Talked to Steve at TRC, the manufacturer of the Surge Guard. They don?t want it mounted on its back parallel to gravity for the simple reason that if the relay failed mechanically, such as broken relay spring, it would fail closed, with no obvious indication of failure, and would provide no further protection.
In addition, these units loose their calibration over time. It is calibrated to open on high voltage of 132 VAC -/+ 3%, bringing it pretty close to the 126 VAC I typically see on each leg.
This unit also looks at neutral to ground, which should be zero, but in reality, can be a couple volts. If that exceeds 3 volts it will open. This should protect from a ?hot skin? condition in the coach, such as I have experienced on a couple occasions. These two instances of hot skin were when there was no grounding at the power source. It seems this unit would check for a good ground, but apparently it doesn?t. But in each case, I was using an adapter to use a 120 volt source as 240 wasn?t available. So, other than rechecking my ground bonding and internal coach terminal connections
The unit is sealed, and can?t be opened up and serviced. It is calibrated during manufacture, and can?t be re-calibrated after manufacturing.