Hi Lukasz,
In North America, the protective earth MUST be carried in the same cable
with the current-carrying conductors, and MUST be bonded to the chassis
at the point where that cable enters. I'd be surprised if it's different
in EU -- it must be done that way to be protective!
There's another requirement in NA -- all grounds (earths) MUST be bonded
together. Again, protective against both lightning and electrical shock.
So when power goes through ANY transformer that's not part of equipment,
protective earth MUST be carried from one side of the transformer to the
other.
I don't remember about EU, but I do remember that in the UK, no earth
connection to the power system is permitted -- that happens only within
the power distribution system.
When thinking about this and antennas, remember that the earth is a big
resistor, and parts of antennas like radial systems are NOT intended to
couple to the earth, but rather to shield the EM field from the earth,
and to provide a low resistance path for the antenna's return current.
The only antennas that benefit from an earth connection are SOME
receiving antennas, like Beverages and loops.
73, Jim K9YC
On 11/26/2024 8:10 AM, Lukasz wrote:
Hi,
Is there some way to build a tube amp in a metal case, using the case as RF
ground, and not have current flow out of the amp through the grounding
conductor? (other than isolating that ground from the case entirely, which
presents it's own problems - for example capacitive coupling to the case).
I'm currently experimenting with an amp and I have to power it via an
isolation transformer (the high voltage is 3 phase on its own circuit with
no GFCI temporarily) or my RCD will trigger.
The high voltage power supply is an old military device that used its
chassis as ultimate DC ground (hv ground connects to it through a
overcurrent protection coil).
Then I also used the chassis as ground for DC HV, screen and grid supplies.
This I could swap, but it's the RF ground (especially the Pi tank) I'm
concerned about.
Is essentially isolating amp RF ground from the grounding conductor
(PEN/EGC or whatever it's called where you are) the only way?
73,
Łukasz, SP4IT
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