Mark Smith wrote on Mon, 31 October 2005 12:12 |
While ground loops can cause hum, I can't think of a situation where you could have enough current capacity to cause a problem... Maybe with two completely seperate services and grounding systems, but you still usually have no more than a couple of ohms impedance between the two grounds and that is an outside number. Any thoughts?
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Yeah, in the church scenario, two grounds with enough current to kill may sound far fetched until you realize 20 to 50 milliamps is all it takes.
Then add water. Body resistance drops extremely low.
Add voltage to a wet human body, conductivity is sure to increase (resistance drops). Much like an arc through air as an analogy, air measures near infinity Ohms until broken down by conduction of an arc.
Not to mention the capacitance in the body too. It passes AC.
Even 1 volt, at 1 ohm, kills a person 20 times over.
My initial response was aimed at what could've possibly gone wrong on a professionally installed system.
NOTE! Even with GFCI's, if it WERE two grounds, it IS possible that a GFCI would NOT have helped, because the grounds don't get interrupted by the GFCI. Nor do grounds get interrupted by circuit breakers.
Far fetched? Not when a person is touching an electrical object in a pool of water.
This is one situation of the "flip side of the coin" where grounding can actually kill. Had the power system been floating, (such as an ungrounded balanced 120 Volt system) or, had the mic been ungrounded, there would have been zero potential as he charged the mic case.
But in the above paragraph, unbalanced/ungrounded 120 volt systems do not exist. So we MUST keep things grounded. Or someone else will eventually energize it high, or sink it to ground for you. We dedicate the grounding conductor, and keep it standardized.
The most likely situation is that the pool became energized hotter than the mic ground, and he got killed. The mic was most likely grounded through audio shields, even IF a power ground lift adapter was used somewhere. Case grounds, audio shields, and metal enclosures always seem to find earth one way or another. A GFCI WOULD have helped in this "likely" situation.