[TCML] Thumping Water Pipes

[Dave Leddon <dave@xxxxxxxxxx>]

I recently implemented software in my drsstc controller which permits 
the coil to be fired in a single burst varying from 100 to 1000 
milliseconds in duration.  In operation I noticed an thud following 
each burst occurring somewhere in the garage.  When I placed my hand 
on the copper water pipe feeding the water heater, the thump could be 
clearly felt every time the coil fired.  The discharge from the coil 
was striking a ground pole which was connected to a ground rod driven 
through the cement floor about one foot from where the water supply 
exits the ground and enters the garage.  When I grounded the strike 
pole to a different ground rod on the opposite side of the garage, 
the effect was greatly diminished, so I'm guessing that current 
passing through the pipe creates a magnetic pulse which reacts to the 
earths magnetic field but I thought that I would ask the experts for 
a more definitive answer.

Dave
Pleasanton, ca

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