[TCML] Spark Length(s): an anecdote

[Dave Pierson]

While the spark is OT, i believe the observation is apropos, re voltage/length/current
discussions.  I am one of the species called railfan, and was awaiting a train to
Boston, from New Haven.  The line, at the time, was powered by 12.KVAC/60 Hz
at GeeidunnohundredsAmps.  It was evening.  On an adjacent platform an EMU set was parked,
which caught my eye.  Normally the pantograph (Same function as trolley pole) remains up,
by spring pressure.  'certain faults', when detected, will cause the pan to self lower.
Some additional fault was not latching this pan down, so the sequence went:

  Pan UP.
   (fault detected)
   (Pan lowering initiated)
  Initial spark of about an inch.
  Spark then Stretched, as the pan lowered, to maybe 12-18".
   (I was a distance away.)
  Spark extinguished.
   (a different fault allows pan to rise and repeat until bored.)

  Thus, analagous to the case of a Jacobs Ladder, the existence of a spark
  at short distance allowed the path length to stretch considerable.

  Current involved unknown, I'd guess a few 10s of amps.  The 100s Amps alluded
  to above were what was _available_ and _drawn_ to move a train.

  best
 dwp