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
WB8WKU
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