My Rinnai R94LSe has two electrical connectors on the bottom, one is a ~1" diameter white threaded plastic connector for the remote, the other is a ~1/2" black rubber grommet - I assume for the 120VAC.

The black grommet will not provide any protection from the AC line pulling out and causing damage or shock. I though the hole in the chassis should be connected to with a 1/2" flex conduit, or at least a romex clamp to hold the cable tight. BUT its not a 1/2" connector - its just shy - I was unable to get a 1/2" connector in the hole.

How have you seen this done? Thanks for your advice!