Date   : Wed, 06 Mar 1985008:13:00-EST
From   : jrv@mitre-bedford.ARPA
Subject: MOV transient protectors

I can't see why more than one MOV would be necessary to protect the AC
power (hot to neutral), because I can't see anything that would drive
a transient from hot to ground or ground to neutral.  Big, inductive loads
switching on and off (motors, relays) create transients from hot to
neutral.  Any sources outside the building can only drive transients from
hot to both ground and neutral, because ground and neutral are connected
at the circuit breaker box.  Assuming the building is wired with grounded
outlets, all three wires run in parallel from the breaker box to the outlet,
so even VHF radiation can't drive a big differential mode signal.  The only
source I could think of for a big signal from ground to something else is
a lightning strike to just one wire - and I wouldn't expect any MOV to
handle that!                - Jim Van Zandt