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Safety--NFPA70E and Flashover Clearance Info



Original poster: David Sharpe <sccr4us-at-erols-dot-com> 

List

At work we've started (US) NFPA70E training for qualified electrical
personnel (i.e Electricians, Ttechnicians, Electrical Engineers).
NFPA70E
covers "Flash/Arc, Electrical Explosion" events, and proper personal
protective equipment (PPE), approach distances, proper tools,
equipment
procedures, etc.

These events can in fact happen with TC's, especially high power
machines.
Circuit Breakers can and do fail, and have led to deaths, panelboard
blowup, building fires, and other such calamities.  The  powerful
takeways in reading about electrical deaths and injuries is they tend
to fall into the following categories:
-  Inadequate training for task at hand
-  Improper or defective tools for environment (voltages worked on)
-  Domino failures caused by a failure in one piece causing a much
     larger blowup/fire upstream closer to utility feed.
-  Insufficient knowledge of site conditions (does conduit have
     energized wires, where are panels fed from, prints not up to date,
etc.).
-  Worker complacency ("I've worked 10 years and never been hurt"
     syndrome).

It is not meant to be, but some of the OSHA reports read like
something
out of "Oliver and Hardy" or "Dumb and Dumber".  It really hard to
fathom how someone could make a series of "no-common-sense"
decisions that lead to their demise...

In doing research on this topic, suggest "Googling"
- "Electrical Explosion"
- "NFPA 70E"
- "Flash/Arc"

Also the below link has a very good table of flashover clearance in
air
of various voltages up to 262kV, useful for designing clearances in HV

machines, since dimensions appear "reasonable" for dry sheltered
space.
Provided by the IAW union.

  http://www.uaw-dot-org/publications/skill/02/spring/spring02_7.html

Particularly newbies should read and re-read the Safety FAQ on Pupman
and read several of the incidents listed in links above.  They are
gruesome
and make several clear points:
1.  Your first mistake with HV could very well be your last.
2.  Make sure your tools and meters (as VOM's) are in good working
      order.  Many people have died because a VOM was defective and
      the victim assumed the power was off (rather then a bad meter).
3.  Never be complacent around HV, reread rule one above.
4.  _Learn from someone else's mistake, it very well could save your
life_!

Best Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA