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Author Topic: Arc Flash Safety  (Read 12132 times)

Stephen Swaffer

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Arc Flash Safety
« on: December 23, 2013, 04:55:07 pm »

Mike, I agree with you about arc flash safety-I hope you can get techs to  understand the importance of taking precautions.  Around here, it seems like even electricians aren't concerned about arc flash.  Having worked in a facility that had the arc flash studies done and used the gear, I would think a long sleeve cotton shirt, leather gloves, safety glasses and hearing protection would serve most techs well.  Those are inexpensive safety precautions to implement.  Of course, if you are working on a 480 V panel or greater than 200 Amp you definitely need to find out what is appropriate or find someone who does know.

I know electricians are "expensive" and I like to do things myself, too, but often much of the cost difference  between me doing a project and a "do-it-your-selfer" is the cost of the materials I use to do it right vs taking a short cut.  I would guess that most electricians hourly rate is comparable to what sound/lighting techs charge-and in any event is certainly less than ER doctors and burn units charge.  I  have made major equipment decisions based on the thought that while another route may be cheaper in the short run, one trip to the ER or a few weeks of missed work might be far costlier!  It might be wise to get to know an electrician you use for larger projects (or for tie-ins  so that you have someone that the legal people would view as qualified) that would be happy to give advice on smaller projects-in order to keep his customer healthy.
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Steve Swaffer

Mike Sokol

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Re: Arc Flash Safety
« Reply #1 on: December 23, 2013, 06:07:49 pm »

Having worked in a facility that had the arc flash studies done and used the gear, I would think a long sleeve cotton shirt, leather gloves, safety glasses and hearing protection would serve most techs well.  Those are inexpensive safety precautions to implement.

Yes, I would agree that your list could be workable. Cotton shirts are way better than polyester which melts into your skin from an arc flash (no kidding). Safety glasses are always an excellent idea, but most companies won't rate glasses for arc flash, insisting on face shields instead. And lightweight gloves would work since power under 600 volts is considered "low-voltage". I also have 3M sending me a pair of their ARC Plug earplugs which allows for normal conversation, but shuts out impulse noises and explosion decibels. See http://tinyurl.com/lvj2v57

But we'll have to convince OSHA that these simple precautions are sufficient. As I'm sure you all have done (as have I) we often tie in camlocks with no more protection than a layer of sweat and a t-shirt. As you know from your own arc flash training, the type of PPE (Personal Protective Equipment) is dependent on energy levels. So the total fault currents available on various sound and lighting distros would need to be reviewed. However, I personally feel that anything would be an improvement over the lack of any protection at all.

And in the interest of complete disclosure, I lived through an arc flash less than 2 ft from my face in 1970 when I was about 15 years old and helping a master electrician tie in some new circuit breakers in my parents' house. He was an electrical instructor at a tech school and I was doing an electrician apprentice program. He insisted I have on my safety glasses and long-sleeved cotton shirt, so he was ahead of his time, I think. While horsing a ground wire around the side of the panel using a pair of insulated electrician's pliers, I nicked the insulation on the 100-amp service ahead of the main fuses. What happened next can only be described as a bomb going off in my hands. It vaporized about 3 ft of 14 gauge wire in a ball of light that sounded like a shotgun blast. I was standing on a wooden chair with my one hand still in the box, and my teacher was telling me to stand very still.

I saw a much bigger one later involving a 600-amp/480-volt feeder, but lucky for me I was about 100 yards away from it. More on that arc flash later. 
« Last Edit: December 23, 2013, 06:47:48 pm by Mike Sokol »
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Mike Sokol
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Lyle Williams

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Re: Arc Flash Safety
« Reply #2 on: December 23, 2013, 11:40:46 pm »

I saw the feeder for about 5000 houses shorted out one night.  I was about 100m away.  It lasted about a second and a half and seemed brighter than the sun. 
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Jonathan Johnson

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Re: Arc Flash Safety
« Reply #3 on: December 24, 2013, 12:30:20 am »

I have no arc flash training, but I am aware of it.

One of the industrial facilities where I provide network support has a bank of large enclosed switches (the kind with a swinging door and a lever on the side).

Next to this bank is a sign reminding operators to do the following (in addition to wearing PPE) when actuating a switch:
  • Turn your face away from the panel
  • Stand to the side opposite the hinge
The reason for the first is obvious. The reason for the second -- I assume -- is to protect the operator from the door being violently flung open from an arc flash explosion. It would also protect the operator from some of the arc flash.
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Stop confusing the issue with facts and logic!

Mike Sokol

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Re: Arc Flash Safety
« Reply #4 on: December 25, 2013, 03:38:06 pm »

I saw the feeder for about 5000 houses shorted out one night.  I was about 100m away.  It lasted about a second and a half and seemed brighter than the sun.

I love this one. Not technically an "arc flash" but certainly a really big arc...

http://www.youtube.com/watch?v=NQQMK1Rvq0A

Just added a compilation video including the one above. My favorite quote is "If it blows up, get ready to hit the ground".

http://www.youtube.com/watch?v=_2LpCdhuOyQ
« Last Edit: December 25, 2013, 03:44:02 pm by Mike Sokol »
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Stephen Swaffer

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Re: Arc Flash Safety
« Reply #5 on: December 29, 2013, 04:46:41 pm »

As far as arc flash safety and the entertainment industry is concerned, it might make more sense to address mitigation of the hazard versus using the proper PPE?

