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What is the flash of arc flash?

6K views 26 replies 13 participants last post by  Golden Arc 
#1 ·
I would like to say that I have always respected electricity. And that I really didn't know what arc flash was, still really don't get it though. But I can say I am definitely less likely to do any live work since that other thread got me looking into arc flash.

The videos where the flash looks like a ball of flame.... what is the flame? is it the bus bar/breaker vaporizing in a flaming cloud of well metal?

I also understand that arc flash is high current with a low impedance path to ground. I think.
I am in second period schooling, so some of this is still a bit beyond the scope of what I currently know.

Does arc flash need the cross phase short to happen? Like could it happen putting a single phase breaker in?


I can officially say that I no longer feel "safe" doing a lot of stuff live. I will still change a light bulb live though. But I most certainly do not think adding a 3 phase 600v breaker in a live panel is "safe" even with insulated tools anymore.
 
#2 ·
What is Arc Flash?

Arc flash is a short circuit through air that flashes over from one exposed live conductor to another conductor or to ground. Arc flash incidents are common and costly, and the frequency of reported accidents is increasing. This is why arc flash has become a very hot topic within OSHA and the safety industry overall.



This may help as well


What is Arc Flash?
 
#3 · (Edited)
Well Jeffooo got a good one for you once we had a 5000 amp 480 4 wy service and were shut down main breaker was off , this was during new construction project engineer added a new sub feeder into this switchboard another extra pulled in wire added new brk .

We got done had our inspection closed up the switchboard we went to turn the 5000 amp main brk back on when i pumped up the main and then pushed the closed button a loud bang and flash a flame came out the front of that breaker it burnt my arm nothing bad just a little .

Heres why it happen our shunt trip switches were located on a control panel in a plant security control room .
There was 7 switches well someone accidentially turned that switch on so the breaker was in shunt when i turned it on and we did not have all the loads down stream turned off .
That space between contacts had a hell of a current passing and well it sounded like lighting struck i smoked a little bit but was fine . It never made full contact but got close enough to conduct . To me its the air gap conducting yes air will conduct at a distance between two points of potential !
We had to replace that breaker it was burnt and never would close again . Take care be safe
 
#4 ·
Well Jeffooo got a good one for you once we had a 5000 amp 480 4 wy service and were shut down main breaker was off , this was during new construction project engineer added a new sub feeder into this switchboard another extra pulled in wire added new brk .

We got done had our inspection closed up the switchboard we went to turn the 5000 amp main brk back on when i pumped up the main and then pushed the closed button a loud bang and flash a flame came out the front of that breaker it burnt my arm nothing bad just a little .
What? No PPE? You know better. Sounds like you need your own remote operator with all the high energy work and njuries you have had.

We had to replace that breaker it was burnt and never would close again . Take care be safe
I am 100% certian I can fix that breaker like it was brand new.
 
#5 ·
I would like to say that I have always respected electricity. And that I really didn't know what arc flash was, still really don't get it though. But I can say I am definitely less likely to do any live work since that other thread got me looking into arc flash.

The videos where the flash looks like a ball of flame.... what is the flame? is it the bus bar/breaker vaporizing in a flaming cloud of well metal?
A combonation of Ionized air and vaporized copper, temperatures acan be around 36,000F. Steel melts around 1/20th of that just for a reference.

I also understand that arc flash is high current with a low impedance path to ground. I think.
High current is a relative term. The arc can be phase to phase, phase to ground, or 3 phase. Most start out as phase to ground but that ionized air you see allows most to becomes 3 phase arcs. The current level values can vary widely and are different of different voltage systems and systems with different available fault currents.

The actual arcing currents will be somewhere between the max availabel fault current and the minumum current that the arc can be self sustaining.

