Hermetic motors, which are sealed units that operate immersed in refrigerant, are at the heart of air conditioning and refrigeration systems. Their specialized behavior means they cannot be treated like standard engines. That’s why NEC Section 440 exists: to supplement Section 430 and other NEC Sections with specific rules for short circuit protection, conductor sizing, overload protection, and disconnecting means in heating, ventilating, air conditioning (HVAC) and refrigeration applications.
This article focuses on single- and multi-motor compressors, especially those integrated into window air conditioning units, chillers, split systems, and packaged commercial HVAC equipment.
What does NEC Section 440 cover?
Article 440 applies to the installation of:
Hermetic refrigeration engine compressors
HVAC and refrigeration systems using sealed motor compressors
Room air conditioners (wired and plugged)
Equipment that combines compressors and other loads (fans, pumps, control panels)
While Section 430 still governs general engine rules, Section 440 provides overrides and additions specific to refrigeration and air conditioning loads. Some equipment, such as refrigerators or water coolers, may also fall Article 422 for devices (440.3(c)).
Separation of means and accessibility
Proper separation methods are essential for safe maintenance of air conditioners.
Acceptable disconnect types:
Manual disconnect switches
Lockable circuit breakers
Cord and components (Only for plug-in equipment such as refrigerators, beverage coolers, or room air conditioning units) (440.13, 440.63)
Exceptions:
Over-current and ground fault protection for branch circuit
To protect against short circuits and ground faults:
Size OCPD (over-current protective device) In the beginning at 175% Compressor motor current rating (440.22)
If necessary for startup, increase up to 225% maximum Using the next crusher/fuse size available.
Sample size:
For 24A compressor:
Conductor size: 24A x 1.25 = 30 a → 10 og (Insulation 75°C)
OCD: 24A x 1.75 = 42A → Use a 40A breaker
If 40A trips: 24A x 2.25 = 54A → The next minimum size is 50A
Equipment with multiple compressors must display the maximum permissible rating for Obsessive-Compulsive Personality Disorder (OCPD) on plate.
Sizing connectors
Conductors should be sized based on 125% of rated load or branch circuit selection current (440.32). Use NEC Table 310.16 to find capacity.
Sample size:
For 18A motor:
Conductor: 18A x 1.25 = 22.5A → 12 AWG (rated 25A at 75°C)
OCD: 18A x 1.75 = 31.5A → 30 amp breaker
If necessary: 18A x 2.25 = 40.5A → 40 amp breaker (allowed per 240.4(g))
to Multiple compressors:
Room air conditioners (wired)
Room-connected air conditioning equipment (less than 40 amps, 250 volts, single phase) must follow Part VII of Article 440 (440.60):
It must be Factory installed AFCI Or leakage current detector (440.65)
Top Rope length:
Controls must be in place Within 6 feet from the ground or Within sight From cutting components
If used on common circuits:
Cable types and wiring methods for NEC 440
Wiring for HVAC and refrigeration systems should be selected to accommodate the following:
Branch circuit wiring:
thn/thn-2: Standard for internal duct installations
XHHW-2: Higher temperature rating; Common on wet surfaces or locations
mc cable: Often used for internal branch wiring; Available with copper or aluminum connectors
SE or USE-2: It is used to feed external condensing units from service panels; It must be resistant to sunlight and moisture
Channel systems:
Emergency medicine: Used indoors for roof-mounted raceways
For your mouth: Sealed flexible metal conduit to isolate vibrations and external equipment
LFNC: Non-metallic, flexible, air-tight conduit for similar applications with easy handling
PVC schedule 40/80: For external runs buried at the required burial depths
Overload protection and control circuits
Must include compressors Internal thermal overload protection Or use the listed external overload devices (440.52)
Control circuits must be (Class 2 or 3). I stay separate Of power cords unless rated (440.64)
When using shared enclosures, maintain physical separation or use included dividers to avoid interference and fire hazards.
Final thoughts
NEC Section 440 provides precise rules for wiring, protecting, and disconnecting sealed motors in heating, ventilation, and air conditioning (HVAC) and refrigeration systems. Main takeaways:
Always size the connectors in 125% of rated load
Size based obsessive compulsive disorder Start-up currentuntil 225% If necessary
Make sure to disconnect Visible, accessible, and lockable
Select cable types based on Temperature, humidity, flexibility and exposure of the site
Whether you are installing a commercial rooftop condenser, a residential split system, or a room air conditioning unit, following Section 440 ensures safe performance and code compliance for these high-demand electrical systems.
Nassau National Cable carries a wide range of cables for air conditioners.
