Date: Thu, 23 Jan 2014 22:31:53 -0800
From: Jim Brown <jim@audiosystemsgroup.com>
To: amps@contesting.com
Subject: Re: [Amps] MOVs
On 1/23/2014 7:18 AM, Paul Baldock wrote:
> If the amp is running off 240V where in the USA this is symmetrical
> about ground and then the MOV is placed between the two phases, it
> seems to me that there would not be a surge current to ground.
Right. The problem comes when you take the MOV to the ground.
73, Jim K9YC
## On whole house protectors, they use a pair of huge, FUSED
130 V rated movs.... wired from each hot side to the neutral...which of
course is also grounded. So you end up with 2 x movs, nose to tail, in series
across the 240 V line..with the junction point bonded to neutral + ground.
## telcos use the same deal on 240 v –120v sites..like cell sites. In bigger
offices,
where 208 + 120 vac 3 phase power is used, 3 x movs are used...and each is
wired
from each hot...to neutral. neutral is grounded at the service entrance.
The fuse is
between each hot leg and mov. On the output side of each fuse is the 120 vac
coil
for a 4PDT relay..wired from fuse output ..to neutral. A 120 vac neon is
also wired from
output side of each fuse..to neutral. In normal operation, the neon is
lit..and the 4PDT relay
is operated at all times 24-7. IF the fuse ever blows open, the neon goes
out..and the relay
also drops out..... which brings in an alarm.
## In the case of 120 vac ham gear, you might be able to wire a FUSED mov
between the 120 vac
hot leg and neutral. In the case of 240 vac ham gear, You could wire a
SINGLE FUSED 250 vac rated
MOV between the 2 x hot legs. You could also wire 130 v rated movs from each
hot leg to neutral...
then you are still protected from spikes on either or both sides of the hot
legs. Then nothing is getting
conducted back to ground...except back at the main 200A panel..where the
neutral is bonded to the ground.
## On paper, it should work. Ideally the best way would be to use the whole
house protector scheme
right at the main 200A panel. Then the entire 200A panel is protected from
transients coming down the
drop wire into the home. It should also kill transients + spikes from any
equipment on any branch lines...
like electric motors etc. But then again, the electric motor, etc could be a
loooong way from the main panel
movs.
## On paper, using MOVS at the 200A main panel AND the equipment, line to
neutral and not line to ground at the
equipment end... should work. IF movs are not fused..you are asking for
trouble. Real simple to fuse em..plus add
a neon or led on the output side of the fuse to serve as a visual indicator
that the fuse is functional..... which of course
also means the mov is functional.
## I will defer to Jim Brown as to his thoughts of using movs wired from hot
to neutral at the equipment end of things.
Another thought is to wire all ham gear for 240 vac use if possible..including
xcvrs etc..but that is not always possible.
Jim VE7RF
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