Re: Definitions of High Voltage

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Dave,

On 3 Oct 2002, at 8:06, Tesla list wrote:

> Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<davep-at-quik-dot-com>
> 
> >> As per North's paper (High Voltage Insulation, pg1), any
> 
> >> voltage below approximately 340V will not discharge through
> >> air, regardless of spacing or barometric pressure 
> > what about 120 VAC?
> 
> 	cf below.
> 
> > ever unplug something while its still on?
> 
> 	Yep.
> 
> > Those are the same sparks you get from 12kV...
> 
> 	They are subtly different.  A voltage that will
> 	not jump across a gap 'by itself' will cheerfully
> 	maintain an arc/spark IF THE CURRENT IS FIRST FLOWING.
> 	Thus, if current is flowing in the 120V circuit
> 	it will spark a bit if disconnected hot.
> 	This is especially true of inductive loads.
> 
> 	True Story:
> 	I was at NH, Connecticut, waiting for a train.
> 	NH has electrified service to NYC, at 11 (or is it
> 	12.5) KV.  One of the cars had a defect, kept
> 	dropping the pan (contact) to the overhead.  12kv
> 	will spark over, about half an inch (varying with
> 	electrode shape, etc, etc....)  But.  AS the pan
> 	dropped, slowly drawing out the arc, it would stretch
> 	the arc to 2 feet or so, since the arc was started
> 	with current flowing.

I have drawn an arc out nearly a foot using an arc welder which has 
an open circuit output voltage of 40 or so. The current does the job.

Regards,
Malcolm