I once measured 60VAC between the safety ground on stage and at the FOH shack, out in the field. This was at an outdoor amphitheater venue back in the woods. We got it sorted...
JR
JR
Driving a new ground spike
- Thread starter Tubetec
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nielsk
Well-known member
I suggest reading Audio Systems Design and Engineering by Philip Giddings for excellent and concise explanations of Technical Power Systems and proper shielding. In it you will find why "There are many examples where disconnecting pin 1 at the receiving end actually improves performance" because that is a proper implementation of telescoping shield ground.
Once again, a small system like a laptop with "most USB audio interfaces are ungrounded plastic boxes" (and likely powered from a laptop that uses a battery) is a very different situation than a full blown recording studio, and I maintain that the primary reason "Most commercial pro audio devices sold today are not earth grounded at all" is because of the pursuit of maximum profit, not quality.
Much of the reason for implementing various approaches of grounding and / or lifting in devices and their power supplies & cords in modern devices is to idiot proof them and reduce the back end support to customers who lack the knowledge to properly interface their equipment.
As to "how "noise currents " could flow "from the Neutral system into the Technical Ground system", this commonly occurs when the Neutral is bonded to the Ground inside a power panel which has many feet of cable (and it's inherit resistance) between a single ground rod and the panel. Any imperfection in the connections additionally decrease the ability of the ground system to sink current.
I have seen over 10 VAC measured on the Neutral system bleeding into the Ground system eliminated by proper implementation of a multiple ground rod system, and this DOES affect the noise floor of the audio system.
Once again, a small system like a laptop with "most USB audio interfaces are ungrounded plastic boxes" (and likely powered from a laptop that uses a battery) is a very different situation than a full blown recording studio, and I maintain that the primary reason "Most commercial pro audio devices sold today are not earth grounded at all" is because of the pursuit of maximum profit, not quality.
Much of the reason for implementing various approaches of grounding and / or lifting in devices and their power supplies & cords in modern devices is to idiot proof them and reduce the back end support to customers who lack the knowledge to properly interface their equipment.
As to "how "noise currents " could flow "from the Neutral system into the Technical Ground system", this commonly occurs when the Neutral is bonded to the Ground inside a power panel which has many feet of cable (and it's inherit resistance) between a single ground rod and the panel. Any imperfection in the connections additionally decrease the ability of the ground system to sink current.
I have seen over 10 VAC measured on the Neutral system bleeding into the Ground system eliminated by proper implementation of a multiple ground rod system, and this DOES affect the noise floor of the audio system.
Speedskater
Well-known member
We are co-mingling:
a] 'ground' = common reference point or common tie point
b] Planet Earth
c] Safety Ground/Protective Earth
d] Technical Ground this is a sub-set of [ c ]
a] 'ground' = common reference point or common tie point
b] Planet Earth
c] Safety Ground/Protective Earth
d] Technical Ground this is a sub-set of [ c ]
Wow , weve opened a right can of worms here . It'll take time for me to catch up .
I think you mentioned your neighbours lethal extension cord before John , I presume you rectified the issue before handing it back and gave him a thorough scolding for jepoardising peoples lives , Id have wanted to go over ,handcuff the guy to a radiator and put a crock clamp on his big toe , stand clear , testing ,bzzzt .
I probably did mention an ex army buddy of mine who ended up thumping a few officers at the end 'king of the castle' type war game , They wired him up to an old fashioned field telephone in the end , applied voltage to his neither regions , volts are directly proportional to the speed the handle is cranked .
'Resistance is futile , The Borg' ,comes to mind ,ahaha
I think you mentioned your neighbours lethal extension cord before John , I presume you rectified the issue before handing it back and gave him a thorough scolding for jepoardising peoples lives , Id have wanted to go over ,handcuff the guy to a radiator and put a crock clamp on his big toe , stand clear , testing ,bzzzt .
I probably did mention an ex army buddy of mine who ended up thumping a few officers at the end 'king of the castle' type war game , They wired him up to an old fashioned field telephone in the end , applied voltage to his neither regions , volts are directly proportional to the speed the handle is cranked .
'Resistance is futile , The Borg' ,comes to mind ,ahaha
What are the physics behind this "sunk to earth" idea? Since current flows in a loop, are you implying that there is some electrical source in the earth which takes a circuitous path through the wiring and needs to return to earth to complete the circuit? Or something different?
I may not have read this particular book, but you must have realized I already know the subject, having mentioned it.
Is there anything wrong with this? Does it result in sub-par performance?
If the equipment and connections are properly shielded electrostatically, these 10Vac should not matter at all.
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It could be argued that earthing is for safety and grounding is for noise. Earthing is not needed for making a clean system, once again the plane example demonstrates that.
The art is combining safe and clean.
I suspect there was quite a long distance between the point where you measured that and the distro board...?
And also that the equipment that produced that did not pass the conducted emissions test.
leadbreath
Well-known member
No it was at the PDU(Power Distribution Unit - Data Centre Equivalent to Distribution Board) when the electrician noticed sparks coming of the neutral bar when upgrading Circuit Breakers ,the lead engineer told him thats normal and placed a lead with 2 crocidile clips and linked the neutral to earth!!??? (I was witnessing the works and checked with dmm and we had about 107V on the neutra)
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leadbreath
Well-known member
Harmonics are a bitch....and it can also be caused by imbalanced 3 - phase systems but in this case it was due to harmonics....
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Not sure what this observation is meant to imply wrt the discussion topic here ? What was the wider picture wrt Neutral / Earth connection - which scheme / topology ?
