[Amps] 130 V MOV placement ??

[Jim Brown]

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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