AC Condenser Typical Label

  The issue of an AC disconnect circuit being the wrong amperage or capacity rating for the unit comes up often in a lot of inspections. So, what is it?

AC manufacturers place a label on the Air Conditioning condensers that detail all the unit specifications as well as the electric service requirements. One of the specs for the electrical service is the maximum allowable amperage of the circuit breaker or fuse disconnect. The label also lists the minimum amperage capacity required for the conductor rating.

The minimum and maximum allowable amperage capacity of the disconnect and conductors are provided to allow the installer to choose a breaker or fuse disconnect that will be within the maximum rating required and the minimum rating for the conductor size.

The electric service disconnect primary function is to cut the electric service to the condenser in the event of a short circuit, overheating, or other malfunction. If the breaker or fuses installed are larger in capacity than the maximum allowed by the manufacturer specs, the disconnect will typically not trip or blow a fuse because it will withstand a larger load on the circuit.

For example, if the maximum allowable size of the circuit breaker is 35 amps, installing a 50 amp breaker will be against the maximum allowable rating of the condenser. If the 35 amps is the maximum amperage the condenser components will withstand before damaging the unit permanently, installing a 50 amp breaker as a disconnect would not allow the breaker to trip or automatically cut the electric service to the condenser until the load of the condenser exceeds 80% of the capacity of the breaker. For a 50 amp breaker it would be about 40 amps load before it would trip. ***

On the opposite side is the minimum conductor size required (wire size). If a condenser requires a minimum of 18.2 amps rating for the conductor, installing number 12 wiring would suffice for the unit but a number 10 would probably work better. However, number 14 wires rated for only 15 amps would not be appropriate ***

In technical terms, the rating of the breaker recommended by the label is about 125% of the RLA (Running Load Amperage) of the compressor and the condenser fan FLA (Full Load Amperage). The idea behind the rating specified by the label is so that the breaker trips in the event of a short circuit, a ground fault, etc. but the breaker should not trip with the starting loads of the unit which are momentarily higher than the RLA (Running Load Amperage) of the unit when it first gets itself started. Typically about 6 electrical cycles or 1/10^th of a second .***

It is not unusual to see a label for an AC condenser with a minimum of 18.2 amps for the conductor rating and a maximum of 32 amps for the over current protection device. So installing a breaker size of 30 amps for an AC condenser with a maximum rating of 32 amps and number 12 wiring for the conductor would be acceptable. However, installing a 40 amp breaker or fuse disconnect and number 14 wiring would not be.

Why is the wrong breaker size installed in the disconnect on the first place?

There are several reasons for this to happen. Among them, some times in new construction, the electrician will install a larger breaker for the condenser than what is specified without checking the condenser for the correct size needed. Either because he installed the electrical components before the AC was installed, or he did not read the plans for the correct size, or he just did not have the correct size in the truck.

Other reasons range from a home owner not knowing about the rating of the unit and just installing the first breaker that he/she could fit in the box, to actual electricians saying the larger amperage breaker is fine, even though the label says not to exceed the maximum recommended.

Label specs 20.8 minimum circuit rating and 35 amps maximum breaker size.

This last point happened recently after I found a 40 amp breaker as the disconnect while the condenser label called for a maximum rating of 35 amps breaker disconnect (See photo at left). The correct breaker size for this unit would have been a 30 amp breaker. However, the listing agent contracted an electrician that explained to him that even though the label called for a breaker no more than 35 amps, the 40 amp breaker would be the one adequate for the unit.

What does the code say?

The NEC ® (National Electrical Code) 1999 & 2002 NEC440-4B in a nutshell says that if the unit has a label with specifications by the manufacturer for the maximum disconnect and circuit rating, no changes should be made to alter those specs. The wiring and disconnect device rating should be per the label not the NEC tables unless the table is directly listed by the label.

The IRC (International Residential Code) says the following: “E3602.11 Branch Circuits for Air Conditioning and Heat Pump Equipment. The ampacity of the conductors supplying multi-motor and combination load equipment shall not be less than the minimum circuit ampacity marked on the equipment. The branch-circuit over-current device rating shall be the size and type marked on the appliance and shall be listed for the specific purpose.”  In other words, DO NOT change the conductor or disconnect breaker or fuses from what is written on the label. ***

OK, so how can it be fixed?

Assuming the wiring for the unit is correctly sized for the amperage capacity required by the condenser label, changing the breaker for one that meets the rating of the unit would correct this.

If the wiring for the AC circuit is under rated (i.e. No. 14 wire rated for 15 amps is installed for a 20.2 amp rated circuit that needs to have number 10 wiring), then replacing the wiring may also be needed.

Who can do this?

For any electrical work needing to handle 220 volts such as the circuit of an AC disconnect, the best and safest option is to hire a licensed “qualified” electrician. I place “qualified” in quote marks because having an electrician that claims to be licensed, is not the same as having an electrician that knows what he/she is doing. Or at the minimum, like in the case I described above, knows how to read and follow specs on a label.

***(A full description of the over-current protection vs. short circuits and ground faults in relation to AC condensers and compressors as well as the different types of devices required by the labels is described in the article titles “AC Condensers, Understanding over-current protection.”)