I was on a condo inspection the other day and found the following issue. I found a HVAC compressor without a heat pump with a 50 Amp breaker wired with #10 awg copper wiring. I stated in my report that the wiring was to small and was a safety issue and that an electrical contractor should evalaute and further evalaute and cure the situation.
The response from the contractor was that in this particualr case, this was acceptable given that it was a motor and peak power…blah blah blah…Is any of this right? I think I was getting some smoke up the keister because if this is the case in the 725 condo’s then he is gonna have some splaining to do Lucy…Just need to know if that in ANY case is a 50 amp breaker allowed and safe with a #10 AWG copper wire? Thanks!
For motor loads (such as an AC compressor) the breaker only provides short circuit protection. The overcurrent/overload protection is built into the AC unit. There often appears to be a great disparity between the wire gauge and the rating of the breaker for motor loads. Motor loads are “the exception to the rule”, many times.
Greg rightly points out what is probably written on the AC unit data plate. The argument starts and ends with the data plate on the unit. That is your next stop.
No. In fact, with regard to short circuit protection, the trip curve for most breakers 20 amp through 100 amp is nearly the same. Overload is a different story. In the case of an AC unit, the overload protection is built into the AC compressor. The breaker is only providing short circuit protection, and is purposely oversized to assure that it will not nuisance trip during compressor startup. There are rules as to how much oversized it may be, on the off chance that there would be an overload (partial low-level short circuit) in the wiring between the breaker and the AC unit. They only want the breaker a few sizes larger than “normal” to increase the chances that it will trip if there’s a wiring malfunction that is not related to the compressor itself.
Marc I agree with what you are stating but you left out one word that might make it easier to understand for the non-A/C folks. The compressor is protected by a thermal overload embedded in the windings of the compressor sensing heat only which can be generated from faulty electrical current or excessive heat from the freon side of the compressor.
I know of No A/C MFG that does not list the minimum and maximum circuit amps on the name plate data. I can not tell you how many times I have found a 60 amp breaker installed on a A/C unit when it stated right on the name plate Max 40 amp
You will still probably have short circuit protection with the 60 (depending on circuit length) but what you won’t have is protection for the compressor in a locked rotor situation. In a case where you could have just fixed this with a $10 capacitor the compressor will burn up and you will have a huge bill (assuming the tech doesn’t sell you a new system anyway).
If the manufacturer is doing his job the LRA will trip the breaker if it sits there for several seconds but it won’t trip on a normal start where LRA is less than a second. There is quite a bit of engineering that goes into that label.
The only place in the NEC where they say you can set the O/C device to hold LRA indefinately is for a fire pump. That is another breed of cat entirely. The thinking there is you can suck a bass up out of the lake, lock the firepump rotor, cook it down to bouillabaisse and send it on down the line.
Overcurrent protection devices must have an interrupting rating sufficient for the maximum possible fault circuit available on the line side terminals of the equipment.
**Conductors **must be protected against overcurrent in accordance with their ampacity. For example, a 10 AWG conductor is protected by a 30 amp breaker
Overload devices must be provided to protect motors, motor control apparatus and branch circuit conductors against excessive heating due to motor overloads and failure to start. That overload protection device is sized between 115% to 140% of the motor name plate current rating.
The branch circuit, short circuit and ground fault protection device should be sized sufficiently large enough so that the motor circuit, short circuit devices are capable of carrying the motor starting current. This is accomplished by sizing a circuit breaker at 250% of the motor full load amp rating.
A 5 hp, 240 V single phase motor the service factor of 1.16 may have a current rating of 28 amp’s.
The overload protection device must be sized no more than 125% of the motor nameplate current.
Breaker size: 28 amps X 1.25 = 35 amps
The short circuit protection device is sized no greater than 250% of the motors full load current rating.
Branch circuit short circuit device: 28 amps X 2.50 = 70 amps
This explains why larger circuit breakers are used on appliances that do not draw that much current during operation and how nameplate data is achieved.
However, branch circuit protection must protect the conductor from overheating during the startup amperage draw or overloaded condition. You cannot undersize the wire and oversize the breaker.
**(D) Small Conductors. **Unless specifically permitted in 240.4(E) or 240.4(G), the overcurrent protection shall not
exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG,
and 30 amperes for 10 AWG copper; or 15 amperes for
12 AWG and 25 amperes for 10 AWG aluminum and
copper-clad aluminum after any correction factors for
ambient temperature and number of conductors have
**[FONT=Times-Bold]size=2 Overcurrent Protection for Specific Conductor
Applications. **Overcurrent protection for the specific conductors
shall be permitted to be provided as referenced in
**[FONT=Times-Bold][size=1]Table 240.4(G) Specific Conductor Applications
Conductor Article Section
**Air-conditioning and refrigeration equipment circuit conductors 440, Parts III, VI
Capacitor circuit conductors
460 460.8(B) and 460.25(A)–(D)
Control and instrumentation circuit conductors (Type ITC)727 727.9
Electric welder circuit conductors 630 630.12 and 630.32
Fire alarm system circuit conductors
760 760.23, 760.24, 760.41, and Chapter 9, Tables 12(A) and 12(B)
Motor-operated appliance circuit conductors
422, Part II Motor and motor-control circuit conductors 430, Parts III,
IV, V, VI, VII
Phase converter supply conductors 455 455.7
Remote-control, signaling, and
power- limited circuit conductors 725 725.23, 725.24,
725.41, and Chapter 9, Tables 11(A) and 11(B)
Secondary tie conductors450 450.6
OK…see…CODE made that more than it needed to be…if the Nameplate says Minimum Ampacity 20A and Maximum OCPD is 40A…then you can size the conductors to it for 20A and size the OCPD at 40A…be done with it.
Posting CODE on that one just…well…is way to involved…
Ask him for the SIGNED OFF permit from the Building Dept. or State Electrical Dept. and then call them yourself and ask what they have to say about it. In YOUR DEPT, Is a 50 amp breaker, 10 gauge wire ok in your book? Simple and to the point.
I WOULD and have many times over, written it up as a safety issue.
In who’s dept?? In the “dept” of ANY licensed electrician or electrical inspector it is most certainly OK, as has been stated many times in this thread.
Because you persoanlly feel it is not “OK” you cannot write it up as “unsafe”, simply becasue you do not know all the aspects of the codes for the things you are inspecting.
See above reply.
This is an incorrect and unfair action directed at the installer.
I agree that the wire may perform as intended even though undersized. Under current building and TREC standards, inspector are to report deficiencies in electrical conductors and over current devices. Inspectors are not required to determine manufacturer specs or other circumstances under which under sized electrical conductors are acceptable. I would expect our company inspectors to report any occurrence of undersized electrical conductors observed. By doing so, we pass the liability of any failure on to the manufacturer, appliance specialist, cooling specialist or electrical expert.
Having said all that, the key in the thread is the fact that the label was legible and stated "minimum branch circuit ampacity 30a”.
Either way, inspectors are “generalists” not specialists, at least in Texas. I would prefer to air on the side of caution, report the possibility of an issue and pass the liability on to a specialist.