The arc flash safety emphasis has been industry.  Most industrial facilities have a large number of panels that are relatively infrequently accessed so taking PPE with you makes economic sense.  I would surmise that most entertainment venues would have a handful of panels allocated to tie-ins from touring lighting and audio contractors-and those would be accessed frequently so perhaps mitigating the hazard would make more sense.

I saw a video by Cooper Bussman a few years ago-and they have white papers on the subject (no doubt driven by the desire to sell fuses!) regarding the advantages of their Low Peak fuse designs in controlling arc flash.

Fuses have been given a bad rap by the Edison fuse-which being available in sizes to 30 A in the same form factohas resulted in a very high percentage of systems using it being overfused.  But the fact is, they are more reliable and can react quicker protecting both personnel and equipment.

Obviously, losing a fuse during a performance is more of a problem than tripping a breaker, but if carefully thought out and designed, fuses could be used to provide safety with a smaller breaker providing overload protection-much like what is down with motors and overloads.   
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Steve Swaffer

Tim McCulloch

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Re: Arc Flash Safety
« Reply #6 on: December 29, 2013, 05:33:47 pm »

As far as arc flash safety and the entertainment industry is concerned, it might make more sense to address mitigation of the hazard versus using the proper PPE?

The arc flash safety emphasis has been industry.  Most industrial facilities have a large number of panels that are relatively infrequently accessed so taking PPE with you makes economic sense.  I would surmise that most entertainment venues would have a handful of panels allocated to tie-ins from touring lighting and audio contractors-and those would be accessed frequently so perhaps mitigating the hazard would make more sense.

I saw a video by Cooper Bussman a few years ago-and they have white papers on the subject (no doubt driven by the desire to sell fuses!) regarding the advantages of their Low Peak fuse designs in controlling arc flash.

Fuses have been given a bad rap by the Edison fuse-which being available in sizes to 30 A in the same form factohas resulted in a very high percentage of systems using it being overfused.  But the fact is, they are more reliable and can react quicker protecting both personnel and equipment.

Obviously, losing a fuse during a performance is more of a problem than tripping a breaker, but if carefully thought out and designed, fuses could be used to provide safety with a smaller breaker providing overload protection-much like what is down with motors and overloads.

I'm an arena sparky.  I'm one of the folks that does your road show power when it comes to our PAC, arena(s) or couple other places.

None of the major venues have "live" boxes; i.e. the disconnect switch is tagged/locked out at its master breaker or the physical design has shunt-trip and connector chamber switches that de-energize the entire panel when opened.  Almost all of the newer venues have CamLock and/or Posi-Lock connections with additional wire tails capability.  Most of the tie-ins (not direct Cam connections) I do these days are with generators or in a couple of older theaters.

I don't work in live panels.  Ever.  That shit kills people and burns down buildings.  One of the things that defines "qualified" is knowing when one is NOT...

Don't take the above as an attempt to minimize PPE, it's not...  After working in production for nearly 30 years and as a show electrician for 14 years, I've seen all kinds of dodgy stuff.  What I've observed, though, is that if I need the level of PPE to deal with a potential arc flash the situation is above my pay grade.  Mitigation of hazard, beginning at the design stage, is the best practice IMHO.
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Lyle Williams

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Re: Arc Flash Safety
« Reply #7 on: December 29, 2013, 08:20:47 pm »

I am not a sparky, but my day-job system uses a lot of electricity.  Around a hundred gigawatt hours per annum.  Downtime costs serious money.  Really serious money.

How much live power work do we have done?  Zero.  Zilch.  Live power work is for cowboys.
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Stephen Swaffer

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Re: Arc Flash Safety
« Reply #8 on: December 29, 2013, 11:06:09 pm »

Not to be argumentative, but, Lyle, would you have every electrician that does any wiring upgrades to a home call the utility and cut the power to the home at the transformer?  That is the only way to get a de-energized system in a home-or really in any occupancy ultimately you can't keep de-energizing upstream. (Even shutting off the main leaves energized conductors in the panel.)  And troubleshooting can be very challenging when all power is disconnected.

Part of LOTO is verification-which unless indicators have been designed into a system requires use of PPE appropriate for a live situation until verification is complete.  Please don't tell me I am the only one that has ever shut off the wrong breaker knowing I had the right one? 

A typical home arc welder runs at 30-40 volts and 60-100 amps-plenty of arc for a burn, and indeed 70E calls for "PPE" for anything above 50 volts or so.  I doubt you would consider that above your pay grade?  PPE doesn't have to mean a spacesuit-it might be that the items I mentioned in the OP are enough-they are inexpensive and simple IF we think about them.

I am not arguing for making life difficult-we all tend to get comfortable with things and that is when people get hurt.
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Steve Swaffer

Lyle Williams

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Re: Arc Flash Safety
« Reply #9 on: December 29, 2013, 11:53:40 pm »

Residential power down here has a unscrewable (with an insulated pole) fuses on the ceramic insulators where the cable enters the house, breakers in the outside meter panel, and individual circuit breakers for each circuit on an inside panel.  If something needs to be rewired, turn it off, lock it out, short it out, ... 

Obviously problems need to be recreated to find the fault.  I'm not suggesting that nobody ever measures live power.


In an industrial setting, the need to work on live and loaded circuits is something that comes from poor planning.  If the site isn't built to be concurrently maintainable then that is a design/management problem.  We don't ask our sparkys to put their lives on the line because someone made a cheap design choice five years earlier.  If a whole site needs to be shut down for electrical works then we make sure we make use of the outage to install enough additional panels/breakers/switching/etc that next time less needs to go offline.

I was not suggesting people don't use PPE.  Far from it, I was suggesting people work out how to reduce risks even further.
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