In message
<64D32EE8B9CBDD44963ACB076A5F6ABB0266533F@Mailbox-Tech.lecotech.local>,
dated Mon, 9 Sep 2013, "Kunde, Brian" <brian_ku...@lecotc.com> writes:
What are the safety considerations using gas tubes on the AC mains? Do
you have to fuse them or are they not likely to fail shorted?
Not likely, but in theory anything with metal electrodes can arc over,
and the arc has negative resistance. Fuses may not help, because they
can arc over as well.
Can you use them between line and PE? Do you have to use multiple parts
in series? I often see them in series with MOVs in a “T”
configuration to protect against line to line and line to PE surges.
Opinions tend to differ on this. The text in IEC 60950-1 was quite
controversial.
A few year back we had a product that had several surge suppression
circuits located on different PC boards within (some assemblies were
very expensive and we wanted to protect them). Well, at our customer
site they experienced some kind of huge surge, transient or overvoltage
(we do not know what exactly happened).
That's a pity. It might have paid to hire an expert to try to find a
cause.
Of all the equipment that was on-site including many of our competitors
equipment, only our instrument was damaged. Our surge suppressors were
blown up, charred, and/or vaporized.
Surges can be extremely selective like that.
The warranty repair cost was $10,000US but the hit to our reputation
was probably worst. We believed that our equipment probably protected
all the other equipment on-site but it is hard to get your customers to
believe you. So now we want to better control our surge protection and
if we see a huge surge we hope it to destroy something much less
expensive to replace or at least minimize the damage.
Do you know about the collection of science and lore on protection in
the ITU-T series K publications? You can get these from:
http://www.itu.int/rec/T-REC-K/e
and I think they are free, but there may be a limit on how many one
person can download.
What we are currently thinking is to use over the counter Surge
Suppressor modules, but they are only good to about 3KV – 4KV. Then
we thought we would add a spark-gap in the board that would only kick
in if our surge suppressors failed. Maybe we can add some very high
voltage Gas Tubes also or instead of the spark-gap. I’m not sure
what more we can do. Many of the circuits/assemblies we are trying to
protect are buy/sell components where we do not control spacings.
I suggest you look at the K series publications before making any
decision.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
If dictionaries were correct, we would only need one, because they would all
give the same information.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
-
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