Inspecting Oversized "AC" Breakers on Small-Gauge Wires
by Nick Gromicko, Ben Gromicko, Jim Krumm, and Lon Henderson
If a home inspector is checking the breaker for the air conditioning unit, and it appears to be oversized in relation to the size of the wire, the inspector may make the mistake of calling it a defect when it is not. This situation is a common source of confusion because the equipment label will sometimes allow the rating of the overcurrent device to exceed the ampacity of the circuit conductors. This article will help home inspectors who check the overcurrent protection device and wiring for air conditioning and heat pump equipment, which is a task beyond the InterNACHI® Home Inspection Standards of Practice.
The International Residential Code® (IRC) and the National Electric Code® (NEC) provide an exception to the general rule for overcurrent-protection ratings of breakers and the connected wire sizes. The commonly known maximum overcurrent protection rules for breakers in relation to the wire size do not apply to air conditioners and heat pumps. For example, if a home inspector observes a 50-amp "AC" breaker on an 8-gauge wire, that may not be a defect. This article will help to explain why. Let's start with the nameplate.
Nameplate
To determine the maximum size of the overcurrent protection device (OCPD) and the minimum size of the conductors for the air conditioning and heat pump equipment, the inspector has to use the data on the equipment nameplate attached to the unit outside. The OCPD rating for the air-conditioning condensing unit and heat-pump circuits is stated on the equipment nameplate, with a minimum and maximum rating given. The nameplate will also state the minimum circuit ampacity for the branch circuit conductors.
This is a common source of confusion for some home inspectors because the equipment label may allow the rating of the overcurrent protection device to exceed the ampacity of the circuit conductors. An inspector may find a 50-amp "AC" breaker on a 10-gauge wire, for example.
But it’s probably okay; it’s likely not a defect, and the breaker will be sized larger than what the inspector thinks is permitted. The home inspector should know that the International Residential Code® (IRC) and the National Electric Code® (NEC) provide exceptions to the general rule for overcurrent-protection ratings of breakers and the connected wire sizes that are just for air conditioning and heat pump equipment.
Let’s learn about checking the size of the breaker and conductors for the air conditioning and heat pump equipment by starting with the combination-load equipment.
Combination-Load Equipment
A typical air-conditioning unit is referred to as a combination-load equipment. A typical AC unit will contain several different loads in combination that comprise the total electrical load of the equipment. This type of equipment will contain a hermetic refrigerant motor compressor, a cooling fan with a motor, and possibly a crankcase heater for the compressor. So, this type of equipment is considered a combination-load equipment.
Why is that important to know?
That’s important to know because combination-load equipment manufactured today is required by the National Electric Code (NEC) to have nameplates. The nameplate, the manufacturer’s label, provides the data needed for a contractor or inspector to check the proper overcurrent protection for the equipment, including the maximum size of the circuit breaker or fuse and the minimum circuit ampacity of the conductors (that's how much current can flow through the wire). The rule for this type of equipment is to require a wire size rated for 125% of the larger motor (RLA) plus the smaller motor (FLA) and other components.
NEC 440.4 and Nameplate Information
The National Electric Code® (NEC), Section 440.4(B) says, “Multimotor and combination-load equipment shall be provided with a visible nameplate marked with the maker's name, the rating in volts, frequency and number of phases, minimum supply circuit conductor ampacity, the maximum rating of the branch-circuit short-circuit and ground-fault protective device, and the short-circuit current rating of the motor controllers or industrial control panel.” Excerpt from National Electrical Code (NEC)®.
So, NEC requires that combination-load equipment be provided with a nameplate that gives the home inspector valuable information, including two very useful numbers:
- the minimum circuit conductor ampacity (conductor size) and
- the maximum size of the overcurrent protective device (OCPD).
Some data plates show the “Minimum Overcurrent Protective Device” rating. This rating indicates the minimum-sized breaker needed to allow the motor to start without tripping. Both minimum and maximum ratings could be valuable when inspecting the OCPD and conductors.
An Example of a Nameplate
For example, let’s assume the nameplate on the AC compressor unit is the following:
Minimum Circuit Ampacity
Code says that the branch-circuit conductors must be no less than the minimum circuit ampacity marked on the nameplate of the equipment.
