National Electrical Code Top Ten Tips: Article 440 -- Air Conditioning and Refrigeration Equipment
by Mark Lamendola
Based on the 2020 NEC
Please note, we do quote from copyrighted material. While the NFPA
does allow such quotes, it does so only for the purposes of education
regarding the National Electrical Code. This article is not a substitute
for the NEC.
These are the 10 NEC Article 440 items we deem most important, based
on the pervasiveness of confusion and the potential costs of same.
- Article 430 also applies. You cannot apply Article 440 without
also applying Article 430 [440.3]. This also means that if you are going to work on air conditionnig and refrigeration equipment, you need things like a rotation tester, a vibration tester, and an insulation resistance tester. You also need a torque wrench so that you correctly tighten all mounting hardware; a mistake here can shorten motor life dramatically.
- This Article applies to air conditioning and refrigeration
equipment that has a hermetic motor. For all other air
conditioning and refrigeration equipment, refer to Article 422, 424, or 430 as appropriate [440.3]. A hermetic motor is one that is (hermetically) sealed into the system. It's actually in the refrigerant.
- Determine the ampacity and rating of equipment per 440.6(A) and
440.6(B). For ampacity, be sure to adjust for voltage drop. Going one conductor size up can save thousands of dollars of electricity over the life of the equipment.
- When performing calculations for multi-motor installations
(meaning you will comply with 430.24, 420.53, and 430.62), you have
to consider one motor to be the one with the highest rated load
current. That motor is going to be whichever motor is the largest.
If your two largest motors are the same size, pick either one
- Air conditioning and refrigeration system motors are considered
a single machine, even if the motors are remotely located from each
- When sizing the disconnects for air conditioning or
refrigeration system equipment, different methods appl, depending
on the type of load. The load type may be a single hermetic motor
only, combination loads, or a small motor load [440.12(A),
440.12(B), and 440.12(C).]
- The rules for disconnects in 440.11 apply to every disconnecting
means that is in the motor-compressor circuit between the point of
attachment of the feeder and the point of connection at the motor
[440.12(D)]. When mounting a disconnect, take into account where the operators must stand. Avoid mounting in such a way that the operator is in the blast path if a blast inside the disconnect blows the door open. This means the operator will not stand in front of the disconnect to operate it, but to one side. These are meant to be operated with the left hand, under the theory that most people are right-handed and in a worst-case scenario it's better to lose your left hand than your right hand. Keep all of this in mind when deciding where to mount a disconnect.
- Size your short-circuit and ground-fault protective devices such
that they are capable of carrying the motor starting current
[440.22(A) and 440.22(B)], but don't use a protective device that
exceeds the manufacturer's values [440.22(C)]. If that protective device won't permit starting, the problem isn't the protective device. There is something wrong. First, check the supply voltage by starting at the motor power input terminals and working your way back if you don't find power there. It is possible you simply need to reset or (depending on type) replace the motor overload protective device(s). If the power checks out, remove the motor and turn the shaft by hand. Listen carefully for a scraping noise (bearings). If the shaft won't turn, replace the motor. If the shaft turns freely and silently, procede to the next phase of troubleshooting.
- When sizing the branch circuit conductors for air conditioning
or refrigeration system equipment, different methods apply,
depending on the type of load. The load type may be a single
hermetic motor only [440.32] or combination loads [440.34 and
- You must provide separate overload protection for the
motor [440.52(A)] and overcurrent protection for the
conductors [440.52(B)]. This is the same principle we find in Article 430, but with some amendment of the particulars.