Arc Flash

[newt]

I had an arc flash 120/208 200 amp 3 phase in a meter can it was a feeder tap off a 800 amp disconnect 500 kva pad mount 4-5 percent impedance. service conductors parallel 500 mcm cooper 100 f tin length 10 ft feeder tap to meter can. transformer high side 12470 40 amp fuse no clf just outside substation fence available fault current high side was 5000 amp l-n. The fault occurred when I pulled meter burnt a hole in my keeper and my rubber glove nothing tripped it took a substation crew to trip breaker( inst trip blocked) to clear fault 10 min later. Caught building on fire now I have to meet with safety. My safety manual states 8 cal is all need if it is higher I will be told. Can this arc flash be calculated and isn't over 8 Cal?

 

[wbdvt]

There are several ways to look at this. The problem with 208V arc flash hazards is that the IEEE 1584-2002 standard was only able to sustain an arc at 208V in one test specimen. That led to the exception for 208V services supplied by transformers less than 125kVA.

Since this is a meter can, this would most likely fall under NESC rules used by utilities. For a 208V self contained meter, the clothing system required is 4 cal/cm2. There is a footnote to that which states "Industry testing on this equipment by two separate major utilities and a research institute has demonstrated that voltages 50V to 250V will not sustain arcs for more than 2 cycles, therby limiting exposure to less than 4 cal/cm2."

Now, doing a quick model calculation on the system you describe with some assumptions and using 2 cycles, the incident energy is 0.6 cal/cm2.

What I find interesting is that you state a hole was burnt thru the keeper and rubber glove. Arcwear has done testing on leather keepers as well as rubber gloves. What they found is that almost all the rubber gloves, in combination with the keepers, had a ATPV of 40.

 

[newt]

The meter room is only 200 ft from the substation so im guessing fault current was high and nothing tripped high side or secondary the fault actually welded the customers main disconnect closed. This fault continued for minutes not cycles.

 

[newt]

The fault burnt a 2 inch hole in a breaker enclosure that was 2ft away, the transformer was a 500 kva so would that increase arc to a level that is that catastrophic

 

[wbdvt]

true, so more information is needed to accurately model the system to determine what the incident energy actually was.

 

[newt]

Thanks for your help

 

[kwired]

I had an arc flash 120/208 200 amp 3 phase in a meter can it was a feeder tap off a 800 amp disconnect 500 kva pad mount 4-5 percent impedance. service conductors parallel 500 mcm cooper 100 f tin length 10 ft feeder tap to meter can. transformer high side 12470 40 amp fuse no clf just outside substation fence available fault current high side was 5000 amp l-n. The fault occurred when I pulled meter burnt a hole in my keeper and my rubber glove nothing tripped it took a substation crew to trip breaker( inst trip blocked) to clear fault 10 min later. Caught building on fire now I have to meet with safety. My safety manual states 8 cal is all need if it is higher I will be told. Can this arc flash be calculated and isn't over 8 Cal?

Had to read this a couple times, but eventually figured you must have been pulling a 200 amp meter (maybe for separate tenant in multiple occupancy application?). Still don't know why if there was a 800 amp disconnect ahead of this why there wouldn't have been an overcurrent device associated with it that likely shouldn't have held for 10 minutes? If not a bolted fault, 208 volts just can't sustain an arc for very long at all without feeding more conductive material into the arc like is done when "welding".

 

[newt]

Pictures of actual incident

Pictures of actual incident

Aftermath

 

[newt]

Burnt Glove Pic

Burnt Glove Pic

Leather glove with rubber glove underneath.

 

[peter d]

A wirebrush and some spray paint and that will be as good as new.

 

[big john]

...What I find interesting is that you state a hole was burnt thru the keeper and rubber glove. Arcwear has done testing on leather keepers as well as rubber gloves. What they found is that almost all the rubber gloves, in combination with the keepers, had a ATPV of 40.

Definitely, I've always heard that leathers and rubbers offered fantastic flash protection, even though they are admittedly not rated for it.

 

[newt]

im thinking its over 8 cal

 

[newt]

this was a feeder tap

 

[dpeter]

That looks like a lot of damage... Hope you escaped intact.

 

[jim dungar]

Definitely, I've always heard that leathers and rubbers offered fantastic flash protection...

They do, but remember that even appropriate Arc Flash PPE does not ensure no injury.