[Sneap] sparking problem

[David Weisser]

Hi Tom,

The chain motors in the 14UD do not have filters.  The tank wall feed
throughs use spiral steel conduit inside the tank and from the tank wall
feed throughs to a connection box outside the tank.  There is no evidence of
spark damage to equipment inside or outside the tank associated with the
wiring.  This may be due to good luck in the routes that the conduit takes.

On at least one occasion, during a spark, I have seen a flash outside the
tank from one nominally grounded point to another.  Many labs do report
damage to external equipment.  We have put some effort into spark protecting
and grounding external vacuum gauges for example that used to fail and now
don't. We put grounded grids on vacuum gauge inputs and grounded shielding
on the gauge head to electronics cables.

There may  be a case for using steel rather than copper conduit since steel
will shield against magnetic energy in the sparks. Spark energy will radiate
around the filters unless the cable either side of the filter is an
adequate, seamless shield. One should use seamless steel conduit rather than
spiral.

Good Luck,

David

********************************************
D.C. Weisser
Nuclear Physics Department
Research School of Physical Sciences and Engineering
Australian National University
Canberra A.C.T. 0200
AUSTRALIA

Tel:    + 61 (0)2 6125 2080
Fax:    + 61 (0)2 6125 0748
Mobile: + 61 (0)414 249 209

david.weisser at anu.edu.au

  -----Original Message-----
  From: sneap-bounces at tunl.duke.edu [mailto:sneap-bounces at tunl.duke.edu]On
Behalf Of Miller, Thomas Edward
  Sent: Monday, 2 February 2009 12:35 AM
  To: sneap at tunl.duke.edu
  Subject: [Sneap] sparking problem


  SNEAPERs:



  I need your advice. For our 2 drive motors inside the tank we have PI
filters inside a metal box in series with the 2 motors. Connections from the
tank feedthrus are made with copper conduit to the box and then to the
motor. It was found that spark damage inside the copper conduit between the
wires and the copper conduit had damaged the wires that are between the
motor and PI filter box. What was done was the PI filter box was mounted
outside the tank and the conduit connecting both the PI filter box to the
tank feedthrus and the tank feedthrus to the motors was replaced with
plastic conduit. What this did was bring the spark energy outside the tank
where it can now damage equipment outside the tank.



  What is your recommended solution, i.e. how have you guys done it?



  I would like to have a better robust filtering for the motors on the
inside to prevent the spark energy from getting out of the tank and a better
conduit system. Seems like spark energy is traveling thru the motor 208 VAC
wires and needs to be removed right at the motor. Any help would be great.



  Thank you. Cheers!!!!



    Tom Miller

    Purdue University

    millerte at purdue.edu
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