Art. 440, Part I provides the NEC general requirements for air-conditioning and refrigerating equipment. This article has an unusual aspect to it, compared to other NEC articles — it’s essentially a supplement to Art. 430 (motors). It covers a special type of motor, namely ones that are hermetically sealed. They are hermetically sealed because they are immersed in the refrigerant the motor-compressor system is pumping.
So, you won’t find all the hermetic motor requirements in Art. 440. Because they are motors, they are covered by Art. 430, more or less. You apply Art. 430, except as amended by Art. 440.
Always look at the nameplate before installing; it will provide information such as the following [440.4]:
- Manufacturer’s name, trademark, or symbol.
- Identifying designation.
- Phase, voltage, and frequency.
The motor nameplate should also show the rated-load current (in amperes). If it does not, then look at the nameplate of the equipment in which the motor compressor is used. You will need this value to determine the rating of the disconnecting means, branch-circuit conductors, controller, branch-circuit short circuit and ground-fault protection, and the separate motor overload protection [440.6(A)].
You will find other useful information on these nameplates. It’s a good idea to photograph them and attach the images to the work report. The manufacturer also must mark the motor controllers with information [440.5]; the requirements echo those of 440.4.
To size the conductors, use Table 310.16 through 19, or calculate per 310.14 as applicable [440.6].
What if you have more than one motor in the system? Do you use the highest-rated motor rule, as in Art. 430? Yes, use the hermetic motor with the highest rated-load current [440.7]. But how do you identify the largest motor that isn’t hermetic? Use the full-load current corresponding to the motor horsepower rating selected from Table 430.248, 430.249, or 430.250.
Many HVAC units are installed on a roof. All such units must have an equipment grounding conductor of the wire type in outdoor portions of metallic raceway systems that use compression fittings [440.9]. If the building has a lightning protection system, these units must also be bonded to it to prevent flashovers.
There’s a condition under which you cannot install motor controllers or industrial control panels of multimotor and combination-load equipment. The condition is the available fault current exceeds that equipment’s short-circuit current rating per 440.4(B).
