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Old 7th February 2007, 03:27 PM   #1
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Default Grounding and Interfacing in Audio

I have seen many questions concerning Grounding in Audio Projects rise in the Forum. There is an excellent article by Gary Galo available online at www.Audioxpress.com covering this topic. No subscription is required. The whole concept of what constitutes Ground is discussed as well as proper procedures neede to arrive at a good grounding situation. Give it a try!!!Perhaps you can add something of value.
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Old 7th February 2007, 07:17 PM   #2
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Good article. Been reading Whitlock's stuff for years. Nice to see that Gary Gallo's giving it some broader exposure.

Here's a direct link to the article for those who may have trouble finding it on the AudioXpress website:

Grounding and System Interfacing

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Old 7th February 2007, 08:28 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
Just started to read Galo's article and noted that the Whitlock sketch (page1) is wrong.

It states that the chassis is at 0V potential during the fault condition.

When the conductor sizes in the supply cable are correctly proportioned and the Breaker panel is correctly designed/assembled the voltage on the chassis can rise to near 50Vac.
If environmental conditions are such as to make this voltage/fault current flow through a touching human then sufficient energy is available to at least injure and possibly kill before the fuse blows.

It's a pity Galo did not spot that error nor draw attention to the lack of absolute safety that correct fusing and correct eathing provides.
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Old 7th February 2007, 10:46 PM   #4
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Quote:
Originally posted by AndrewT
When the conductor sizes in the supply cable are correctly proportioned and the Breaker panel is correctly designed/assembled the voltage on the chassis can rise to near 50Vac.
But that 50 volts on the chassis that you state would only be relative to the neutral connection back at the service panel, no?

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Old 7th February 2007, 11:20 PM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
that 50Vac or so, in worst case conditions, is relative to the ground (earth even) that we are standing on.

Fortunately, to develop that high a voltage between chassis and the mains source, the current must be very high and this high current must of necessity break the fuse fairly rapidly.
The rapidity of breaking exposes us to the elevated chassis voltage for a very short time (from fault occurance to dead appliance) and it takes a number of low probabilities to occur at the same time for the shock hazard to actually cause harm. I guess that some committee decided on balancing these probabilities and determined an acceptable risk that was somehow turned into a cost/life.
The result, at least with UK regulations, is that properly earthed equipment used and fused corrrectly rarely electrocute.

But that does not excuse the erroreous statement nor the overcite that allowed it to be re-published.
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Old 8th February 2007, 04:27 AM   #6
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Quote:
Originally posted by AndrewT
that 50Vac or so, in worst case conditions, is relative to the ground (earth even) that we are standing on.
Ok.

Quote:
Fortunately, to develop that high a voltage between chassis and the mains source, the current must be very high and this high current must of necessity break the fuse fairly rapidly.
Yes. Because there is a low impedance path back to neutral by way of the safety ground.

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The rapidity of breaking exposes us to the elevated chassis voltage for a very short time (from fault occurance to dead appliance) and it takes a number of low probabilities to occur at the same time for the shock hazard to actually cause harm.
Right.

But the path from the equipment chassis, through the earth, and back to neutral is in parallel with the ground fault path you mention above, so whatever voltage potential may exist between the chassis and earth would last no longer than it takes for the fuse to blow or the breaker to trip.

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Old 8th February 2007, 02:04 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi Steve,
yes.

And I even had the brass neck to ask Bill Whitlock for a copy of his presentataion.
I have read a few of his papers and usually his arguments are bullet proof, pity that one escaped.
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