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Old 31st January 2012, 01:11 PM   #3631
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First of all thanks for the interesting post

So, If I understand correctly, the only method you consider safe is connecting PNGD to safety ground via ESP ground breaker or at least a diode bridge (as parallel diodes).

I suppose that also PGND to safety ground is safe but not advisable for ground loops and/or noise injection problems, right?

Quote:
Originally Posted by AndrewT View Post
All of this has been posted by many Members on this Forum.
Probably I've missed it, BTW most of Nelson Pass' PS uses thermistors as the only path for fault current.

I've read somewhere also about the single power resistor as an effective method.

Maybe my informations are not complete or right and I appreciate your suggestions.

I appreciate less this sentence...

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Originally Posted by AndrewT View Post
It is completely irresponsible to give dangerous advice simply because you have not informed yourself.
I've simply trusted mr. Pass:

The power supplies of each channel are isolated from each other
electrically, except for a thermistor on each which connects the circuit
ground to the chassis and earth ground. In this way ground loops are
prevented, as the channels will typically share ground only at the source,
but the thermistors stand by to conduct AC line voltage to ground until the
fuse blows, in case of transformer or other such failure.

(from F1 service manual)

And many others, BTW.
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Old 31st January 2012, 01:18 PM   #3632
UnixMan is offline UnixMan  Europe
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Quote:
Originally Posted by AndrewT View Post
One fault should never kill anybody.
just make sure that whatever you put between the signal ground and PE can safely withstand at least more current than the local fuse(s) will allow.

Of course the case and PT (core and screen if present) must be always directly connected to PE. As should be any other metal part which can be earthed without problems.

To avoid ground loops, signal input/output connectors must be kept isolated from the case.
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Old 31st January 2012, 01:31 PM   #3633
soongsc is offline soongsc  Taiwan
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Based on my experience, when too large capacitance is used where Y caps should be used, the leakage current will create small shock. This tells me that protective grounding does not work as expected. This had been verified in a qualified lab with earth ground according to requirements. However, since the regulation requires it, a commercial product should adhere to it. Class II appliances do not have connection to earth ground, thus have a different set of insulation requirements.

Dario, in my switching power, loading it with too much capacitance will trigger the protective circuit.
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Old 31st January 2012, 01:32 PM   #3634
GloBug is offline GloBug  Canada
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Quote:
Originally Posted by UnixMan View Post
the safety scheme works by triggering the differential breaker (AKA Residual-current device): any unbalance current (that is any current not flowing back through neutral but flows through earth instead) above the safety device set point (max 30mA here in Italy) will trigger the breaker and cut the mains. Hopefully BEFORE anyone will come in contact with the failing appliance.

Although from a normative point of view things may be different, from a technical (and safety) point of view there are no problem whatsoever as far as you don't break (or substantially limit) the AC&DC conduction from circuit ground to PE in presence of dangerous voltages between the two.

Thus from a technical (and safety) point of view there are absolutely no problem if you insert a small valued resistor/thermistor, anti-series zener diodes, inductor, etc between signal ground and PE to open ground loops or limit their nasty effects.

Perhaps you may not get CE certification that way, but that's another story.
If your referring to what most would call a "GFCI", they are for "extra" protection in certain situations, I would certainly not rely on them, simply because they are not reliable.

Add to this a GFCI won't protect you from stored voltage in your device amplifier should it have such a fault.
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Old 31st January 2012, 01:37 PM   #3635
AndrewT is offline AndrewT  Scotland
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Originally Posted by UnixMan View Post
just make sure that whatever you put between the signal ground and PE can safely withstand at least more current than the local fuse(s) will allow.
I had used a low value resistor between Signal Return and Main Audio Ground.
That is until a Member posted a schematic in which I noticed he had a diode across that resistor.
That got me thinking about the exposed RCA barrel at the other end of an interconnect.

I now use inverse parallel diodes (1n400x) across all my low value resistors that may have to pass some fault current, irrespective of which end of the interconnect cable has the fault.
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Last edited by AndrewT; 31st January 2012 at 01:39 PM.
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Old 31st January 2012, 01:53 PM   #3636
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Quote:
Originally Posted by soongsc View Post
Based on my experience, when too large capacitance is used where Y caps should be used, the leakage current will create small shock. This tells me that protective grounding does not work as expected.
I don't understand... what are you referring to?

In the My_Ref there's no single place where a Y cap should be used apart the connection between IEC/fuse/transformer primaries...

Quote:
Originally Posted by soongsc View Post
Dario, in my switching power, loading it with too much capacitance will trigger the protective circuit.
Ok, so you were referring to the switching PS protection... now it's clear, thanks
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Old 31st January 2012, 02:01 PM   #3637
soongsc is offline soongsc  Taiwan
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We ran through some speakers and amps in listening tests. Very interestingly, the little modded amp presented more detail than another class A amp. Sound stage was pretty much the same, low frequency seemed more correctly damped to me while some preferred a looser beefier low end with small speakers. Sorry for not revealing the exact models because I did not really take care to note what they were. I am happy, but also see some more room for improvement.
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Old 31st January 2012, 02:05 PM   #3638
soongsc is offline soongsc  Taiwan
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Quote:
Originally Posted by ClaveFremen View Post
I don't understand... what are you referring to?

In the My_Ref there's no single place where a Y cap should be used apart the connection between IEC/fuse/transformer primaries...



...
I am talking about power ground protection in general. X and Y caps have very specific requirements when used for mains power filtering. What I am saying is that it's been confirmed you will have a shock when large currents pass through the ground line of the mains regardless whether you meet the requirements or not.
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Old 31st January 2012, 02:27 PM   #3639
AndrewT is offline AndrewT  Scotland
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....................I appreciate less this sentence.....................
I too would not appreciate that being said to me. But, if I was that irresponsible, then maybe that type of message is what I would need to wake me up.

I stand by what I said. Looks like you have been wakened up.
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Old 31st January 2012, 02:48 PM   #3640
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