In a previous life I spent almost four years as Senior
Applications Engineer for PolyPhaser, a manufacturer
of surge suppression products. Poly primarily uses MOV's.
>From a more previous life as an evaluation engineer for a
major cable television operator (it don't get bought 'till I say
it can be bought), I evaluated offerings from many of the
players in the surge suppression field.
IMHO, MOV's and SAD's do the job. From the aspect of
protecting from lightning induced surges (as opposed to
power line glitches), I believe MOV's are the way to go.
The SAD cannot handle the power that the MOV can.
Therefore, a multitude of SAD's are employed in a series-
parallel matrix. The problem is they much be matched in
capability to 1 or 2 percent. Very costly, but this is the way
Transtector does it. Anyway, in my mind, this matrix is
susceptible to the domino effect when one SAD fails and
over time drags the others down with it. What is even more
telling, I think, is that some manufacturers using SAD's have
redundant protection using - yep - MOV's! Why not go with
MOV's right from the get-go. It's less expensive and safer.
Poly uses redundancy too, additional MOV's in case the
original MOV's go; and many products have status monitoring
to tell you if the MOV block requires replacement.
The MOV has its problems too. It can explode, which while
a rare occurrance, is why Poly uses metal containers. I am
quite leery of the plastic encapsulated suppressors using
MOV's. Oddly enough, UL would not approve Poly's products
because of the metal casing! Fortunately,Congress passed the
NRTL bill. NRTL is Nationally Recognized Testing Laboratory,
and there are several on that list. NRTL approval is equivalent
legally to UL. A NRTL passed the Poly products.
If I were looking at a suppressor to be palced at the service
entrance, I would go with a Poly MOV. For individual outlet
protectors, I would go with Poly again, but the products by
Panamax, Transtector, Northern Technologies, etc. are all
probably acceptable. Because lightning can induce a haeavy
surge in the wiring (after the service entrance protector), I
would follow Poly's grounding procedures for the outlet protectors.
Yes, Panamax, APC, Best, and probably others have insurance
coverage. Read the fine print please. While I am not a lawyer,
every other member of my family is, and the long and the short of
it is that YOU have to prove that you followed all the do's and don't's
of hooking the product up. I suppose a picture or a camcorder movie
of the installation could prove your compliance, but can you prove that
at the second prior to taking the hit the installation was still in compliance?
When your room or house is a charred mess, it is difficult to prove the
situation unless the investigator is quite the expert.
Of course, the best protection still remains the #1 Iron golf club atop your
tower or chimney. As Lee Trevino once said, "not even God can hit a
#1 Iron." And he should know, he's been struck by lightning at least twice!
73,
Bob AA0CY
----------
From: Ed - K0iL[SMTP:k0il@mitec.net]
Sent: Friday, July 30, 1999 8:43 PM
To: 'Towertalk@contesting.com'
Subject: RE: [TowerTalk] Lightning prot. (& bases on slopes)
Greetings TTers:
I'm curious if anyone has heard of SADs or Silicon Avalanche Diodes?
They're supposedly better than MOVs (on power lines). I rcvd info a while
back from a company called Transtector who sells these devices but haven't
had time to fully investigate them. Is anyone using these in any AC
protectors? Are they really better, and if so why isn't everyone designing
protectors using SADs?
On a more direct tower subject: What are your collective thoughts on
installing a tower base (for a freestanding tower -- an HDBX48) on sloped
ground level of about 10 degrees?
A. Do you just dig deeper (one foot deeper) so that on the uphill side
it's 4.5' deep plus 6" above grade, and on the lower side goes as deep as
the manufacturer's spec says to (3.5' + 18" above grade instead of just
6")?
-or-
B. Can you split the difference so that high side is 6 inches deeper than
spec (4' deep + 6" above) and low side is 6 inches short of it (3' deep +
18" above)?
Tnx much.
73,
de ed -K0iL
On Thursday, 29 July, 1999 8:40 PM, SavageBR@aol.com
[SMTP:SavageBR@aol.com] wrote:
> Be careful, the mainline protectors usually are not rated to protect to a
> level that protects electronics like computers. Additional surge
protectors
> are usually required.
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