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Joined: Jul 2004
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I will reinforce the folks who say the coil is a bad idea.
It slows the leading edge of the spike and while that is happening it can go the other way.
In surge protection we do exactly the opposite. We put inductors (ferrite beads) in the signal lines and very short, straight grounding conductors. The theory is, by the time the shot could get down the signal lines, the ground has shunted it out. I know one engineer who swore tying a few overhand knots in the power cord would mitigate a transient. A lot of people told him he was nuts but if you looked later they had a few knots in their power cords. A ferrite bead is a lot better.
Greg Fretwell
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Joined: Jan 2005
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Mike, I was highlighting one of the quirks of the wording in our code.
Green, or green/yellow, is reserved for the 'equipment grounding condustor' alone. That's the 'earth' wire from the receptacle to the panel. This is also sometimes referred to as the 'bonding' conductor.
The wire from the panel to the ground rod to the panel has a completely different name: the 'grounding electrode conductor,' or GEC. No color is specified; indeed, it need not be insulated at all.
The same issue arises with the 'water bond,' or wire from the panel to where the water line enters the house.
So, we look to other parts of the code which reserve other colors for specific uses. The only reserved colors are green, green/yellow, gray, white, and in one special circumstance, orange.
In common practice, the wire is solid and bare, while the similar 'water bond' wire is stranded and has black insulation.
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Joined: Dec 2001
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6mm2 main earth? What service conductor size would that typically be used with? (here I think the main earth/PEN bond has to equal the cross-section of the phases, usually ends up being 16mm2 or up).
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Joined: Jan 2005
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I suppose that's another difference between our codes!
Here, while larger conductors are often specified, the largest wire we're ever REQUIRED to run to a ground rod is #6, which is (seat-of-pants guess here) perhaps 12mm2.
A lot has been written on the topic, but it all boils down to this question: Just what doest the ground rod do? Whatever else it does, it certainly does not help to clear faults.
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Joined: Jul 2002
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6mm2 main earth? What service conductor size would that typically be used with? Ragnar, That would be used with a 16mm˛ phase conductor, note that this only applies to single phase 230V installations. Anything poly-phase would have a minimum earthing lead size of 10mm˛. Here, while larger conductors are often specified, the largest wire we're ever REQUIRED to run to a ground rod is #6, which is (seat-of-pants guess here) perhaps 12mm2.
A lot has been written on the topic, but it all boils down to this question: Just what doest the ground rod do? Whatever else it does, it certainly does not help to clear faults. John, #6 is equivalent to 10mm˛. Believe me, I've seen some pretty weird things offered up as an Earth Electrode in my time, it seems to be the further you get out in the rural areas here, the more bizarre they become. One old guy once tried to convince me that wrapping the Earthing Lead around an old axle off of a tractor (with the wheels and tyres still on it) and burying it, "should comply with the most stringent of electricity regulations". 
Last edited by Trumpy; 09/26/10 04:07 PM. Reason: Typo's
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Joined: Dec 2001
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According to that table, #6 would be pretty close to 16mm2.
Why are there such considerable differences between stranded and solid conductors? Around here, we use the total cross section, e.g. stranded 1.5mm2 means a wire with a number of strands, the sum of strand cross sections equaling 1.5mm2. So 1.5mm2 ist 1.5mm2, regardless of whether it is stranded or solid. The effective current carrying capacity is the interesting thing, not the cross section of the wire itself (there IS a considerable difference in that regard, which is why I hate using stranded wire for fixed wiring where space is ntoriously tight).
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Joined: Jul 2004
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There does seem to be a problem with table 8. The sq/mm and sq/in is bigger with stranded wire but the resistance is higher. I bet they just use the area of the outer diameter, not the cross section of the strands. http://gfretwell.com/electrical/Table%208.jpg
Greg Fretwell
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Joined: Jul 2002
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Greg, I've always found with Imperial-Metric conversions there is always some sort of a concession. Wires over here are stated as {so many wires @ a given measured diameter), therefore we have something like 4.0mm˛ that has 7/0.85mm in the conductor twist. That list of Table 8 makes me wonder if we don't have accountants in there somewhere. I've never seen a 1.3mm˛ wire here, mind you, with inflation the way it is these days, you just never know. 
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Joined: Jul 2004
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Table 8 is just what you get if you have a calculator and a lot of time on your hands.
It is clear the area in in2 or MM2 in that table is just what you get when you compute the area of the circumscribed circle at the widest diameter, not the cumulative area of the strands.
The metric numbers are simply the calculated size, not any trade size you would find in a metric country.
It does make me wonder if there is some rounding going in in the actual wire since that is an international commodity. I know we can't really get 1/2" plywood anymore except for a few specialty suppliers. It is 12mm that they call 15/32 and most people think of as 1/2".
I guess I should get some wire and "mike" it.
Greg Fretwell
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