NFPA 70E Training outcomes (Ref: Safety Training...)

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Original poster: Sparktron01-at-comcast-dot-net 


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I attended this training several weeks ago (2 days).  There were many 
videos of severe injuries and fatalities arising from "Arc Flash/ 
Electrical Explosions", and several videos of staged electrical explosions 
(up to 15kV -at- 5kA) that were frightening to say the least (see Bert 
Hickman's video of the substation catastrophic KABOOM to have a similar 
reality check).  The interesting take homes and statistics from this 
training are:

1.  80% of nationwide electrical fatalities involved qualified electrical 
personnel (i.e. they had multiple years experience in electrical trade).

2.  Many fatalities involved "gettting comfortable" in your job, and 
eventually leads to shortcuts being taken (complacency).  On HV gear this 
is an invitation for disaster.

3.  HV and high power LV equipment can have equipment failure, and if you 
are near it when it lets go, all bets are off unless you have PPE 
on.  Water expands from liquid to vapor 1700 times it's liquid 
volume.  Copper vapor / plasma expands 64,000 times (!!!!!) its original 
solid volume.  Under a high energy fault condition, this will result in a 
violent thermal explosion with molten debris, and electrical plasma being 
ejected at high velocity, with a time duration of 0.5 sec or less.  Impact 
energies can be suffciently high to shear 3/8" steel bolts.  Imagine 
several thermite grenades and sticks of dynamite going off in confined 
quarters simultaneously...

4.  Many folks have died by bad meters, meter leads, or making an 
ASSumption that the power was turned off and no back feed path existed.  If 
a DVM is not rated for class III (CB panelboard) service, and a high energy 
HV transient causes an arc over internal to meter; can result in a meter 
explosion.  The moral of the story is DO NOT risk your life using a $3.00 
Harbor Freight (or similar) DVM's, use an industrially rated meter if 
working on high power/energy circuits that may be live.  Also if you have 
to replace the meter fuse, replace it with the EXACT replacement, they are 
usually designed with higher then normal interrupting and voltage clearing 
rating (AFAIK Fluke uses 17kA / 1kV ceramic cartridge fuse in ammeter 
circuit as an example).

5.  Circuit breakers should be mechanically exercised ONCE A YEAR.  This 
was a revelation to me, but with our TC's of various flavors pounding our 
house panels, please take heed.  The CB mechanism can be uncalibrated by 
extended time running at 90-95% of breaker ampacity by internal 
heating.  This may preclude the breaker from operating at all.  If you 
operate the breaker and it does not "feel" right, or sounds "mushy" when 
the contacts open and close; REPLACE THE CB.  It is cheaper then replacing 
your house!

6.  Fuses are a much more reliable high energy interrupting means then 
CB's.  They are commercially available with interrupting ratings to 300kA, 
and low-peak fuses will clear a high energy fault in less then 1/4 cycle 
60Hz (4 millisecs).  Low peak fuses also dramatically limit arc/flash exposure.

7.  Use GFI's, they are lifesavers.

8.  Wear cotton clothing rather then synthetics when working around HV or 
high energy circuits, the synthetics when exposed to arc/flash can melt 
into the skin and cause severe 2nd and 3rd degree burns.

9.  Avoid working on HV circuits alone, use the "buddy" system.

Be safe out there...

Regards

Dave Sharpe TCBOR/HEAS, Chesterfield, VA. USA