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

[Michael Tope]

Luk,

Are you using the PA0FRI screen regulator circuit? If so, won't you need 
more than 360 Vdc input?

73, Mike W4EF.................

On 11/30/2024 3:07 AM, flynth at gmail.com wrote:
> I decided to replace the auto transformer arrangement with a custom wound
> 230 - 2*130V transformer.
>
> Could someone please verify J chose the voltage correctly, please?
>
> I need 350V at 45mA max. The shunt regulator has constant current of
> 35mA-45mA which results in up to about 16W of power turned to heat. I
> choose 50VA transformer in the following way.
>
> 350V+10V for losses or sags /1.41=255V AC
>
> I can order these transformers with a step of 10V up to 230V so 2x130V
> seems a correct choice.
>
> 73,
> Luk - SP4IT
>
> On Sat, 30 Nov 2024, 11:49 ,<flynth at gmail.com> wrote:
>
>> Now that you say it that way I start suspecting the auto transformer.
>> Assuming nothing is miswired (and I have to rewire anyway to route the
>> wires nicely - currently it's only a "working" setup) it is the only place
>> that is not fully isolated.
>>
>> As expected in an auto transformer the neutral just passes through to the
>> rectifier then minus of the rectifier is connected to the ground/case.
>>
>> I had RCD trigger before I fitted the auto transformer, but only once, so
>> it may have been a temporary short.
>>
>> This is not ideal. I have to use it as auto transformer as all normal
>> transformers I have, have far too high voltages. (for example a 230 to
>> 415,after rectifying it results in 580V. That turns into a pot of heat if
>> it has to be shunt stabilised to 350V. It's very hard to find 230-300V
>> transformer.
>>
>> The "auto transformer" is a normal 240-2*36V toroid but connected like
>> this:
>>
>> Low side of 240V is neutral that passes through, high side is connected to
>> live 240V, then low side of the first 36V is connected to that, high side
>> is connected with low side of the other 36V. Finally the remaining high
>> side has approximately 300V AC and goes to the rectifier. I think it is the
>> most likely culprit.
>>
>> 73,
>> Luk - SP4IT
>>
>>
>> On Fri, 29 Nov 2024, 20:20 Michael Tope,<W4EF at dellroy.com> wrote:
>>
>>> Luk,
>>>
>>> At least for amplifiers I've seen here in North America, the isolation
>>> between the chassis metal and the power mains neutral typically come
>>> from the HV transformer (and any additional transformers that are used
>>> for producing things like filament voltage, control voltages, etc). Do
>>> you have any connections between the lines on the primary side of your
>>> transformers and the grounding conductor? In other words, I am trying to
>>> understand why you need an isolation transformer to prevent RCD/GFCI
>>> trip when the transformers in the amplifier should provide that function?
>>>
>>> 73, Mike W4EF
>>>
>>> On 11/28/2024 3:52 PM, Lukasz wrote:
>>>> Hi Jim,
>>>>
>>>> It is similar here in the EU as far as I know.
>>>>
>>>> A typical way devices, are constructed here is that the ground
>>> (including
>>>> the case if made of metal) is not used as a normal current path in the
>>>> device. One sees current flow on that ground only in a fault scenario.
>>>>
>>>> This means RCD/GFCI protections can work as when it see any discrepancy
>>> in
>>>> the live/neutral current balance it shuts the circuit down.
>>>>
>>>> These rules normally mean one always has a return current path within
>>> the
>>>> device that is separate from ground (neutral, DC minus etc), but this is
>>>> difficult when the amplifier is entirely made of metal and one would
>>> prefer
>>>> to have a current return plane (for example the floor if the case)
>>> rather
>>>> than route separate connections for DC minus and RF ground.
>>>>
>>>> This is not how OLD devices were made. I have a couple of old lathes and
>>>> mills that do use the steel frame as neutral/ground(one connector called
>>>> PEN) . This is how, it seems, all tube amps are built I saw pictures so
>>>> far.
>>>>
>>>> So my question is, if one wants to build a tube amp in a modern way.
>>>> Properly grounded, is building a case within a case and electrically
>>>> isolating the two the only way? Or has anyone managed to build a tube
>>>> amplifier in a single grounded steel case. That works normally within
>>> the
>>>> usual electrical systems (with gfci/rcd protected circuits). If so,
>>> please
>>>> describe how are all the current return paths done.
>>>>
>>>> 73,
>>>> Luk, SP4IT
>>>>
>>>> On Wed, 27 Nov 2024, 23:05 Jim Brown,<jim at audiosystemsgroup.com>
>>> wrote:
>>>>> 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
>>>>>>