Hi Jim,
WHERE are you placing MOVs? The only GOOD place for them is at the
service entrance, or in the panel where Neutral is bonded to Green. MOVs
should NEVER be used on branch circuits distant from the panel. When
MOVs are at a distance from the panel, the strike current raises the
voltage of the chassis by virtue of IR drop to the panel. When equipment
"protected" by MOVs at different locations, the strike will put each at
a different potential by virtue of the resistance and inductance of the
green wire at the two locations. When equipment at these different
locations is interconnected, the potential difference between them will
fry circuitry. It is VERY common for computers connected via Ethernet
to lose circuitry from a strike.
A good MOV at the service entrance will short strikes incoming on the AC
line, but additional current can be induced on branch circuit wiring. To
protect against this current frying interconnected equipment, SERIES
MODE protectors are required. They absorb the strike in a very large
inductor, then release it slowiy after the strike. This type of
protector is mfd by SurgeX, Brick Wall, and another mfr whose name I've
forgotten. SurgeX has been widely used in pro audio systems for nearly
20 years.
I'm using a Joslyn "whole house" MOV unit at my service entrance, and
SurgeX boxes at branch circuits in the shack, my XYL's office computer,
my entertainment center (TV, stereo), and for my XYL's
computer-controlled sewing machines and looms. That may be overkill --
the only stuff that is interconnected or bonded to ground locally is in
my shack and that entertainment center. The Joslyn is hanging across the
line through breakers within a disconnect panel.
73, Jim K9YC
On 9/21/2018 12:23 PM, Jim Thomson wrote:
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 ?
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 ?
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.
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.
Tnx... Jim VE7RF
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