Can I plug my new LG-LW2217IVSM A/C nema 6-15P into a 6-20R with a 20A-240V CB?
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 &amp; 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 &lt; 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).