The manufacturer has already calculated the conductor size to be based on the total of all of the motor loads in the combination-load equipment times 125 percent. It is not necessary for the inspector to do these calculations again. The home inspector only has to look at the label and know that the branch-circuit conductors supplying the equipment should have an ampacity equal to or greater than the minimum circuit ampacity marked on the nameplate of the equipment.
When the compressor for an air conditioner or heat pump starts, there is a surge of electrical current initially. This surge lasts a fraction of a second. It's not enough to overheat the wire, but it could trip a breaker. Modern units have their own overcurrent protection built in. It will allow the surge at startup without tripping off. So, the breaker and wire size don't need to match up according to common rules for maximum breaker size and wire gauge. So, again, for example, a home inspector may see on the nameplate a 50-amp max breaker size and find a 10-gauge wire.
Okay, but what’s the minimum circuit ampacity?
The minimum circuit ampacity is the minimum size of the wire that’s connected to the AC breaker in the electric service panelboard. That’s the minimum wire size.
2021 IRC Section E3702.11, Branch Circuits for Air-Conditioning and Heat Pump Equipment, says, “The ampacity of the conductors supplying multi-motor and combination load equipment shall be not less than the minimum circuit ampacity marked on the equipment." The branch-circuit overcurrent device rating (the rating of the overcurrent protection device, the rating of the OCPD) shall be the size and type marked on the appliance. [NEC 440.4(B), 440.35].” Excerpt from the International Residential Code (NEC)®.
Okay, so from the nameplate, home inspectors can expect to see at the electric service panelboard:
- the minimum size of the wire connected to the AC/heat pump breaker, and
- the maximum size of the OCPD identified as the AC/heat pump breaker at the panelboard.
So, look at the example nameplate again. The minimum circuit ampacity marked on the equipment nameplate is 30.40A. So, what’s the minimum wire gauge? Should it be 10, 8, or 6 AWG? Why does a home inspector think it should be 8-gauge? That’s because home inspectors have been trained that the maximum size breaker connected to an 8-gauge wire is 40 amps. Assuming that we need to round up the 30.40A on the nameplate because 30.4A is greater than just 30 amps. So, if we round up 30.40A to 40 amps, then the maximum breaker size for an 8-gauge wire is 40 amps. Right? Sounds good, right?
That's Incorrect.
Look at the example nameplate again. It says “minimum circuit amps.” Remember, we looked at 2021 IRC Section E3702.11, Branch Circuits for Air-Conditioning and Heat Pump Equipment. It says, “The ampacity of the conductors supplying multi-motor and combination load equipment shall be not less than the minimum circuit ampacity marked on the equipment.”
It’s talking about “the ampacity of the conductors.” That’s what’s on the nameplate.
So, what’s the ampacity of the conductors?
We can take a look at the 2021 IRC Code, Table E3705.1 Allowable Ampacities of Conductors.
Look at the 75°C column. That’s the most common temperature used for most equipment terminations where ampacities of 100 or less are involved, and where the HACR breakers are marked for use with 75°C rated conductors at 75°C ampacities. If Romex® is used, according to NEC 334.80 Ampacity, the 60°C column should be used. But let's use the 75°C column for this article. Move down to the row with 35 amps (we round up 30.4A to 35A for safety). Now, look at the first column in the 35A row, and we see 10-gauge. 10 gauge is the minimum wire size for the 35 amp breaker.
HACR Breaker 75°C
Okay. So, the minimum wire size is 10-gauge. Not 8-gauge. Got it. The ampacity of the conductors supplying multi-motor and combination load equipment is 10-gauge, and they are not less than the minimum circuit ampacity marked on the equipment (because we checked Table E3705.1). So the wire at the panelboard should be at least 10-gauge in size. Let's check.
Check the Conductors at the Panelboard
Let’s go back to the example above and check the conductor size. Keeping with our example, if the home inspector looks at the size of the conductors that are connected to the "AC" breaker at the electric service panelboard, the inspector should expect to see a minimum 10-gauge wire connected to the AC breaker. Why? Because 10 gauge is the minimum circuit ampacity of the conductors in relation to the minimum circuit amps of 30.40A on the data nameplate. That’s the minimum conductor size in relation to that nameplate data of 30.4A (which is the minimum circuit amps on the nameplate) and according to 2021 IRC Table E3705.1.
