I use the TRC, now Southwire, 50 amp external plug in unit. I found a stainless steel shackle pad lock with a shackle large enough to go around the power cord. I use that with a chain around the power post to discourage theft. Seems to work well on both 50 and 30 amp power poles. It samples the incoming power for about 2 minutes before closing the internal relay to allow power into the coach. Actively shuts the power off if the incoming power goes out of range or looses neutral.