Many days I'm not in the club either. TOO many acronyms. And sometimes the same acronym means different things in different contexts. Its good practice to spell them out when first used so we are all on the same page.
I like showing real world conditions vs ideal, text book and often simplified data with assumptions.
So, I showed current flow, measured, flowing between two separate ground points (75 feet/ 25 meters apart) when connected together. Or thru a person.... All legally done.
Another unsafe condition may occure when you use multiple MOV protected power strips/conditioners. Leakage current of the MOV is designed to be under 5 mA. However, no one knows how many you have in parallel within your room/system/house. All in parallel and increasing current thru N-G. Easily exceeding 5mA safe limit total in many homes.
THx-RNMarsh
So, I showed current flow, measured, flowing between two separate ground points (75 feet/ 25 meters apart) when connected together. Or thru a person.... All legally done.
Another unsafe condition may occure when you use multiple MOV protected power strips/conditioners. Leakage current of the MOV is designed to be under 5 mA. However, no one knows how many you have in parallel within your room/system/house. All in parallel and increasing current thru N-G. Easily exceeding 5mA safe limit total in many homes.
THx-RNMarsh
Measuring current flow between two low impedance sources seems critically sensitive to the measuring device's impedance. A conventional instrument's very low impedance would be very much worst case. Wouldn't voltage be more appropriate?
All good fortune,
Chris
All good fortune,
Chris
I’d say there is a problem with that.
Anyway, in most audio set ups, you should come off a common mains outlet to minimize loop area.
The worst main noise problem I ever experienced was in a house in Taiwan. Two sockets about 1.5 meters apart. If I used both, system hummed like hell. Use only 1 and it was ok.
Taps tingled, breakers tripped - place was a death trap IMV. We eventually moved out, but for other reasons. (Oh, and huge amounts of mains noise).
Connecting two devices in a hifi system at home, it is a good thing to measure, before to connect the audio link between them, the respective AC phases that produce the less voltage between their grounds. (AC leaks)
R.N.Marsh is right. Once connected, as the impedance of the line cable is very low, the only thing you can measure is the current flowing across the ground wire of the line cable.
Very low, but not null. It will remain a parasitic voltage that is added to the signal reference. Low, but not null.
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Yes. This voltage difference makes hum into the cable, coming as a voltage difference in electric ground. In the case of balanced cables the hum rejection will depend of source and receiving impedances, that is why pros consider there should be at least a x10 factor between theses impedances.
Disassembled the first driver, pulled the basket off the magnet assembly, split the front plate in half, turned a brass spacer for re-gluing plate to magnets.
Interrupted by another unexpected and sudden death.
Sigh...
Twill eventually continue.
Jn
In the USA, circuits are either 12 or 14 AWG, the ground conductor is generally same as the current carrying conductors, the resistance is very low.
NEC absolutely requires that the grounding/bonding conductor cannot carry the current of the end load. Ever. Only when a hot to chassis fault occurs will the grounding conductor carry the fault current.
As several here have detailed, line conditioners can push current into the ground, but even 5 mA in a ten foot run of 1.2 mOhm/foot ground is 60 micro volts. So in a typical residence, you will not measure IR drop voltages.
That said, if you have two outlets daisied in a single room on opposing walls, and put a dvm between grounds, you can measure a volt or two even if no current is flowing in the cable. This is consistent with making a 15 foot diameter loop of wire and seeing what it picks up.
That is induced voltage from the constant 60 cycle field we choose to live in.
Jn
Is that what everyone has/does?
It is not unusual in larger bi-tri-ampd systems including a video/surround system which uses the audio... to use more than one power outlet in a room. More than one ac power strip with MOV inside.
Some ac outlets on a wall are wired to another ac recept in other room -on opposite side of wall. Connected to another MOV strip in adjacent room. .
Lots of room for increased G-N currents adding. I can think of many others.
One CB (Circuit Breaker) can be wired to many outlets in a home including the one used for audio.
The total leakage current is often much higher than assumed.
THx-RNMarsh
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Having 5mA run through the grounding conductor is not unsafe, nor is having multiple conditioners running 15 or 20 mA through the the house ground.
