The user manual says to use a nema 6-15R with a 15A two pole Circuit breaker(240V). But my existing setup is a nema 6-20R with a 20A two pole CB(240V). I realize a 6-15P plug will fit into a 6-20R receptacle but I am worried about over-loading the new A/C. Does anyone know if this new A/C has built in "Overcurrent protection"? Also this A/C is the new "Dual inverter technology". This unit draws 10.5/11.6 amps.I read the NEC article Table 210.21(B)(2) that says the maximum load on a given circuit is 80% of the receptacle rating and circuit rating. The maximum load on a 20A OCPD is 16A. Is this OK to do? I don't want to damage my A/C or house?LG-LW2217IVSM ]3
This unit requires a 15A breaker
The manual for this particular machine specifically calls out a 15A circuit breaker. That is the final word on the subject; NEC 110.3b requires you obey the labeling and instructions. (the reason is that the UL listing is contingent on installation according to the labeling and instructions; UL hasn't tested this unit on a 20A breaker and does not vouch for its reliability.)
Which means you must change the receptacle also
Since you must install a 15A circuit breaker, that will also necessitate installing a NEMA 6-15R receptacle, since you can't have a 20A receptacle on a 15A circuit.
However, the wire in the walls can remain the same. Presumably it is 12 AWG (or possibly 10 AWG; too-large wire is always allowed).
In some point in the future, when no longer using an air conditioner calling out a 15A breaker, you could roll it forward to a 20A breaker, since the wire is adequate. Note that a 20A circuit can have 15A receptacles, but only if there are 2 or more of them. (a single receptacle is for an appliance on a dedicated circuit; breakers must match there). I note that nothing in the documentation of this appliance calls for a dedicated circuit, so a dual NEMA 6-15 receptacle would be perfectly acceptable with this A/C, and possibly cheaper than a solo, and that dual receptacle would be acceptable on a 20A breaker (if not for this A/C unit's restriction).
NEC Code couldn't care less, except for 110.3(b)
If it hadn't been for the labeling and instructions, Code would have been fine with this. The whole point of the 20A/15A exception in 210.21(B)(3) is that you're allowed to load up 20A circuits with the common 15A receptacles, which take loads far smaller than 15A -- cell phone chargers, laptops, Roku boxes, clocks, LED lights, nightlights, etc. The electrical system is built constant-voltage, which means each device is responsible for its own current draw and must self-regulate.
That is why NEMA 5-20 and 6-20 receptacles have T-shaped pins - to allow NEMA x-15 plugs to fit. As discussed in 210.21(B)(3), this is the only exception -- the 40/50A quasi-exception is because NEMA refuses to define a standard for a 40A plug/socket... so 40A circuits are forced to use 50A receptacles.
The cast of characters. Ms. Yikes, Ms. Winky, Ms. Nope, and Ms. Grumpy. They are, after all, female.
The basic answer is: You should be OK.
You are looking at the numbers "backwards". A 20A receptacle/breaker/etc. (assuming everything is installed correctly) can safely supply up to 20A total, and up to 16A continuous load. A 15A receptacle/breaker/etc. can safely supply up to 15A total, and up to 12A continuous load.
While generally speaking an appliance and the circuit should be carefully matched, there is an exception for 15A & 20A circuits. This is actually in two ways:
- A 20A circuit can have 15A receptacles. That's plural - you can't have a 20A circuit that has exactly one 15A receptacle. This allows you to have multiple devices on the circuit that together pull more than 15A (or more than 12A continuous) without having nuisance trips, while still providing protection at a reasonable level - if there is a current draw > 20A.
- 20A receptacles are designed to accept both 15A and 20A plugs. This allows you to install, for example, 20A receptacles on a 20A circuit in a workshop in order to use heavy-duty power tools that actually need 20A circuits and use the same receptacles for much smaller devices (15A tools on down to < 1A cell phone chargers, etc.)
These issues are far more common with 120V circuits, but apply to 240V circuits (your situation) as well.
This is all by design. End result: a 15A device can be plugged in to a 20A receptacle. In normal usage it will not overload the circuit - in fact it will be well under the capacity of the circuit, which is perfectly fine. If there is a real overload situation, it will likely be far greater than 20A and will trip the breaker. No different from plugging a cell phone charger that uses a small fraction of 1A into a 15A circuit - the device (unless there is a failure) will use only the electricity it needs.
This is not the case with larger - e.g., 30A, 40A, 50A circuits. Each of those has a particular receptacle designed to match exactly (there are some small exceptions, but not like the "universal" 15A/20A rules).
It is generally OK* to plug a lower-rated appliance into a higher-rated socket. The appliance will not draw more power than necessary.
Your existing 20A socket should have a T-shaped prong so that you can plug in either a 15A or 20A plug.
No extra breaker is needed.
*There are possible problems where a very big difference exists, e.g. a 15A device into a 50A or larger socket, as the upstream breaker might not trip if there's a fault in the appliance. This isn't a concern on a 20A circuit.