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PE4BAS Amateur Radio Weblog

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Complexity of a HAM shack safety earth (ground)

Posted: 19 Dec 2021 01:59 PM PST https://pe4bas.blogspot.com/2021/12/complexity-of-ham-shack-safety-earth.html




It has been a while. Unfortunately personal things happened. And we all
got covid-19. So, we had some difficult times the last 2 weeks. Hope to
pick up writing again anyway.

Due to being not able to get to my job I had some free time after I had
some health issues due to the virus. I decided to do some work in the
shack. Something I should have done months ago. But....no time and didn't
feel like I had to do it. Might be not to urgent although the problem I
want to write about gave some serious safety issues.
For the last couple of months I had serious problems to get power into the shack. When switching on the mains the earth leakage circuit breaker would
trip most of the times. Unfortunately replacing the switches wasn't that
easy so the problem was getting worse in time. It was indeed that worse
that at some moment I couldn't even switch power off because the contacts
were simply welded together! Well, I finally had some time to take a closer look. As seen on the photo, the switch was not repairable. I didn't want to
use the same switches as well because it is evident that they are not good
for this task.
I did invest in some better switches. Of course they cost at least 5 times
more as these simple switches. But hope they are a lot better. Previously I switched both L and N. Now I only switch the live wire.
The photo shows when I just removed the old switches. I use one switch to
power on the computer and other appliances. The other switch is for the transformers feeding only the transceiver. The PSU in use is galvanically
not connected to the mains of the house. It is separated by a 1:1
transformer. I really don't know if this helps to minimize interference for
all kind of switching transformers on the mains net. But at least I like to believe so.

The new switches are installed now. I also renewed the cabling. I have to
say it looks very nice but different from what I use to have installed. I
did a search in my archive and found some post I made in 2013 about the electricity in my shack: https://pe4bas.blogspot.com/2013/08/radioshack-update-6-electricity.html





Another issue I had was with my safety earth system. Since I do power my transceiver through a "safety" transformer I don't use the house safety
earth system. However, the computer does ( I thought it didn't). I also
have a separate earth rod outside especially for the shack which is
connected with a thick copper cable to the coax entrance patchpanel near
the wall. It is not a RF ground but just for safety in case of static or
worse a direct lightning hit into the tower. What happens is when I want to plug in the USB cable from the computer to the IC-7300 I get shocked! I measured why and there is at least 100V between my computer and my IC-7300. Clearly this is a earth potential problem, as long as the USB cable is connected there is no problem because everything has the same potential. I didn't have a simple solution for it since whatever I thought I should do
it would give me a groundloop which I want to prevent. I didn't want to disconnect the house safety earth from the computer as well. The main
problem in a HAMshack is probabely the outer screen of the coax, since that
is also a conductor and connected to everything earthed from your
transceiver. I actually used it as my "safety" earth and did not connect
the starpoint of my counterpoise/RF earth to the earth rod because it would make a groundloop. But what if I disconnect the coaxcables from the
entrance patch panel? In that case the earth connection would be gone. A dangerous situation in case of a malfunction. Yes, the USB cable would
still ground my radio to the house "safety" earth. You see, but what
if....the question kept playing in my head. Even reading my own article
about the subject didn't give me the right "feel".
In the end I think for a good safety earth everything should have equal potential. You can only get that by bond all wires together and don't rely
on the outer screen of your coax cables and yes it will give you
groundloops. And yes, I know the separate groundrod should be connected to
the house safety earth groundrod to prevent these kind of problems. But unfortunately this is impossible since I have no access to the house
groundrod. I decided to minimize the groundloop effect by using a few #31 material ferrite clamps at least every meter and wind the earth wires
through it. At the moment I have permanent earth wires to the wall socket
of my computer and connected both house safety earth wire to my shack
ground as well as the starpoint of my counterpoise. The PSU is grounded to
the starpoint and again used ferrite to break groundloops.
Finally the 100V difference between computer and TRX is gone now. I didn't notice any difference in receive or transmit yet. But didn't try all bands
yet either. At least I feel a little safer now, though in a few years I
could have a different view on this complicated matter.
Sorry if you find this blogpost a bit chaotic. It looks like the virus has blurred my mind. The whole installation of the switches and adding a few
earth cables took me at least 2 days. Normally it would only took me a few hours. I had to think long before every step.

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