MOV's should never tie to the safety ground lead or any
ground lead outside of an entrance panel. They can have very
large fault currents and, if sized to close to the power
line voltage, can go into thermal runaway.
They can tie back to a suitably sized neutral lead, but we
all know the neutral cannot be grounded at the equipment.
Since the clamping voltage is pretty high anyway, you might
as well size for some margin. I'd use MOV's rated at 140-150
volts continuous AC if I was sure the line would never go
over 120.... if I used MOV's.
73 Tom
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