[Amps] MOVs

Gene May gene-may at hotmail.com
Wed Jan 9 18:07:39 EST 2013

Vic K2VCO and all,
You are correct that the technique to be used in the USA -- two VA130 MOVs each connected from one of the hot wires to ground -- wouldn't work with no ground.  I have used the following system for years in northern Virginia where I live, without either any problems with the electric system or damage to any gear from lightning pulses:  (1) two VA130 LA20's connected as above and a VA250LA40 across the two hot 240 VAC leads, and (2) .001 or .01 uF caps rated at least a kilovolt each in parallel with each of the MOVs.  Its best to use caps designed to go across commercial mains.  We have common Spring thunderstorms in this area that are powerful enough to cause power outages.  I've experienced no direct hits but some strikes closer than a half mile, so my experience is some measure of performance and protection.
The VA250LA40 is somewhat duplicative, but provides some extra protection against differential-mode pulses, and it has never blown.  I would imagine that it would work fine in your intended use.  If you can't find these, the manufacturers' data sheets I've seen indicate that connecting VA130's in series will work fine.  Keep the leads short in any case to reduce inductance and delay.
These things are cheap, and often available from usual surplus dealers (Fair Radio, Nebraska, ...)  I regard them as very cheap and very good insurance, and they also seem to do a nice job of removing some of the normal man-made lower-power pulses that are generated by motors, etc.
There are a number of manufacturers of these devices, and they post their data sheets and application notes on the web.  I've used Littelfuse partly because they have so much good info application info on the web, and they are widely distributed.  Wikipedia has a useful piece on MOVs also.
Before I plugged in anything in Israel that was designed for use in the USA, I would check out the equipment's internal grounding to be sure that it is still safe for use in those circumstances.  You don't want either a "hot" chassis or a short to ground somewhere.  It is also likely that a US plug won't fit in Israel.
I've worked for a company in the US that made electrical devices for foreign use, and we ALWAYS cut off the "US" plugs from what we shipped overseas.  Other countries vary considerably in how they use and connect ground, and we wanted to insure that our customers figured out their own local, safe way to connect. 
Gene May


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