In a message dated 96-10-17 01:52:35 EDT, you write:
>
>Referring to W8JIT's suggestion to connect the coax shield to the power line
>neutral: as a working journeyman electrician, I was alarmed to see this
>suggestion. DO NOT DO THIS. IT IS UNSAFE. Here's why: If a load is on
>the line downstream, and the neutral conductor fails (opens) between your
>connection and the breaker panel, then your coax shield will be at 120
>volts, minus the drop across the load. But, if the neutral has opened, there
>will be no line current through the load and therefore its voltage drop will
>be zero; and your coax shield will be at 120 volts to ground!
Woops. Thanks for pointing that out.
Did I say neutral? I meant to say safety ground, not neutral. That is the
connection made to the outside of metal outlet boxes, and the retaining screw
of the wallplate, or the third round pin of the outlet. Actually all the
grounds, including the cable's, should be connected at the house service
entrance. That reduces all sorts of risks, including lightning.
If you use any capicitors on the outlet be sure to use flame proof power line
rated type caps, not little 1 kV disks. .01uF is plenty large. And put them
is a flameproof box or case.
I'll have to watch my wording closer, because I should have said the safety
ground or specified the connection point.
I don't follow the comment about cutting the wide blades of the plug off, but
the biggest worry is some igmo wiring the house backwards or a broken wire
from the outlet to the fuse box.
If a neutral opens from the line to the box, the whole ground system gets hot
anyway... including the safety grounds. I never could understand all that
work just to tie the stuff together at the fusebox and power line transformer
anyway, hi.
73 Tom
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Sponsored by Akorn Access, Inc & KM9P
|