Long-time EC&M reader Joe Territo, president of Territo Electric in Ocoee, Fla., knows the importance of the requirements of Art. 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 fall under Art. 440, because they use electrically driven air conditioning and refrigeration equipment that has a hermetic refrigerant motor-compressor.
A hermetic refrigerant motor-compressor is a combination unit that consists of a compressor and motor enclosed in the same housing. These devices have no external shaft or shaft seals, and the motor operates in the refrigerant.
The requirements of Art. 440 don’t cover household appliances like room air conditioners, household refrigerators and freezers, drinking water coolers, or beverage dispensing machines. These products are defined as appliances, and they must comply with the requirements of Art. 422.
To keep you from losing your cool on these projects let’s take a closer look at the actual requirements of this article.
Disconnecting means. Art. 440 requires you to locate the disconnecting means within sight of, and readily accessible from, the air conditioning or refrigerating equipment. “Within sight” means visible from and not more than 50 feet from each other [Art. 100]. You can install the disconnecting means on or within the air conditioning or refrigerating equipment—but not on the access panels (Fig. 1).
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 readily accessible.
Circuit protectionThe requirements for protecting the branch-circuit conductors, control apparatus, and circuits that supply hermetic refrigerant motor-compressors against short circuits and ground faults are noted 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 (Fig. 2).
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 breaker [110.3(B)].
Short-circuit and ground-fault protection can’t exceed the nameplate ratings. If the equipment doesn’t have a nameplate that specifies the size and type of protection device, how do you size those devices? That depends on whether you’re sizing for multiple motors or a single motor.
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 can’t exceed the largest motor-compressor short-circuit ground-fault protection device plus the sum of the rated-load currents of the other compressors.
Size the branch-circuit conductors at 125% 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. The protection device also can’t exceed 175% of the equipment load current rating.
If the protection device sized at 175% isn’t capable of carrying the starting current of the motor-compressor, you can use the next larger protection device if it doesn’t exceed 225% of the motor-compressor current rating.
Test your knowledge with this question: What size conductor and protection device must you use for a 24A motor-compressor on a 240V circuit (Fig. 3)
Step 1: Size the branch-circuit conductor per Table 310.16 and 440.32.
24A x 1.25 = 30A
Per 110.14(C)(1)(a) and Table 310.16, you would select a 10 AWG conductor, rated 30A at 60°C.
Step 2: Size the branch-circuit protection device per 240.6(A) and 440.22(A).
24A x 1.75 = 42A
Selecting the next size down protection device yields a 40A device.
If a 40A protection device isn’t capable of carrying the starting current, you can size the protection device up to 225% of the equipment load current rating (24A x 2.25 = 54A, next size down 50A).
Conductor sizing. Size these branch-circuit conductors no smaller than the spec on the equipment nameplate. If the equipment doesn’t have a nameplate that specifies the branch-circuit conductors, size the conductors per 440.32.
One motor compressor. Suppose your equipment isn’t marked with minimum circuit ampacity. For each single motor compressor, use a branch-circuit conductor ampacity not less than 125% of the motor-compressor current. Protect branch-circuit conductors against short circuits and ground faults between 175% and 225% of the rated-load current. See 440.22(A).
Several motor compressors. Conductors that supply several motor-compressors must have an ampacity of not less than 125% 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).
Room air conditioners. The rules in Part VII of Art. 440 apply to window or in-wall type room air conditioner units that incorporate a hermetic refrigerant motor-compressor rated not more than 40A and 250V (single-phase). 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 more than 40A at 250V must have an ampacity of not less than 125% 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 can’t exceed 80% 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 can’t exceed 50% of the rating of a branch-circuit where lighting outlets, other appliances, or general-use receptacles are also supplied [210.23(B)].
The supply cord for room air conditioning equipment can’t be longer than 10 ft for 120V units or 6 ft for equipment rated 208 through 240V (440.64). An attachment plug and receptacle can serve as the disconnecting means for a room air conditioner, provided:
- 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 of the room air conditioner.
Unless you have special certification, your work on refrigerant systems doesn’t include breaking refrigerant seals or working with the refrigerant itself. But it does include properly applying the requirements of Art. 440 to protect circuits and ensure reliable operation of the equipment. Whether you’re helping keep beverages cold at your local convenience store or keeping tissue alive at a medical clinic, your knowledge of Art. 440 will keep your customer from losing its cool.