12.3 Branch Circuits, Conductors, Grounding & Disconnects
Key Takeaways
- Conductor ampacity for HVAC branch circuits is taken from the 75 degree Celsius column of NEC Table 310.16 because equipment terminations are rated 75 degrees Celsius.
- NEC 240.4(G) exempts air conditioning and refrigeration branch-circuit conductors from the small-conductor limits of 240.4(D), which is why a 14 AWG conductor can be protected at 30 amperes on a properly rated unit.
- NEC 210.63 requires a 125-volt, 15- or 20-ampere receptacle within 25 feet of heating, air conditioning, and refrigeration equipment for servicing.
- The equipment grounding conductor is sized from NEC Table 250.122 by the rating of the overcurrent device, not by the size of the ungrounded conductors.
- Grounding connects the system to earth for voltage stabilization, while bonding connects metal parts together so a fault current has a low-impedance path back to the source to open the overcurrent device.
12.3 Branch Circuits, Conductors, Grounding & Disconnects
[!NOTE] Where this sits in Alabama law. Alabama Administrative Code Rule 440-X-3-.09(3) makes the certified HACR contractor responsible for electrical work "to include circuit protection and wiring, from the appliance to the means of disconnect." That is the scope boundary: from the disconnect to the equipment is your work and your liability. The exam reference for it is the 2020 NFPA 70 National Electrical Code.
Conductors: Material, Insulation and Ampacity
| Property | Copper | Aluminum |
|---|---|---|
| Conductivity | Higher | About 61 percent of copper |
| Size for equal ampacity | Smaller | Two sizes larger, typically |
| Terminations | Standard lugs | Requires listed AL/CU lugs and an antioxidant compound |
| Common HVAC use | Branch circuits, whips | Feeders and service conductors |
Ampacity comes from NEC Table 310.16. Three rules govern which number to use:
- Use the 75 degree Celsius column. NEC 110.14(C) limits the conductor ampacity to the lowest temperature rating of any connected termination, and equipment lugs and breakers on HVAC gear are almost universally rated 75 degrees Celsius. THHN copper is a 90 degree Celsius conductor, but the 90 degree column may be used only for derating calculations, never as the final ampacity.
- Correct for ambient temperature. A conductor in an Alabama attic that reaches 130 degrees Fahrenheit carries substantially less than its table value; apply the correction factors printed with Table 310.16.
- Adjust for conductor fill. More than three current-carrying conductors in a raceway or cable requires the adjustment factors of 310.15(C)(1).
Voltage Drop
The NEC addresses voltage drop in informational notes rather than a hard rule, recommending a maximum of 3 percent on a branch circuit and 5 percent total from service to outlet. On a long run to a detached-garage condenser or a remote rooftop unit, voltage drop, not ampacity, usually sets the conductor size. Low voltage at a compressor raises current, raises winding temperature, and shortens life.
The Article 440 Exemption
Under the general rule of NEC 240.4(D), small conductors are limited to 15 amperes for 14 AWG, 20 amperes for 12 AWG, and 30 amperes for 10 AWG copper.
NEC 240.4(G) lists specific applications that are protected instead by the rules of their own article, and air conditioning and refrigeration equipment under Article 440 is on that list. This is why a condensing unit nameplate can legitimately read "Minimum Circuit Ampacity 14.5, Maximum Fuse or HACR Breaker 25" and be wired with 14 AWG copper on a 25-ampere breaker. The conductor is sized to the MCA; the overcurrent device is sized to the MOP, and the two are deliberately different numbers because the device is protecting against short circuit and ground fault while the motor overload protects against sustained overcurrent.
Grounding Versus Bonding
These are not synonyms, and the exam separates them.
- Grounding connects the electrical system to the earth. Its purpose is to stabilize voltage relative to earth and to limit voltage imposed by lightning or line surges. Earth is a poor conductor and does not clear faults.
- Bonding connects metallic parts together and back to the source so that a ground fault sees a low-impedance path, drives enough current to operate the overcurrent device, and clears the fault quickly.
The equipment grounding conductor (EGC) is the bonding path in a branch circuit, and it is sized from NEC Table 250.122 by the rating of the overcurrent device, not by the size of the phase conductors:
| Overcurrent device rating | Minimum copper EGC |
|---|---|
| 15, 20 amperes | 14 AWG |
| 30, 40, 60 amperes | 10 AWG |
| 100 amperes | 8 AWG |
| 200 amperes | 6 AWG |
Flexible metal conduit whips used at condensing units may serve as an equipment grounding path only within the listed length and size limits; the safe field practice is to pull a separate green EGC in the whip.
Disconnecting Means and Working Space
| Requirement | Rule |
|---|---|
| Location | Within sight from the equipment - visible and not more than 50 feet away (NEC 440.14 and the Article 100 definition) |
| Ampacity | At least 115 percent of the nameplate rated-load current or branch-circuit selection current, whichever is greater (NEC 440.12(A)(1)) |
| Mounting | Not on panels designed to allow access to the equipment, and not obscuring the nameplate (NEC 440.14) |
| Working space depth | Minimum 3 feet in front for systems 150 volts or less to ground, per Table 110.26(A)(1) |
| Working space width | 30 inches or the width of the equipment, whichever is greater |
| Headroom | 6.5 feet |
The working space must be kept clear and cannot be used for storage. Setting a condenser so close to a fence that a technician cannot stand in front of the disconnect is a violation as surely as a missing ground.
The Service Receptacle and GFCI
- NEC 210.63 requires a 125-volt, single-phase, 15- or 20-ampere receptacle outlet within 25 feet of heating, air conditioning, and refrigeration equipment, at an accessible location on the same level, for servicing. It may not be connected on the load side of the equipment disconnect.
- GFCI protection: the 2020 NEC extended ground-fault circuit-interrupter protection to outdoor outlets at dwellings under 210.8(F), a provision written to include outdoor HVAC equipment and phased in with a delayed effective date. Later code cycles narrowed and re-shaped the requirement. Because adoption in Alabama is by local jurisdiction, confirm which NEC edition your building department enforces before assuming a condenser does or does not require GFCI protection. Where it does apply, the practical field consequence is nuisance tripping on some legacy equipment, which is an equipment leakage issue rather than a reason to omit the protection.
- Nameplate governs the device type. A nameplate reading "MAX FUSE 30A" requires fuses; an HACR-rated circuit breaker may be used only when the nameplate permits a breaker.
A condensing unit nameplate reads "Minimum Circuit Ampacity 14.2, Maximum Overcurrent Protective Device 25 amperes." May 14 AWG copper conductors be used on a 25-ampere breaker?
A rooftop unit branch circuit is protected by a 60-ampere overcurrent device. What minimum size copper equipment grounding conductor is required, and what determines that size?
Where must the disconnecting means for an air conditioning condensing unit be located, and what is the minimum working space in front of it for a 240-volt system?