arc fault calculation

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anbm

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Most of the time, around 10% of bus result from arc fault calculation (for incident energy) are more than 40 cal/cm2 which is more than category 4 from NFPA-70E table. Then, what type of cloth or protection should the service persons wear to service the elec. gears re replace breakers? NFPA-70E does not address this. It is strange!
 
Arc flash

Arc flash

anbm said:
Most of the time, around 10% of bus result from arc fault calculation (for incident energy) are more than 40 cal/cm2 which is more than category 4 from NFPA-70E table. Then, what type of cloth or protection should the service persons wear to service the elec. gears re replace breakers? NFPA-70E does not address this. It is strange!
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There is no protection for a rating above 4 due to explosive energy involved. Typically, I'll design the main breaker with a remote pushbutton for an instantaneous trip setting during a short circuit condition. It's also good practice to turn the power off upstream of any work at a Category 4 location.
 
The upstream of main gear is power utility xfmr, it's a pain to ask them to shut down every time. EPO for main CB maybe an option but not very often used/designed.
 
Dwight was not talking about an EPO (Emergency Power Off). Rather, he was talking about what some manufacturers call a "maintenance mode." You throw a switch or push a button that is located on the board, but that does not in itself constitute an action that risks an arc flash event. The switch or button enables the instantaneous trip feature of the main breaker, without actually opening the breaker. Under normal operation, the instantaneous trip is disabled, in order to force the main breaker to stay closed longer during a fault event, and allow a downstream breaker to trip first. This is the selective coordination notion that is required in some installations. By enabling the instantaneous trip, a fault will cause the main breaker to trip earlier, and that in turn would reduce the amount of arc flash energy that could be released. So you are taking a risk of losing the main breaker on a minor fault during the short time period that maintenance is being performed on the gear. If you install this "maintenance mode" feature, you can have the arc flash calculation revised, and that will probably reduce the required level of PPE.
 
You have any manufacturer cut-sheets, diagram, literature describing about this switch/"maintenance mode" feature? Thank!
 
charlie b said:
By enabling the instantaneous trip, a fault will cause the main breaker to trip earlier, and that in turn would reduce the amount of arc flash energy that could be released. So you are taking a risk of losing the main breaker on a minor fault during the short time period that maintenance is being performed on the gear. If you install this "maintenance mode" feature, you can have the arc flash calculation revised, and that will probably reduce the required level of PPE.
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It is extremely unlikely that a maintenance switch will reduce the AFIE at the breaker tripped by that switch.

Protective devices protect downstream locations not themselves.

The OP is inferring that his location is the service entrance equipment, in which case there are very few options available to reduce the AFIE at that equipment, and a maintenance switch is probably not one of them. His best option may be to provide a remote main device upstream of his service equipment, this would move the >40 cal/cm^2 to a different location, but it might allow interfacing with the remaining equipment.
 
I understood the question to involve the service board, but not the main breaker on that board. If you need to replace that breaker, there may be no option other than to get the utility to remove power. My intended message was that having a maintenance mode on the main breaker might allow work on the other breakers with a reduced level of PPE.
 
anbm said:
Most of the time, around 10% of bus result from arc fault calculation (for incident energy) are more than 40 cal/cm2 which is more than category 4 from NFPA-70E table. Then, what type of cloth or protection should the service persons wear to service the elec. gears re replace breakers? NFPA-70E does not address this. It is strange!
Click to expand...

I found this equipment that will protect a person vs 40 cal/cm^2 and up to 100 or even higher.


M1A1_abrams_tank_5.jpg



Arc Flashes cause vaporized/molten copper to be exploded towards you, the new anti-tank rounds do this exact thing.

http://www.youtube.com/watch?v=W6Im7PLduwc

Is a good example;
 
Have you seen the new GE arc vault protection gear it uses plasma to keep the arc inside a compartment .

It redirects by using high freq plasma there a video on U - tube go to GE ARC VAULT PROTECTION
 
ohmhead said:
Have you seen the new GE arc vault protection gear it uses plasma to keep the arc inside a compartment .

It redirects by using high freq plasma there a video on U - tube go to GE ARC VAULT PROTECTION
Click to expand...


I also read about this when an arc flash happens, it forces it to arc in this enclosed chamber that can be replaced. It was very cool but i dont think it was cheap.


** Edit

found it~

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

http://www.geindustrial.com/publibrary/checkout/ArcAbsorber?TNR=White%20Papers|ArcAbsorber|generic
 
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I talked with a fellow at GE and they have not installed but a few like two or three but its mostly installed in there own company owned plants its still in the new stage of bugs and seeing what problems they will have great inventive stuff but i know ill never get one to install in my time .

Take care i like seeing stuff thats new and electrical thought i pass it on .
 
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