Your definition of "safe" limit is the let go threshold limit for current flowing hand to hand at 60 hz for a human male weighing 150 lbs (yah, I wish I were there) that Charles Dalziel measured by human experimentation years ago. It is not a wiring safety.
More than one conditioner on a single GFCI (ground fault circuit interrupter) protected branch can lead to nuisance trips, so some would then remove the protection for convenience which is much more dangerous.
Jn
Note: the DC let go threshold was historically 40 mA, but should be 25 mA (the Europe standard), as let go is correlated to weight, 5% of women at 115 lbs cannot let go at 40 mA.
Ps. If one has a large AV install with multiple conditioners, use multiple GFCI's at the setup, each protecting a conditioner.
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That isn't normal for UK where you should have a ring-main in each room, which brings its own issues with Maximising loop area.
But of course there are still various abominations that people have snuck in before laws changed.
Sorry, you made more than typos :
It was about the twenty-first century, not the twentieth century.
The adjective was spiritual, not religious.
And... Malraux clearly denied that he was the author of this assertion !
What he said is more uncertain:
"I do not exclude the possibility of a spiritual event on a planetary scale."
( source : Dieu etait <<mort>>, il est <<de retour>>... On est en pleine confusion | Slate.fr )
True, and, it generally wouldnt be so convenient in a brick or concrete wall/building.
But in stick frame construction (USA) the ac power wire is same for either side of the room/walls. Unless, you run a dedicated ac line only for your audio only system, you have high potential for many other powered items on same line... some not in same room. Therefore, total leakage to ground is rather higher than you would like. Espec if several MOV are hanging on it in multiple places along the line.
The ground current flowing thru CATV coax shield was a single path, only. 15mA. NOT a worse case with all equipment connected/powered.
JN --> Maximum Let-Go Level. The maximum Let Go Threshold level for a female is approximately - 9 mA and for a male it is about - 15 mA.
THx-RNMarsh
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I have Dalsiel's original research paper with the associated data and graphs, it is there I found the numbers. It's been a few years since I did the research, so I'll re-examine the data.
I do not consider a 2% level to be acceptable..meaning 98% of people can let go at the current, as that means 2% can't.
I earlier said 5% of women cannot let go of 40 mA, that was incorrect and should be 2%.
jn
just missed the timeout.
Dalziel's data is .5% cannot let go.
I go by IEC TR 60479-5. Figure 1 shows the requirements. Note that the let go lines for AC and DC hit 5 mA and 25 mA respectively, with the AC line at 7 seconds, the DC line at 2 seconds. Below those lines is considered "infinite duration", while above is "risk of muscular reactions".
NEC uses the term "average healthy young" in 70E. Old, decrepid guys like us, petite women, fall outside the phrase "average healthy young". Darwinism is not acceptable.
I choose the safer limits because I'm an old out of shape decrepid guy.. 😀
jn
Dalziel's data is .5% cannot let go.
I go by IEC TR 60479-5. Figure 1 shows the requirements. Note that the let go lines for AC and DC hit 5 mA and 25 mA respectively, with the AC line at 7 seconds, the DC line at 2 seconds. Below those lines is considered "infinite duration", while above is "risk of muscular reactions".
NEC uses the term "average healthy young" in 70E. Old, decrepid guys like us, petite women, fall outside the phrase "average healthy young". Darwinism is not acceptable.
I choose the safer limits because I'm an old out of shape decrepid guy.. 😀
jn
I was not talking about the earth (or ground) of the AC plug, but the grounds (or the shields) of signal cables . The parasitic voltage I was talking about is produced by leaks in the two power transformers (both magnetic and capacitive) between primary and secondary, yhat appears even when both are powered from the same AC plug.
Over here, we have an RCD (residual current device) which I presume provides the same function.
A tripping level of 30mA appears to be the standard for our 230V mains supply.
I read that 10mA is standard for a 120V supply - is this correct?
I see that 10mA RCDs are available for use on our 230V supply, presumably for the ultimate in protection.
Ours are... absolutely trip at 6 mA, never trip at 4. But that is COTS consumer residential equipment. (Commercial Off The Shelf.)
Industrial can have higher trip points, sometimes programmable.
jn
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