Article 440, Part VII provides the requirements for room air conditioners. These are typically installed in residential applications, but they show up in other applications as well. For example, large retail outlets may have a small locked room in the back store room for storing candy bars or other products that need to be stored in a relatively cool area. Where it is installed isn’t its defining characteristic. Part VII repeatedly uses the phrase “cord and plug connected” or “cord and attachment plug connected”.
A room air conditioner is considered a single-motor unit for the purpose of determining its branch circuit requirements if four conditions are met [440.62(A)]:
- It’s cord and attachment plug connected.
- Its rating is not more than 40A and 250V single-phase.
- Its nameplate shows the total rated load current.
- The rating of the branch circuit short-circuit and ground-fault protective device doesn’t exceed the ampacity of the branch-circuit conductors or the rating of the receptacle (whichever is less).
At first glance, No. 4 doesn’t seem to fit. What does the breaker rating have to do with whether the air conditioner is a single motor unit? The answer is this refers to the value shown on the air conditioner nameplate. For example, if it says 30A on the nameplate then you can’t use a 20A circuit to supply it. You can’t use a 30A circuit, either. Why is that? Because (where no other loads are supplied), that value can’t exceed 80% of the current rating of the branch circuit [440.62(B)].
What if lighting units or receptacles are also supplied? What happens to that 80% figure? In this case, it drops to 50% [440.62(C)]. But if you have an interlocked system where you can either run the air conditioner or power those other loads, then it goes back up to 50%. Take that candy bar room. Maybe you don’t want cold air blowing on employees who are moving candy bars in or out of that room or in there doing an inventory count. So, the air conditioner will run only when the light is off.
It would seem obvious that the plug and receptacle can be used as a disconnecting means. Yes, but only if two conditions are met [440.63]:
- The unit’s manual controls are readily accessible.
- There’s also an approved manually operable disconnecting means in a readily accessible location within sight of the unit.
You don’t want to unplug something when it’s running; that is not a safe way to do it because of the arc generated. You shut the equipment off, first. This goes for anything with a motor, such as a refrigerator or vacuum cleaner. Before someone unplugs that room air conditioner, they should shut it off. Thus these two requirements.
Flexible cords are often provided with these units. Such a cord can’t be longer than 10 ft for a 120V unit and not longer than 6ft for a 208V or 240V unit [440.64]. This requirement can pose installation challenges. Attempting to solve this problem by using an extension cord clearly violates the intention of this rule. You can solve it by extending the permanently installed wiring closer to the unit (add conductors and a receptacle to the existing branch circuit), running a new branch circuit specifically for this unit, or moving the unit closer to where it needs to plug in.
The units come with the correct cord length. The cords are also protected with one of three devices, installed at the factory [440.65]. Those are leakage-current detector-interrupter (LCDI), heat detecting circuit interrupter (HDCI), or an AFCI. If you’re tasked to do any work related to a room air conditioner, make sure one of these devices is present and hasn’t been tampered with.
