Re: NST Filter

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Michael Rhodes by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rhodes-at-fnrf.science.cmu.ac.th>

A MOV (Metal Oxide Varistor) has three parts -- a piece of metal oxide
material in the middle, joined to the power and grounding line by two
semiconductors. These semiconductors have a variable resistance,
dependent on voltage. When voltage is below a certain level, the
electrons in the semiconductors flow in such a way as to create a
very high resistance.When the voltage exceeds that level, the electrons
behave differently, creating a much lower resistance. When the voltage
is correct, a MOV does nothing. When voltage exceeds the MOV's rated
threshold it conducts, behaving essentially as a short circuit.  In other
words
clamping any spikes.  Switching times are very fast, nanoseconds.  If
the overvoltage exceeds the average power rating of the MOV it will
often 'pop', that is explode and open circuit and its protection is lost so
it is a good idea to have more then one in parallel.  Best configuration is
MOV from hot-neutral, hot-ground, and neutral-ground to cover any
common mode spikes/surges (if applied on the mains side of the NST).

--Michael

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, June 08, 2001 5:43 AM
Subject: NST Filter


> Original poster: "Jason Petrou by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jasonp-at-btinternet-dot-com>
>
> Hi Terry,
> I am usng an NST for the first time (kind like and upgrade from MOTs) and
> have got a couple of questions about your filter which i will use (of
> course). Firstly is it suitible for a 10/100? secondly any idea whaere I
> could get the components in the UK? thirdly, what are MOVs and what do
they
> do, and how do they do it?
>
> Thanks,
> Jason
>
>
>