|NEC Article 440 - Air Conditioning and Refrigerating Equipment
|By Mike Holt for EC&M Magazine
Knowledge of Article 440 requirements is increasingly
in hot demand.
Long-time EC&M reader Joe Territo, president of
Territo Electric in Ocoee, FL, knows the importance of Article 440 and its
growing role in facilities. A Territo client operates a multi-story building
that exists for one purpose: to make and supply chilled water to nearby
customers. Chilled water buildings have been popping up in cities across the
country. And they have something in common with data centers, clinical labs,
temperature-controlled industrial enclosures, and probably your own office-they
come under Article 440, because they use electrically driven air-conditioning
and refrigeration equipment that has a hermetic refrigerant
What is a hermetic refrigerant motor-compressor? It's a
combination consisting of a compressor and motor enclosed in the same housing.
These have no external shaft or shaft seals, and the motor operates in the
Article 440 does not cover such household appliances as room
air-conditioners, household refrigerators and freezers, drinking water coolers,
or beverage dispensing machines, because these are appliances and must comply
with Article 422.
Article 440 requires you to
locate the disconnecting means within sight of, and readily accessible from, the
air-conditioning or refrigerating equipment (Figure 440-2). "Within sight" means
visible from, and not more than 50 ft from, each other [Article 100] (Figure
440-4). You can install the disconnecting means on or within the
air-conditioning or refrigerating equipment-but not on the access panels (Figure
This requirement has two exceptions:
You can lock the
switch open if the equipment is essential to an industrial process and the
installation meets certain requirements.
Where a plug and receptacle serve
as the disconnecting means, they must be accessible. But they need not be
The requirements for
protecting the branch-circuit conductors, control apparatus, and circuits
supplying hermetic refrigerant motor-compressors against short circuits and
ground faults are in [440.22].
The size and type of the short-circuit and
ground-fault protection device for air-conditioning and refrigeration equipment
are often marked on the equipment nameplate. The manufacturer calculates these
ratings per [440.22] and [440.32] (Figure 440-5).
If the equipment
nameplate specifies "Maximum Fuse Size," use a one-time or dual-element fuse. If
the nameplate specifies "HACR Circuit Breaker," use an HACR-rated circuit
Short-circuit and ground-fault protection cannot
exceed the nameplate ratings. If the equipment does not have a nameplate
specifying the size and type of protection device, how do you size those
devices? That depends on whether you are sizing for multiple motors or a single
Rating for Equipment. Where the equipment incorporates more than
one hermetic refrigerant motor-compressor, or a hermetic refrigerant
motor-compressor and other motors or other loads, size the equipment
short-circuit and ground-fault protection with the "largest load" method. The
rating of the branch-circuit short-circuit and ground-fault protective device
cannot exceed the largest motor-compressor short-circuit ground-fault protection
device plus the sum of the rated-load currents of the other
Size the branch-circuit conductors at 125 percent of the
larger motor-compressor current plus the sum of the rated-load currents of the
other compressors [440.33].
One Motor-Compressor. The short-circuit and
ground-fault protection device for motor-compressor conductors must be capable
of carrying the starting current of the motor. Also, the protection device
cannot exceed 175 percent of the equipment load current rating.
protection device sized at 175 percent is not capable of carrying the starting
current of the motor-compressor, you can use the next larger protection device
if it does not exceed 225 percent of the motor-compressor current
Test your knowledge with this question: What size conductor and
protection must you have for a 24A motor-compressor on a 240V circuit (Figure
10 AWG, 40A
10 AWG, 60A
A or B
none of these
Answer: (a) 10 AWG, 40A protection.
Here's how we arrive at that
Step 1: Size the branch-circuit conductor [Table 310.16 and
24A x 1.25 = 30A, 10 AWG, rated 30A at 60°C [110.14(C) and Table
Step 2: Size the branch-circuit protection [240.6(A) and
24A x 1.75 = 42A, next size down protection = 40A.
a 40A protection device is not capable of carrying the starting current, you can
size the protection device up to 225 percent of the equipment load current
rating (24A x 2.25 = 54A, next size down 50A).
Size these branch-circuit conductors no smaller than the spec on
the equipment nameplate. If the equipment does not have a nameplate specifying
the branch-circuit conductors, size the conductors per [440.32] (Figure
One Motor-Compressor. Suppose your equipment is not marked with
minimum circuit ampacity. For each single motor compressor, use a branch-circuit
conductor ampacity not less than 125 percent of the motor-compressor current.
Protect branch-circuit conductors against short circuits and ground faults
between 175 percent and 225 percent of the rated-load current. See
Several Motor-Compressors. Conductors that supply several
motor-compressors must have an ampacity of not less than 125 percent of the
highest-rated motor-compressor current of the group plus the sum of the
rated-load currents of the other compressors. Protect these conductors against
short circuits and ground faults per [440.22(B)(1)].
The rules in Part VII of Article 440 apply to window or
in-wall type room air-conditioner units that incorporate a hermetic refrigerant
motor-compressor rated not over 40A, 250V, 1Ø. These units are common in homes,
hotels, and mobile shelters such as construction trailers. But, you'll see them
in many other applications as well.
When calculating branch-circuit
requirements, you can consider a room air-conditioner to be a single motor unit
only if the installation meets the four conditions listed in [440.62(A)]. You
must make three branch-circuit determinations:
Conductor and Protection
Size. Branch-circuit conductors for a cord-and-plug-connected room
air-conditioner rated not over 40A at 250V must have an ampacity of not less
than 125 percent of the rated-load currents [440.32].
Maximum Load on
Circuit. Where the room air-conditioner is the only load on a circuit, the
marked rating of the air-conditioner cannot exceed 80 percent of the rating of
the circuit [210.23(A)].
Other Loads on Circuit. The total rating of a
cord-and-attachment-plug-connected room air-conditioner cannot exceed 50 percent
of the rating of a branch-circuit where lighting outlets, other appliances, or
general-use receptacles are also supplied [210.23(B)].
Air-Conditioning Disconnecting Means
The supply cord for room
air-conditioning equipment cannot be longer than 10 ft for 120V units or 6 ft
for equipment rated 208 through 240V. An attachment plug and receptacle can
serve as the disconnecting means for a room air-conditioner, provided (Figure
The manual controls on the room air-conditioner are readily
accessible and within 6 ft of the floor, or
An approved manually operable
switch is in a readily accessible location within sight from the room
Unless you have special certification, your work on
refrigerant systems does not include breaking refrigerant seals or working with
the refrigerant itself. But it does include properly applying Article 440 to
protect circuits and ensure reliable operation of the equipment. Whether you are
keeping beverages cold at your local convenience store or keeping tissues alive
at a medical clinic, your knowledge of Article 440 will allow you to do the job
Copyright © 2002 Mike Holt Enterprises,Inc.