On Mon, 15 Mar 2010 08:55:50 -0400, Pete Smith wrote:
>I have my shack wired through a series of plug strips,
Pete,
What you're describing is quite common, and at one point I thought it was a
good idea. It is NOT. There are two problems, both important. First, the
use of MOV devices on branch circuits is a recipe for lightning DAMAGE, not
protection. That's because in the event of a strike, they are shorting the
pulse to equipment ground at the point of every MOV, but thanks to the
resistance of the green wire, every outlet is at a different (and very
high) potential. Any equipment connected into outlets at different
locations with signal wiring between them is likely to be damaged by the
strike. The more inductance in the green wire, the more likely and the more
severe the damage. I have heard MANY anecdotal reports of computer and home
entertainment equipment destroyed by lightning damage. Plugged into MOV
outlet strips, no antennas at all, only Ethernet connections or audio
cables connecting them together.
As to the second problem -- Several years ago, I was asked to fix severe
hum and buzz at N6RO's 6-transmitter super station just east of San
Francisco. It had been wired years ago by person(s) unknown, and that
wiring job was excellent, with steel conduit from a local breaker panel in
the shack to quad boxes and 240V outlets for each station. Over the years,
a half dozen multi-outlet strips had been added, rather than use outlets at
the quad boxes. I measured something on the order of 30mV between each
computer chassis and the associated radio chassis. That's what was causing
the buzz. The very simple power wiring and chassis bonding detailed in
http://audiosystemsgroup.com/HamInterfacing.pdf is the result of that work.
In about two hours, that station was buzz free. The executive summary is
that I got rid of all of the strips, plugged everything directly into the
original good outlets, bonded the outlet boxes together with copper braid,
and bonded the gear in each station together with copper braid. The only
material used was about 20 feet of copper braid stripped from some old RG8.
The whole house shunt protector IS a good idea -- if the house wiring is
proper (that is, all the equipment and grounds bonded together), a strike
coming in on the power line raises the ground voltage for the entire house
by the same amount when it shunts it to ground. With that in place, the
differential voltage due to a strike is limited to what's on branch circuit
wiring between the panel and your equipment. The only safe way to protect
those branch circuits is with a SERIES MODE suppressor, such as those made
by SurgeX or Brick Wall. In essence, they store the strike energy in a very
robust inductor, then discharge it slowly as a DC current after the event.
They are not cheap, but neither is our ham gear. :)
Disclosure -- SurgeX is well respected in the pro audio world, and most
good consultants have been specifying their gear for 10-15 years. About
five years ago, they hired me to write a tutorial for them on power and
grounding, and to teach classes on that topic at trade shows, and I still
do that. I was specifying their products for nearly ten years before taking
that commission, and I have a half dozen of their protectors in my
home/office, all of which I paid for.
73,
Jim Brown K9YC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|