iwire said:
NO WE DON'T KNOW THAT!
Your assuming all electricians get the same level of training you have.
WE DON'T!
I bet 80 to 90% of the licensed electricians in this country have never been to any training at all regarding PPE.
I have been to some classes but I worked for a large shop that had a Safety Director, very few electrical shops have that or any safety training or any real safety equipment.
ok. another long winded post:
show and tell.......
after spending some time snuggling up to google,
with some thoughts about all this, here's what i found....
to see the exact nature of the problem, go here:
http://www.easypower.com/arc_flash/arc_flash_videos.php
for a quick seat of the pants calculation on the energy released
in an arc fault situation, go here:
http://www.easypower.com/arc_flash/arc_flash_calculator.php
for some levels of protection, with pricing, go here:
http://www.70estore.com/HRC_level_4/
that little stupid arc fault sticker that is supposed to be on everything
including the bathroom door by now gives all the information you need
about how to protect yourself.
there are five factors that affect arc fault:
type of equipment
bolted fault current - depends on service type, and utility supply
working voltage
working distance
time to clear
let's say, for the sake of argument, that you are working in a MCC
pulling out a bucket. a little 30 amp bucket to feed
a 3 hp pump in a food packing plant. it's old gear, and pretty crusty.
you approach it with a left handed look out of your right eye, and
some caution. here is what your risk is....
the upstream supply is 45k bolted fault current
the voltage is 480
distance is 18"
it takes 1 second to clear the fault 'cause the clips
on the back of the bucket wouldn't come loose, and
the insulator fractured, dropping a chunk of metal across
a & b phase.
here's what the calculations say:
Results
Arc Boundary
over 30 feet
Incident Energy
113.3 cal/cm2
Clothing Class
Extreme Danger - Dangerous work hazard; Energized work prohibited
i mention this task for a simple reason... it's commonly done,
and most often without protective equipment. and it's something
where arc fault from a mechanical malfunction is a real possibility.
a 100 calorie suit is sturdy enough to stand up by itself. many of them
have forced ventilation into the hood to make it tolerable even
to wear them. not only have i never worn a 100 calorie suit, i've
never even SEEN one on a jobsite, and i've worked for public utilities
obsessed with safety. why is that?
couple reasons, in my opinion....
a suit like that is about $2,000
getting someone to wear it, short of threatening dismissal, is difficult.
so... what do you do?
shut the switchgear off.
at 113 calories there is no PPE sufficient to protect you.
but this is a common task, and i've seldom seen anyone shut down
a mcc to do it. including me. it's time to change that. last week i
had to snoodle some wires into an old piece of gear at a water bottling
plant. the gear was about 50 years old, a 240 delta MCC.
most of the deadfronts in the wireway were long gone, the bus was
open and exposed, and branch circuits and control wires were everywhere.
i looked at it, and here's what it looked like:
notice the exposed vertical and horizontal bus in back, and further along,
the field wiring was tie wrapped to the busbar for support.
here's roughly what the risk looks like:
Results
Arc Boundary
over 19 feet
Incident Energy
51.7 cal/cm2
Clothing Class
Extreme Danger - Dangerous work hazard; Energized work prohibited
what i was wearing amounted to 7 calories of protection. do the math.
it's time to do it differently.
randy
