[Amps] Preventing current flow on PEN/EGC (protective earth conductor/equipment grounding conductor).

[Jim Brown]

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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