On Fri, 29 Nov 2024, 14:58 dj7ww@t-online.de, <dj7ww@t-online.de> wrote:
Hi Lukasz,
I use a tube amplifier which I have built in 1975 in a no RCD environment.
It uses a 3-phase HV power supply as well as single phase small power
supplies.
The amplifier is of course grounded with its chassis to safety ground (PEN).
The amp chassis is also RF ground.
B- is routed separate from the power supply to the amp but clamped to
chassis ground via a 10 ohm resistor and a diode, that is a requirement for
metering grid and anode current. Without metering it could be connected
directly to the chassis.
Power supply chassis and amp chassis are interconnected.
HV transformer is YY wired, rectifier is B6 full wave, so no neutral
connected.
Amp works with RCD now after I moved qth.
You might have a problem with your power supply when the RCD trips.
Very interesting. Do you have any additional DC voltages in there, relays,
grids etc. Do you also connect all these DC return paths to the case?
Perhaps something is miswired in my amp. Because this is exactly how I
planned my wiring (plus few DC minus wired to the case) but I'm activating
an RCD the moment I switch it on.
How is your grid wired, with what system?
It is called I believe TN-S and this picture sums it up nicely:
https://ibb.co/B3CgSnc
Bonding is only in the main panel.
In the shack I don't currently have 3 phase socket (but the wiring is
available so I'm going to add it) so 3 phase is coming in via a power
extension cord from the garage where there is no RCD on the circuit it is
plugged in.
The HV psu is powered via these 3 phases (no neutral connected, main
transformer is star connected because it was originally made for lower
voltage military 3 phase "field supply"), it's chassis is grounded to the
grounding pin in a power receptacle in the shack.
It uses a balanced 3 phase diode rectifier. I don't know, but I doubt DC
minus is connected to the metal case in the HV supply. I know the current
return goes through a relay coil to cut off power if too much current
flows.
The amplifier case is grounded via same power receptacle pin. But it has to
be powered via an isolation transformer to avoid RCD activating
(immediately).
Within the amp the HV DC minus it connected to the case through a current
measurement resistor and two diodes (that conduct both ways) to protect the
meter. The resistor is very small (made with about a meter of thin copper
wire) as the meter is a uA meter.
In the amp there is a 12v single phase toroid transformer that powers the
heater only. One leg is case connected.
There is +12V,0,-12V stabilised psu for the op amp required for the screen
voltage regulator. 0V is case connected (tiny 20VA 1ph transformer).
>From that transformer there is a voltage tripler/rectifier to get -55V for
the bias (again zero case connected).
Finally there is a 100va 1ph toroid 2*36V set up as an auto transformer to
bump 230-240V incoming into ~300V which is rectified (again minus to case)
resulting in ~430V (after a resistor) which is Shunt regulated (with quite
z bit of extra heat) to +350V screen supply. The same has ocercurrent
protection set to 35mA (4 diodes feeding an optocoupler).
So not much difference from yours in theory. BTW, before I fitted the auto
transformer I used a normal 1ph 230-420V transformer, but it produced too
high voltage. It still would throw out the RCD with the old one.
RF ground is connected to the case, as well as coax shields input and
output (at place of entry).
On Fri, 29 Nov 2024, 05:30 Jim Brown, <jim@audiosystemsgroup.com> wrote:
The primary cause of RFI to/from equipment is a cable shield or bonding
conductor that passes through an opening in the enclosure, wanders
around inside either on discrete wires or a PC board before it finally
hits the shielding enclosure. That's "The Pin One Problem" that you may
have heard about, where Pin One comes from the fact that Pin One of pro
mic connectors carries the cable shield.
I still remember the feeling when I finally learned about pin 1 problem and
I applied that knowledge to a previously built circuit with bad 50Hz issue.
At that time I was interested in electronics for a couple of years as a
hobby and I pretty much gave up on analog/audio stuff. That single thing
changed that.
What does "grounding" mean to you? What do you expect it to accomplish?
One thing is obviously safety, no one wants voltage to show up on the case,
but another reason is to provide a very low impedance return path for DC
minus. To lower the possibility it will pick up any RF.
If you mean a connection to earth, it is of value ONLY as part of
lightning protection, and for lightning protection, extensive bonding is
also required.
Do you mean what we call "bonding," which is connecting all earth
connections and protective earths together?
Bonding here is also done only in one place, where the electric supply
comes into the house.
In general I think these two things cover it. One, to make it as hard as
possible to pick up RF, and two, make the case potential as closed to the
earth/local environment as possible. Perhaps the third too, so the RCD/GFCI
can continue to work.and disconnect the power if current starts flowing on
thf ground connection.
Here in NA, our "house wiring" is 120-0-120, where 0 is the neutral, and
big power supplies run between the two sides of 120V. Neutral is bonded
to protective earth at the point where power enters our home.
This is very similar to us, the main differences are we have 3 phases
spaced 120 degrees instead of yours two spaced 180. And we have higher
voltage. But we too have devices that can next between two phases (my
induction hob) or even all 3 (tank less water heater).
Another difference between NA and here is that it is common here for entire
streets to be hooked up to just one big transformer. The utility service
usually comes as 5 wires (3 phases, neutral and the protective earth in a
form of a copper cable and a galvanised steel conductor that is in a trench
often hundreds of meters long). The PE on the supply side is there only to
provide touch safety for the steel supply cabinet, but many people connect
it to their grounding system illegally "for better ground" instead of
spending more money on ground rods.
Here,
GFCIs are required only in locations like kitchens and bathrooms, and
would not be required on circuits feeding a ham shack, bedroom, or other
living space.
I'm not entirely sure what the current code requires, but I know even since
many decades ago when I worked as an electrician's helper laying wires in
new built homes we would put in RCD/GFCIs everywhere and as many as
possible (it was not a requirement, but was considered good practice). But
the actual current threshold I believe is much higher than in NA. I once
heard in NA they have ones that activate somewhere near 5mA. We would
install 130mA ones for outside circuits and any large load that was for
example a water boiler. And we would use 30mA as standard everywhere else.
Bathrooms/Kitchens were not treated any differently, but at the same time
we never installed power outlets near sinks etc. Perhaps if we did we would
have to use more sensitive RCDs. This was just a few summer jobs for me as
a teenager helping his dad.
When an electrician installed the system in my house some 8 years ago he
did it the same way I'd do back then.
My shack is wired the same way as the house.
73,
Luk, SP4IT
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