Just to add that the shield does need to be 'Grounded' for E-field screening to be effective. Floating 'screens' or any floating conductor are likely to cause unpredictable and unwanted behaviour. H-field behaviour is a different issue as you go on to say.
re: "Grounded" - I think this term is responsible for a lot of the misconceptions around this topic. 'Ground' in this sense doesn't (have to) refer to a physical connection to the planet Earth. Hopefully we can all now agree that the 'planet' - a large mass rock / mineral / soil / water... - does not have any 'magical' electrical properties to sink/source current etc.
"Ground" as referenced for screening 'simply' needs to be held at a fixed voltage relative to the system ie have a low impedance connection to a fixed voltage.
Obviously, this is most commonly the 0V reference of the system eg in a vehicular system the battery negative.
In general detail E-fields are mostly reflected by metallic screening, some energy is absorbed in the screen and a finite amount passes through the screen.
All dependent on frequency / impedance / skin depth etc.
In practice almost any practicable foil works well. Anecdotally from the EMC front - the slightly thicker 'Turkey' foil that is sold over Christmas might give some real advantage over the 'normal' stuff but beyond that really no practical difference due to a law of massively diminishing returns.
Bo Deadly
Well-known member
Can you expand on this? My understanding is that if the circuit is completely enclosed the E-field will be isolated to the outer surface and the inner surface will have no E-field at all and that the screen will be equally effective regardless of whether or not it is grounded or not grounded because you cannot have currents without electric fields.
I rewired it correctly as soon as I discovered the fault.
I quickly determined that he was not smart enough to intentionally put me at risk. He blamed a relative for the faulty extension cord and if anything he may have been the target of mischief, or just ********* stumbling through life.
Reminds me of a funny internet meme... "when a mosquito lands on your nut sack, you realize violence is not the only solution".
JR
nielsk
Well-known member
It occurs to me much of what is being expressed here is typical of discussions on this forum, where some speak primarily from the perspective of experience in the field, designing, installing and maintaining large facilities with multiple interconnected rooms, and set up for live performance, live recording and broadcast, while some others speak primarily from a perspective of a classic education in E. E., and designing and developing products for manufactures. Possibly reduced to theoretical VS. empirical?
Theoretical Physics is a wonderful thing and what has led to much of what we get to work and play with, but there is no arguing with actual results in the field. It usually does not take long for someone working in the field to encounter horrible problems resulting from improper grounding and shielding.
Theoretical Physics is a wonderful thing and what has led to much of what we get to work and play with, but there is no arguing with actual results in the field. It usually does not take long for someone working in the field to encounter horrible problems resulting from improper grounding and shielding.
I'll 'subcontract' this to Harvard
extract: It is well known that no electric fields exist inside a hollow conductor, even if there are charges present outside. The conductor acts like an electrostatic shield. This is only true if the conductor is kept at a constant potential. Indeed, assuming electrostatic equilibrium and the concept of equipotential surface, one can argue by contradiction that there cannot be an electric field inside. Even though Gauss' law proves that it must be so, the nuances prevent many students from appreciating what's going on. Using a "segmented shield," one can demonstrate that electrostatic shielding doesn't work when the potential is not constant. When it is constant, the shielding effect arises from superposition of the field from the outside charge distribution and the opposing "back-field" of the hollow conductor. The "back-field" is directly observable in this demonstration.
Electrostatic Shielding
On a practical level it can be observed to be the case in an EMC Test Lab etc.
True in principle, but how practical is a circuit completely enclosed in a faraday cage with absolutely no opening? Once you have an opening you have to worry about currents flowing around that opening and generating a voltage across the gap. And unless you just wanted to shine a light out the hole you created, the opening is probably for a cable, so now you have to worry about the cable acting as an antenna carrying signals in or out of the enclosure, which leads to concerns about the common mode voltage of the enclosure relative to what is inside the enclosure, and what is outside the enclosure that the circuitry inside the enclosure is connected to via the cable(s) which now break the shielding. Sorry, my English teacher wife would give me grief about that horrible run-on sentence, but I think you get the idea, that different considerations come into play in the real world.
Yes, typically from so-called "pin 1 problems" that should be obvious from theoretical considerations, and which have been widely publicized since the 1995 Journal of the Audio Engineering Society special issue on grounding and shielding.
While there are quite a few people with academic background who do no understand the subtleties of real-world implementation, the problem with not having any theoretical understanding is that leaves one prone to misunderstanding the true cause of an observed phenomenon, fixing problems in other than the most efficient or robust way, and incorrectly thinking that fixes for a particular model mis-design are generally applicable.
But you still need to 'ground' it (or more correctly tie it to a low impedance reference voltage) even for a complete shield.
Bo Deadly
Well-known member
Ok, so it seems there are two things going on here.I'll 'subcontract' this to Harvard
extract: It is well known that no electric fields exist inside a hollow conductor, even if there are charges present outside. The conductor acts like an electrostatic shield. This is only true if the conductor is kept at a constant potential.
1) The video at 1:37 explains "Since the copper strips are all at the same potential, the net electric field inside the cylinder is always zero as we move the rod around". Meaning the even distribution of charge on the surface equates to a net field of zero within. If there was any kind of hole or slit or even a kink in the shield, it would not evenly distribute the charge and therefore changes in the external E field would be observable.
2) Even if the shield is NOT kept at a constant potential, the net distribution of charge around the shield is still zero but these changes are still visible to the inner conductor. This is effectively capacitive coupling. If the shield is grounded, it forces the potential to be fixed at 0V and the coupling is shunted. If you drive the shield with a copy of the signal, it would reduce the capacitance of the line.
I have been enlightened!