Does arc flash need the cross phase short to happen? Like could it happen putting a single phase breaker in?
No and yes

I can officially say that I no longer feel "safe" doing a lot of stuff live. I will still change a light bulb live though. But I most certainly do not think adding a 3 phase 600v breaker in a live panel is "safe" even with insulated tools anymore.
If you want to learn more about arc flash I would go here.
http://www.arcflashforum.com/index.php
Nothing against this forum but it is not really a good source for arc flash info and that is not the primary intent of it. Not to mention following NFPA 70E around here seems to be an unpopular choice by many members.
 
#12 ·
A combonation of Ionized air and vaporized copper, temperatures acan be around 36,000F. Steel melts around 1/20th of that just for a reference.

High current is a relative term. The arc can be phase to phase, phase to ground, or 3 phase. Most start out as phase to ground but that ionized air you see allows most to becomes 3 phase arcs. The current level values can vary widely and are different of different voltage systems and systems with different available fault currents.

The actual arcing currents will be somewhere between the max availabel fault current and the minumum current that the arc can be self sustaining.

No and yes

If you want to learn more about arc flash I would go here.
http://www.arcflashforum.com/index.php
Nothing against this forum but it is not really a good source for arc flash info and that is not the primary intent of it. Not to mention following NFPA 70E around here seems to be an unpopular choice by many members.
I will have to read through that forum here, some interesting stuff on first look.
I have no yet learned how to calculate the max fault current available, only what factors lead to it. So that whole thing doesnt make complete sense to me yet.

I just noticed the gloves I wear are nomex though, although I doubt they are rated for much.
I also have nomex long underwear, but wear my helly hansen stuff more often. But I do wear a nomex 6cal long sleeve shirt most of the year. Although not sure how much it would help. I have a 6cal short sleeve shirt too, but dont wear it as often, but will wear both when its that in between temp out.

No. I was asking Jeff how he was comfortable in 600 V panels.
From day one it is what I have worked with the most, and was shown everything on. I am more comfortable in a siemens 347/600 panel with bolt in breakers then I am in a 120/240 panel.
 
#7 ·
How could you ever be comfortable in a 600 V panel? My knees get weak thinking about it. It is at these levels that you don't really have to touch anything. It will come and get you if you are close enough. Not saying I wouldn't work it, just that it would be on my mind constantly..
 
#8 ·
Are you asking me about being comfortable the power was off ! The main breaker was OFF DURING THE WORK LOCKED OUT TAGGED OUT . we turned it back on after the work was done and all the covers were back on . we kinda do only distribution work 480 volts is not a issue now above 4160 i get real safe . Take care
 
#18 · (Edited)
#20 ·
Well Zog if you read SQ D recommended ppe protection in most cases it is to be worn .
http://ecatalog.squared.com/pubs/Electrical%20Distribution/Low%20Voltage%20Switchgear/PZ4/0100DB0804.pdf

But if the gear or switchboard has been installed and in service meaning energized and a shut down or turn on was needed no ppe is needed as the gear is ANSI rated per 70 e . KEY WORDS [ was hot] ! Read the attach document ? Best to yas
Of course I have read that same document before Nick, you know better than that. When Square D say "It is our position" it dosent mean that the 70E and OSHA requirements do not apply, it is a sales ploy, all the OEM's do it. They are saying that thiier gear should contain and arc flash with the covers on if ....folowed by a bunch of criteria a first year law student could use in any defense case.

Actually with new gear, they may be right, it may contain an arc flash with the doors on but it has not been tested, and the 70E can't cover all vintages and manufactures. the standard is confsing enough the way it is so it is generic and is designed to protect workers from new equipment, and rusted out old gear with vents on the doors too.

If it was this new Sq-D gear and you were burned from the flash with the doors closed as you said obviously the PDF you posted is wrong.
 
#19 · (Edited)
I always test and take proper precaution, I have never had any personal expierence with arc flash* (AC). But have been involved in cleaning many others screw ups. Some with death involved.

There is in my opinion NO reason for an arc flash incident if the electricians take proper precautions. There are some case with equipment issue but 99% of the cases I have been involved with were human error. And in each case the injured parties blamed the equipment (if they were able to talk).

