[TowerTalk] Lightning Arrestor Question
jimlux at earthlink.net
Sat Jan 9 07:22:05 PST 2010
> I have a box at the base of my tower housing my DX Eng. antenna switch
> box that also provides a central entry point for all the antenna cables
> (prior to going underground to the house). Will placing an arrestor
> only on the output coax from the antenna switch to the house be
> sufficient or do I need to place an arrestor on each antenna line
> entering the box and switch (the shields are all grounded to the ground
> system in this box)? Additionally, do I need to place an arrestor at
> the house's central grounding point (where it enters the shack)?
> Overkill? The grounding system is all tied together (tower, switch box,
> house entry point, and home's electrical system).
> Thanks for any help/ideas you can give me.
First off, are you interested in "code compliance", in which case there
are specific requirements which you have to meet. Most important would
be the requirement for a listed "antenna discharge unit" and appropriate
bonding to the home's grounding system (which you might already have)
But that aside, a lot depends on what you want to consider potentially
sacrificial elements. if the switch is "outside" the protection, then
it's going to take the hit. On the other hand, a box o'relays is a
pretty tough item (compared to something like your receiver front end).
Depending on what the "rest" configuration of the contacts are, a
moderate transient may not cause a big problem. (i.e. unused ports
grounded, one live port is connected to a transient suppressor, so no
port can go very high in voltage) One of the more vulnerable aspects is
the coil and its related circuitry. A transient could breakdown the
coil insulation, for instance, if the coil actuation wires wind up being
at a different potential than the relay frame (which is presumably grounded)
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