Re: The dowel of death - SAFETY

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mike Harrison by way of Terry Fritz <twftesla-at-qwest-dot-net>" <mike-at-whitewing.co.uk>

Before we digressed into the conducting properties of various
materials, the question was why shocks were felt despite the end
electrode being grounded, and whether the inductance of the ground
wire was significant.
 I think the answer is yes and no. Although the inductance of the
ground wire is probably insignificant for the TC fundamental
frequency, a spark discharge has an extremely fast risetime, with
harmonics well into the gigahertz region, so the small inductance of
the ground wire will have a significant impedance for this initial
fast spark current impulse, causing short high voltage spikes to
appear on the electrode, which are then conducted down the dowel. The
fact that these impulses are short may also be significant, as the
capacitance of the dowel will appear as increased conductivity of
these high frequencies - a rod that may appear insulating at DC could
well capacitively couple HF impulses - imagine lots of isolated
'drops' of water content - although insulated from each other at DC,
the inter-drop capacitance could appear as some conductivity at very
high frequencies.


On Sun, 09 Sep 2001 19:50:20 -0600, you wrote:

>Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Hollmike-at-aol-dot-com>
>
>Hi Richard, 
>    I have heard people mention this, but I don't think it actually absorbs 
>water significantly except perhaps on the surface.  If it actually absorbed 
>water, I doubt it would be very useful for plumbing purposes or the water 
>would 'bleed' through the pipes after a while.  Water does not bead up and 
>roll off pvc as it does with, say, teflon, so it probably is hydrophillic to 
>some extent.  It might not hurt to put a 'Jesus stick' under a heat lamp for 
>a while and then give it a coat of insulating varnish(or similar) to prevent 
>any moisture from collecting on the surface.  Assuming the ground connection 
>is reliable, the resistance of any water on the surface(assuming no salt is 
>present which should be the case) would be very high and the current would go 
>to ground throught the metal conductor rather that conducting down the pipe. 
>  I don't use such a device myself.  If I wish to draw an arc to ground, I 
>would set up some kind of stand to support the grounded 'target' and be away 
>from it when operating a coil.   I once got just a hair too close to my 8 
>inch coil and the output flashed up my arm.   Fortunately I was no where near 
>grounded(second floor of my apt with carpeting and luckily no outlets or 
>wiring in the walls very nearby), so I did not suffer any injury, but I did 
>get a warm sensation from it and could 'feel' the current travel over the 
>skin on my arm.  As I said, I think I was lucky and provided a high 
>resistance path to ground,  and was a few feet beyond the end of the visible 
>streamers so the air was not as conductive as it is with the ionized air of 
>the streamers.  It was a good lesson for me to be more careful and stay a bit 
>further away from my coil when operating it.   
>Learned and lived, 
>Mike 
>
>
>
>>
>> Isn't PVC hydrophilic?  I'm not a plastics guy though.  Maybe some one can 
>> fill 
>> us in.  Doesn't current path favor dielectric interfaces? 
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