Re: Well, I know what's wrong - My brand new NST fried!!

["Gomez ADDams" <gomez-at-netherworld-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

on that fateful day 8/23/00 8:11 AM, Tesla list uttered:

> Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
> 
> Hi Garry,
> 
> A MOV is a Metal Oxide Varistor.

 I'd like to throw my $0.02 in concerning MOV's.

 I have done some work in "power quality", and in that industry MOV's are
rather notorious.

 Every time an MOV "fires" (turns on, shorting out a transient), it loses a
small but non-zero amount of its active area.  Active area is the part of
the working material between the two contact pads.  As the active area goes
down, the current density per unit area goes up with each successive firing.
Eventually, the thing goes bang.

 Essentially, MOV's have a finite but unpredictable life span, depending on
the energy contained in each transient diverted, and the number of
transients diverted.

 In the case of MOV's being used for power protection (they are the active
switching elements in nearly all "surge protectors"), an MOV can operate for
many years, or only a few months before it fails.  When it fails, it will
fail catastrophically.  Ever failed "surge protector" I have ever seen had a
pair of wires and a smoking hole where the MOV(s) used to be.

 This is why fast-blow fuses in "surge protector" outlet strips are a must!
When an MOV finally fails, it can pull huge amounts of current.  There are
several hundred documented cases where surge protection outlet strips were
the cause of house fires.

 Now in the case of NST protection networks, it's probably cheaper to
replace an MOV string every few years (as, if, and when necessary) than to
keep buying new NST's!  And not too many Tesla coil power supplies are
turned on all the time.  Therefore, I don't think we coilers need to worry
too much about our NST protection networks burning down our houses.

 But all this goes to illustrate why, in my not so humble opinion, you
should never plug a Tesla coil of any size into a "surge protected" or
"filtered" outlet strip.  If you're concerned about HV transients or RF
noise getting back into the power lines, it's far easier to build your own
filter network using large inductors and capacitors that will never, ever
fail due to wearing out.

 It also shows why, again IMNSHO, that if you're going to use inexpensive
"surge protectors" you should consider buying units with a metal case, or
find products which do not use MOV's at all.

- Gomez Addams (Bill Lemieux)

PS: if anyone wants a recommendation for a non-MOV "bomb proof" power line
surge filter product, email me- I'm not connected with the company, I'm just
a true believer.

....................................
If "all the world's a stage", I want
better lighting and costumes!