Standards of Practice
Whew. That’s a lot of work for a home inspector. This is way beyond the scope of a home inspection. The home inspector is not required to check or confirm the data on nameplates or labels of manufactured equipment. The home inspector is not required to find overfusing problems or confirm the proper size of conductors and breakers. Home inspectors should be familiar with the requirements and exclusions of the InterNACHI Home Inspection Standards of Practice at www.nachi.org/sop.
What about the nameplate's maximum breaker size?
From our example, we determined that 10-gauge is the minimum size of the conductors that we should see at the electric service panelboard. What about the maximum size of the fuse or circuit breaker identified as the AC/heat pump breaker at the panelboard?
Maximum Fuse or Circuit Breaker Size
Let’s go back to the example nameplate above. We determined that 10-gauge is the minimum size of the conductors (based on the minimum circuit ampacity). The maximum fuse or circuit breaker size on the nameplate is 50 amps. 50 amps. Again, home inspectors have been trained that a maximum 50-amp breaker should be connected to a 6-gauge wire (not 10-gauge).
This inspector training is based on 2021 IRC Table E3705.3.3 or NEC 240.4(D), overcurrent-protection rating for small conductors.
- The maximum overcurrent-protection-device rating shall not exceed the conductor's allowable ampacity determined by the application of the correction and adjustment factors in accordance with Sections E3705.2 and E3705.3.
Okay, so in our example, the inspector should expect to see at the breaker identified as the AC/heat pump breaker at the panelboard:
- a minimum 10-gauge wire (based on the minimum circuit ampacity), and
- a maximum fuse or circuit breaker size of 50 amps (based on the nameplate data).
If the inspector sees a 10-gauge wire connected to a 50-amp breaker at the panelboard, that seems to be an overfusing defect. The maximum OCPD on a 10-gauge wire should be 30 amps. Not 50, according to the 2021 IRC Table E3705.3.3 or NEC 240.4(D), right? But the nameplate says the maximum breaker size is 50 amps. So, what’s going on?
There's an Exception to the Rule
There’s an exception to the general rule of overcurrent protection ratings of breakers for small conductors. And it’s an exception just for air conditioning and heat pump equipment. And it appears in NEC 240.4 and 2021 IRC E3705.5.3. Let's look at NEC 204.4.
NEC 240.4 Unless Otherwise Permitted
In the NEC 240.4, Protection of Conductors, we read, “Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in NEC 310.15 (or IRC Table E3705.1 Allowable Ampacities) unless otherwise permitted or required in NEC 240.4(A) through (G).”
Whew. That’s a mouthful. But here’s what it means. There’s an exception that applies to all of this and straightens out all of these apparent overfusing, over-sizing problems.
And so, if we look at the exception at NEC 240.4(G) Overcurrent Protection for Specific Conductor Applications. It says, “Overcurrent protection for the specific conductors shall be permitted to be provided as referenced in Table 240.4(G). Specific Conductor Applications. Air-conditioning and refrigeration equipment.”
So that’s the exception, as stated in NEC 204.4. What about 2021 IRC E3705.5.3?
2021 IRC E3705.5.3 says, “Except as specifically permitted by Section E3705.5.4, the rating of overcurrent protection devices (size of the breaker) shall not exceed the ratings shown in Table E3705.5.3 for the conductors specified therein. [NEC 240.4(D)]
And what’s E3705.5.4?
IRC Section E3705.5.4 is titled “Air-Conditioning and Heat Pump Equipment.” And it says, “Air-conditioning and heat pump equipment circuit conductors shall be permitted to be protected against overcurrent in accordance with Section E3702.11. [NEC 240.4(G)]." And E3702.11 (NEC 240.4(G) is the exception to the rule, particularly for air-conditioning and heat pump equipment.
And E3702.11 is for branch circuits for air-conditioning and heat pump equipment. It says, "The ampacity of the conductors supplying multi-motor and combination load equipment shall be not less than the minimum circuit ampacity marked on the equipment. The branch-circuit overcurrent device rating shall be the size and type marked on the appliance. [440.4(B), 440.35]. For these circuits, it is necessary to know the nameplate information in order to determine the proper size conductors. The equipment label will dictate the required branch circuit ampacity and rating of the overcurrent device."
