NEC Section 440.4(B) requires specific nameplate marking for HVAC multimotor and combination-load equipment. HVAC units containing a hermetically sealed refrigerant compressor motor and other integral loads are considered combination-load equipment. For these units, the short-circuit current rating (SCCR) for the motor controller is required to be marked on the nameplate unless 440.4(B) exception 3 applies. The marking is there so that the installer (could be the HVAC tech or the electrician or both) can ensure that the SCCR of the HVAC unit is equal to or greater than the Available Fault Current (AFC) at the HVAC unit motor controller in compliance with Section 110.10 as well as Section 440.10 which was new in the 2017 NEC^®.

Generally, rooftop HVAC units are installed with some distance to the electric panel where their circuit conductors originate. The longer the run of circuit conductor to the air conditioner, the less likely the AFC at the HVAC unit will exceed the marked SCCR on the HVAC unit nameplate.

As well, many HVAC units will have a fused disconnect switch installed adjacent to the unit. If the AFC at the HVAC unit was higher than the marked SCCR on the nameplate, one option would be to refer to the fuse charts to select a specific fuse because of its current limiting characteristics which will ensure that the fuse will never let through more AFC than the SCCR on the HVAC unit.

See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).

2014-2023 Code Language:

440.4 Marking on Hermetic Refrigerant Motor-Compressors and Equipment.

(B) Multimotor and Combination-Load Equipment. 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. The ampacity shall be calculated by using Part IV and counting all the motors and other loads that will be operated at the same time…