*The one incident I had with burns was a battery exploding.
 
#21 ·
arc flash...dude...go to youtube and look up 480 three phase arc blast.
34000 degrees instantaneously. I think about it all the time. Guy working at the NIST in Colorado got blasted somehow by just leaning up against a panel in a service corridor. Must have been some unusual circumstances, but since hearing that story i never even so much as lean my hand up against any electrical equipment. Not worth it.
 
#22 · (Edited)
Well lets look at it in a new way maybe there instructions are faulty misleading in there guide to PPE to protect them from the legal incidental kinda cover all . Is one educated enough no is my answer !

My case it was years ago but i was not injured just a minor flame out nothing but a little hair snuffed off .
It maybe a general instruction on how or who does what even installing a AF sticker they send with equipment no normal everyday electrician ever installs these ! No one would ever ware PPE to turn on a breaker with cover on never in this trade .
Our workers go to a 10- hr OSHA and a 8 hr - First Aid program we do not deal with any other safety programs but have our companys safety program rule one we never work hot . But our service department will on special jobs .

Most small electrical contractors dont have the funds to have PPE and dont use it ever .
Bottom line if the breaker was not in shunt it would not have failed and if we shut down all down stream loads it would have been fine even in shunt .

We were giving a simple example of a flash for the op Jeffooo it turned out that now Jeffooo must ware a hot suit to turn on a breaker with the cover on .

Now he not only can not work it HOT !! But he must tell his boss he needs a Hot Suit to turn on the breaker according to ANSI 70 E and also all electricians are not doing there jobs in the usa correctly !

How many EC will comply ?
Do you think Jeff will have a job ?
We have lots of hot suits Zog but our company does lots of bigg jobs id say 90 % of the EC in America dont ?
Also some advise id like to give by giving a example of ones mistakes or experience encountered over the years i think the forum will benefit as we now have seen .



Take care Zog
 
#23 ·
arc flash

Zog, I know that you are knowledgable about arc flash...tell me if I am wrong. When you have either a phase to phase connection or a phase to ground connection, unintentionally, the conditions are set up as to release energy, and as it is released it starts creating it's own atmosphere of miniature molten parts of copper , other metals, and the like. The catastrophe feeds on itself for a time until it cannot further sustain itself.
 
#24 ·
Zog, I know that you are knowledgable about arc flash...tell me if I am wrong. When you have either a phase to phase connection or a phase to ground connection, unintentionally, the conditions are set up as to release energy,
That is more like a bolted fault, much higher fault currents than an arc flash but not much of an arc or heat produced. However, a bolted fault can develop into an arcing fault.

and as it is released it starts creating it's own atmosphere of miniature molten parts of copper , other metals, and the like.
Yep, an arc flash is current passing through air, very much like a lightning strike. When the electrical potential between 2 points is high enough and/or the resistance of the air pathway between those 2 points becomes low enough (Dust gets stirred up, high humidity, forgein materials, etc) the air becomes ionized and begins to throw off electrons, this allows a low resistance path between the 2 points and the arc flash ocurs. The arcing path itself is very conductive (Plasma cloud) and a simple phase to phsae or phsae to ground arc flash usually will develop into a 3 phase arcing fault.

The catastrophe feeds on itself for a time until it cannot further sustain itself.
Either cannot self sustain or gets cleared by an OCPD.
 
#26 ·
Carbon, steel, aluminum, copper, plastic (depending on the components at the point of the fault). A mixture of hot gasses and particles coming at you at incredible speed. There are many things that can and will get you, heat, flash, pressure of the fast moving event and even if you do not burn you may still inhale the gaseous mixture and damage your lungs and or be slammed into a wall.
 
#27 ·
Insulating the lenses on lay in lights?

We got some lay in lights for a kitchen we were doing, and the lens have bags of insulation in them like a sticky sponge trim strip that goes around the lens. When i asked someone about it they said its incase the bulbs shatter and get in the food.
 
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