Whew. There's the exception to the rule.
It’s Simply an Exception
So, to simplify it all, air conditioning and heat pump equipment are the exceptions to the rule for home inspectors who are looking at the OCPD of the AC or heat pump unit in relation to the size of the wire connected to the equipment.
The overcurrent protection device rating for air-conditioning condensing unit and heat-pump circuits can be seen on the equipment label, with a minimum and maximum rating given. The label will also state the minimum circuit ampacity for the branch circuit conductors. This situation is sometimes a source of confusion for home inspectors because the equipment label will sometimes allow the rating of the overcurrent device to exceed the ampacity of the circuit conductors. But that’s okay because the IRC and NEC codes provide the exception to the general rule for overcurrent-protection ratings of breakers and the connected wire sizes. And knowing that exception and applying it will help home inspectors do better inspections.
Maximum Rating of the OCPD
So, let’s assume that a home inspector is at the electrical service panelboard with the dead front cover removed. And the inspector is looking at the breaker identified as the AC or heat pump breaker for the outdoor compressor unit and the wire conductors connected to that breaker. And the inspector notices the size of the conductor in relation to the size of the breaker.
Before the inspector can make any comment about the expected size of the conductors based on that observation, it is necessary for the inspector to know the nameplate information on the equipment. The manufacturer’s equipment label will dictate the required branch circuit ampacity (minimum conductor size) and maximum rating of the overcurrent protection device (maximum breaker size).
Fuse on the Label
Sometimes, the manufacturer of the combination-load equipment will specify fuses as the OCPD. If the nameplate says fuse only, the manufacturer has determined that only a fuse can provide the proper overcurrent protection for the air-conditioning condensing unit and heat pump unit. The use of a circuit breaker would be a code violation and a defect.
HACR
Most manufacturers permit either fuses or HACR circuit breakers as the OCPD. If the equipment nameplate says “maximum fuse size” or “HACR circuit breaker,” then the equipment has been tested for use with either. The HACR breaker is a type of circuit breaker that is listed for group applications. In other words, the breaker is able to supply proper protection for both the larger compressor motor circuit as well as the components of the smaller fan motor circuit.
HACR
Maximum Overcurrent Protection Device (OCPD) Rating
The “maximum overcurrent protective device” rating in amps is the other important number on the AC equipment data plate. The overcurrent protection device marked on combination-load equipment is marked “maximum” such as “maximum fuse or breaker size.” This means that the specified size of the OCPD can not be exceeded.
Another Example
Let’s do another example.
In this example, let’s assume the nameplate states the minimum circuit ampacity is 24.0 amps, and the maximum overcurrent device is 40 amps. Based on the nameplate data, the conductors are required to be capable of carrying 24.0 amps.
We can take a look at the 2021 IRC Code, Table E3705.1 Allowable Ampacities.
We can determine that 12-gauge copper is the minimum size for the circuit conductors.
In this example, the nameplate states the maximum overcurrent protective device is 40 amps. And a home inspector may mistakenly think that if the nameplate says 40-amp breaker, and there’s a 40-amp breaker at the panelboard, and it is connected to a 12-gauge wire, then that’s a defect. The size of the breaker is too big for the 12-gauge wire because the home inspector has been trained that the maximum size breaker for a 12-gauge wire is 20 amps, according to the 2021 IRC E3705.5.3.
And 2021 IRC E3705.5.3 says, “Except as specifically permitted by Section E3705.5.4, the rating of overcurrent protection devices (size of the breaker) shall not exceed the ratings shown in Table E3705.5.3 for the conductors specified therein. [NEC 240.4(D)].” That is the exception for the following table.
- The maximum overcurrent-protection-device rating shall not exceed the conductor allowable ampacity determined by the application of the correction and adjustment factors in accordance with Sections E3705.2 and E3705.3.
There’s an exception to the general overcurrent-protection rating rule. And it’s an exception just for air conditioning and heat pump equipment. And it appears in 2021 IRC E3705.5.3 and NEC 240.4.
In this example, we can:
- determine that 12-gauge copper is the minimum size for the circuit conductors,
- see the nameplate states the maximum overcurrent protective device is 40 amps, and therefore, and
- expect to see a 40-amp AC breaker at the panelboard.
