[Top] [All Lists]

Re: [RFI] CHECK your grounds.

To: rfi@contesting.com
Subject: Re: [RFI] CHECK your grounds.
From: "K8RI (Roger)" <K8RI@rogerhalstead.com>
Date: Wed, 26 Jan 2011 18:53:54 -0500
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On 1/26/2011 5:49 PM, Jim Brown wrote:
> On 1/26/2011 12:29 PM, KD7JYK DM09 wrote:
>> I have taken photos of our electrical "grounds".
> You need to study the fundamental principles of AC power distribution. A
> GROUND conductor does NOT carry load current -- it's sole function is
> SAFETY.  The current carrying conductors are the Phase and Neutral
> conductors. A 240V single phase system has two Phase conductors and a
> Neutral conductor, fed from a center tapped  transformer. The two Phase
> conductors are connected to the two ends of the transformer, and the
> neutral is connected to the center tap. There is NO ground conductor
> between the power company and your home. Rather, the Neutral conductor
> is grounded FOR LIGHTNING SAFETY both at the transformer and at the
> point where it enters the building.  A separate Equipment Ground
> conductor (the Green wire) is carried with the phase and neutral
> conductors to every outlet, and to every piece of equipment wired
> directly into the power system. The purpose of that Green wire is
> SAFETY. It's function is to cause a fuse (or breaker) to blow if
> something goes wrong.
I'd add that the green wire is needed for ground fault breakers and 
outlets to work.
Also it causes the fuse or breaker (GFI) to go if there is a short (or 
leakage current to ground), but over current (as in a shorted 
transformer or tube) is likely to trip the breaker without ever making 
use of ground.

As you say the green wire is for safety and should never take part in 
carrying power for the actual operation of the equipment.

I once had a vertical in my West yard  about 50 feet from the West end 
of the house. (when I lived South of Breckenridge MI). The "shack" was 
in the basement on the South East end of the Basement. The equipment was 
grounded  directly behind the rig  about 40 to 50 feet East of the 
service ground.  The rig at the time was a Yaesu FT101B and IIRC only 
used a 2 wire power cord.  There was an overly generous solder 
connection on the power socket (from the factory) at the back of the 
rig. Moving the power cable would cause the pins to more around enough 
for that solder to contact the chassis of the FT101B with no apparent 
effects in the basement, or to the operator.  There was also an 8' 
ground rod under the 33' 40 meter vertical with the coax braid and 
radials tied to it.   That meant when the 120VAC went to chassis ground 
it was divided between the 8' ground rod just outside the basement wall 
and the one under the vertical with the service ground being *about* 
half way between them. No, most of us didn't even know what a single 
point ground was back then.

It was well into spring, the snow had melted and the yards were wet, but 
no standing water.  A number of the radials for the vertical had come 
loose and coiled up at the base of the antenna.  I took each radial, 
pulled it straight and stuck about 6" of it into the ground.  The ends 
of the radials had a 90 degree bend and they'd lay nice and straight.  
It was that last radial... I pulled it straight, but my back was getting 
tired so I knelt down to stick the wire into the ground. As soon as my 
knees hit that wet ground it had me.  In my hands and out my knees.  I 
couldn't let go. Fortunately being balanced on the balls of my feet, I 
fell over backwards. As soon as my knees broke contact I threw that wire.

The point being that even though the rig was grounded through two 8' 
ground rods about 50 feet either side of the service ground, there 
wasn't enough current to trip the 20A breaker. There was however enough 
voltage present that it could paralyze a person and that HURTS! Boy does 
that hurt and you can't make a sound.  Had I not fallen or fallen 
forward instead of backwards it's likely I'd  not be here today.  Had 
there been a single point ground, or the station ground tied into the 
house ground it would have popped the breaker as soon as the line to 
chassis occurred.

> The EARTH is a lousy conductor, and should NEVER carry current in a
> power system.  A connection to earth is almost never part of a solution
> to an RF or noise problem.
I'm a believer!


Roger (K8RI)
> There is a tutorial discussion of power systems on my website.
> http://audiosystemsgroup.com/publish.htm
> 73, Jim Brown K9YC
> _______________________________________________
> RFI mailing list
> RFI@contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi

RFI mailing list

<Prev in Thread] Current Thread [Next in Thread>