normal multiuse/multiload circuits is to protect the wire from overloads.

I believe the home inspection is to cover the bank's butt. Mine was required by the lender not by me. He and I both missed something that cost me $2k.

 

I work with AC units every day. The compressor may have been tripping the 20a breaker, so someone replaced it with a 40a breaker. Seen it done twice. I would have the AC unit, wiring and breaker checked. What size is the unit?

 

Is this sarcastically speaking? You are using #10 wire fused at 50A? If the running current or FLA is 20A you wouldn't size the breaker at 20A, and use #12 wire. You would run #10 and fuse it at 30A.

 

It is entirely possible to have a safe and code compliant installation which has #10 wire fused at 50 amps, but only for motors or motor-compressors. See article 430 and article 440 of the NEC. Remember that motors (and motor compressors) have overload protection in the motor controller or in the motor itself, which also protects the branch circuit conductors from sustained overcurrent. The branch circuit breaker back in the panel provides short circuit protection. It needs to be sized significantly above the full load amps to allowo reliable starting. (Article 430 allows an inverse time branch circuit breaker to be sized at up to 250% of the full load amps of the motor.)

A 20 FLA MOTOR circuit is allowed to use 12AWG wire and up to a 50 amp branch circuit breaker. (Normally 12AWG circuits are limited to a 20 amp breaker no matter what type of insulation you have).

Newer motors and motor driven appliances have data plates that really make clear their requirements for sizing wiring and overcurrent protection. The minimum circuit ampacity and max fuse size is right there in plain language.

As a practical matter, I tend to upsize the branch circuit wiring above the minimum circuit ampacity stated on the data plate, just to improve starting performance. So a 20FLA motor branch circuit I would normally wire with 10AWG wire. I would try a 30 amp breaker, but if the breaker tripped during starting I'd have no problems bumping it to a 40 amp breaker. If false tripping wou;d represent a signficant hazard or inconvenience (no heat to the house for example), I'd put the 40 amp breaker in from the outset.

Remember, again, this is for MOTOR circuits falling under article 430. Don't be trying this for your electric water heater, etc.