Let’s assume that in this example, the conductor for the AC unit is 12 gauge, as observed by the home inspector at the electrical service panelboard. It seems as though the 12-gauge conductors are improperly protected because they are connected to a large 40-amp breaker. But there’s an exception in the code for air conditioning and heat pump equipment.
And the 40-amp breaker on a 12-gauge wire is okay. It’s permitted by code, because of the exception for air conditioning equipment and heat pump units.
You see, in 2021 IRC, Table E3705.5.3 provides the maximum overcurrent device rating for small-size conductors regardless of the allowable ampacity. This section provides an extra level of safety by placing a conservative and absolute cap on the overcurrent device ratings for the smaller conductors used throughout the dwelling.
From this section of the code, home inspectors learn that a 15-amp circuit breaker is used on circuits with size 14-AWG conductors, a 20-ampere circuit breaker with size 12-AWG conductors, and a 30-ampere circuit breaker with size 10-AWG conductors. And so on. And there’s an exception as allowed by Section E3705.5.4.
And if you go to that Section E3705.5.4, it’s titled “Air-Conditioning and Heat Pump Equipment.” That’s the exception to the general rule in 2021 IRC E3705.5.3 and NEC 240.4(D) in relation to the rating of overcurrent protection devices (size of breakers) not exceeding the ratings for conductors (size of wires) connected to those breakers.
Home Inspection Example 1
Here are two inspection images taken during a home inspection.
In the first image of an older air conditioning unit, the minimum circuit amps on the nameplate is 21.5. According to the 2021 IRC Code, Table E3705.1 Allowable Ampacities, the inspector should expect to see a 12-gauge wire minimum at the panelboard.
The Maximum Circuit Breaker on the nameplate is 30 amps. The inspector should see at 30-amp breaker maximum at the panelboard.
At the panelboard, the inspector saw a 10-gauge wire, which is good because 12-gauge is the minimum. And the inspector saw a 30-amp breaker. That's good, too. Because the nameplate required a maximum breaker size of 30-amps. So, no defects were observed here.
Home Inspection Example 2
Here are two inspection images taken during a home inspection.
In the image of a newer air conditioning unit, the minimum circuit amps is 17.9. According to the 2021 IRC Code, Table E3705.1 Allowable Ampacities, the inspector should expect to see a 14-gauge wire minimum at the panelboard.
The Maximum Circuit Breaker on the nameplate is 30 amps. The inspector should see at 30-amp breaker maximum at the panelboard.
At the panelboard, the inspector saw a 10-gauge wire, which is good because 14-gauge is the minimum. And the inspector saw a 30-amp breaker. That's good, too. Because the nameplate required a maximum breaker size of 30 amps. So, no defects were observed here.
Conclusion
If a home inspector is checking the breaker for the air conditioning unit, and it appears to be oversized in relation to the size of the wire, the inspector may make the mistake of calling it a defect when it is not. Home inspectors can correctly inspect the overcurrent protection device and wiring for air conditioning and heat pump equipment. The commonly known maximum overcurrent protection rules for breakers in relation to the wire size do not apply to air conditioners and heat pumps, because there is an exception provided by the IRC and NEC.
The overcurrent protection device rating for the air-conditioning condensing unit and heat-pump circuits is stated on the equipment label, with a minimum and maximum rating given. The nameplate will also state the minimum circuit ampacity for the branch circuit conductors. This situation is commonly a source of confusion because the equipment label will sometimes allow the rating of the overcurrent device to exceed the ampacity of the circuit conductors. The home inspector should know that the IRC and NEC provide an exception to the general rule for overcurrent-protection ratings of breakers and the connected wire sizes. And knowing that exception and applying it will help home inspectors do better inspections.
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More inspection articles like this.
InterNACHI's free, online How to Perform Electrical Inspections Course.
Mike Holt, Air Conditioning Circuit Sizing, NEC 440.4(B), NEC 334.80, and 240.4(G).
NEC 334.80 Ampacity says, "The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60°C (140°F) rated conductor."
UL Heating Cooling Guide, page 17, number 25, "For some equipment, the testing and construction are based on the use of wiring with 75°C insulation. However, most equipment, where ampacities of 100 or less are involved, is marked for use with 75°C rated conductors at 75°C ampacities."
