[Amps] 130 V MOV placement ??

[Manfred Mornhinweg]

Jim,

> IF  using a 130 V rated   MOV,   where  does it get wired ?   Do you
> wire between  120 vac  and neutral.... or  120 vac and chassis of
> equipment in  question ?

Between 120VAC phase and neutral. NOT to the chassis!

> IF  a spike  / transient /  glitch  etc  occurs.and  MOV
> conducts..which  path do you want the fault current to flow through,
> the ground wire or the  neutral ?

You want it to flow through the neutral line, so that the chassis of 
your equipment does NOT get a dangerous voltage on it. If a high fault 
current was injected into the chassis, all the inductance and resistance 
of the ground wire might cause enough voltage drop to become dangerous.

> The only place the  neutral and ground are bonded together is at the
> main 200A panel.   On my 100 A  sub panel, the neutral + ground are
> NOT bonded,  per the electrical code.

That's fine. And there should be a GOOD, real earth connection there.

That bonding matter is controversial, though. In my country the law 
requires that the neutral and protective earth lines are NOT bonded, but 
instead each has its own earth connection. The neutral at the 
distribution point (pole pig), the protective earth right at the house.

Each of the two systems has advantages and disadvantages.

> Either way, the  MOV  is fused, so if it does fail  shorted... the
> fuse opens up.   Also  I use a neon  /  led  wired between output of
> fuse..which is also the input to the MOV...and neutral. In normal
> operation, the  neon / led is illuminated.    IF fuse opens  up, the
> neon / led  goes  out.... telling me the MOV is doa.

It would be better to use just the main fuse of the equipment, so that a 
dead, shorted MOV blows the main fuse, instead of allowing the equipment 
to keep powered and eating the overvoltage that blew the MOV!

If just the MOV is fused, the sequence is this: BIG surge starts - MOV 
clamps the surge - MOV fails shorted - MOV fuse blows - now unclamped 
surge goes on to equipment - equipment blows up. Instead when using just 
the main fuse, the sequence is: BIG surge starts - MOV clamps the surge 
- MOV fails shorted - main fuse blows - equipment loses power but 
remains unharmed except for MOV and fuse.

MOVs are intentionally designed to fail in short circuit, TO PROTECT 
EQUIPMENT, not to be disconnected by fuses, defeating that protective 
function!

Manfred

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