On Sat, 24 Jul 2010 22:15:43 -0500, Fred wrote:
>I have a grounding question for all you rf experts.
I suggest that you study the Power and Grounding tutorial that's on my
website. http://audiosystemsgroup.com/publish.htm It's in the section
on audio and video.
Also study the piece on Ham Interfacing, and in the RFI Tutorial, look
at the chapter on Solving Problems in the Shack.
There's one big problem with your installation. Building safety codes
require that the wire that connects the third round pin in the outlet
to the breaker panel be run WITH THE OTHER TWO CONDUCTORS. There are
three VERY good reasons for that. First, inductance -- if if follows a
separate path, the inductance, which is proportional to loop area,
increases the time that it takes a breaker to blow in the case of a
fault. Second, if something causes the ground to break, it should also
interrupt the hot and neutral. Third, when you bypass the hot (phase)
conductor to ground with a capacitor, the resulting inductive loop area
is very small if the ground is run with the phase and neutral, but very
large if they are run separately. That loop acts as both a magnetic
loop and an antenna to radiate power line noise, and it also picks up
your transmitted RF and puts it on the power line. Most equipment has
capacitance between the phase conductor and ground, usually in the form
of a line filter and in the capacitance to ground of the power
Because it can be so difficult to replace existing wiring like yours,
older buildings are "grandfathered" -- that is, they are exempted from
the legal requirement of grounded outlets.
But you want to be safer and have your station work better. In your
case, if you can run a ground wire up from the panel to your shack, you
should also replace the existing power wiring in your shack with new
power wiring that follows that path. You don't need to disconnect the
existing outlets, but simply abandon them (or use them for lighting),
and use the new wiring for your ham and computer gear. If it were me, I
would use #12 copper, and pull in two circuits. This allows you put
them on 20A breakers. If you need 240V in your shack, put those two
circuits on opposite legs, and wire the two hots to a 240V outlet. You
should put all of this in proper steel boxes that you can buy at any
good hardware store.
For your installation, I think you're moving in the best direction
possible -- that is, new ground rods, bonded together, bonded to your
shack ground. BUT -- they MUST be bonded to the power system ground at
the breaker panel.
73, Jim Brown K9YC
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