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 Post subject: NFPA 70E 2012 DC Arc Flash - Direct Curent Arc Flash
PostPosted: Tue Jul 10, 2012 11:21 am 
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Joined: Tue Jul 10, 2012 11:18 am
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Hi,
Question related to NFPA 70E 2012 DC Arc Flash

Are the DC systems mandatory to do Arc Flash calculation and lablel or not?

if you could refere to the NFPA section that will be great.

Thank you for help.


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PostPosted: Thu Jul 12, 2012 6:10 am 
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Joined: Wed Jun 10, 2009 5:00 pm
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Location: Toronto
There are now specific requirements for arc-flash protection on dc systems. Also, many of the general safety requirements apply to both ac and dc systems. Please refer to the NFPA 70E 2012 sections:

D.8.1 Direct-Current Arc Flash Calculations
D.8.1.1 Maximum Power Method
D.8.1.2 Detailed Arcing Current and Energy Calculations Method

and this forum thread http://www.arcflashforum.com/threads/2332/

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Michael Furtak, C.E.T.
http://arcadvisor.com


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PostPosted: Thu Jul 12, 2012 7:20 am 
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Thank you very much for the information.


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PostPosted: Mon Jul 16, 2012 8:59 pm 
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Joined: Sun Sep 23, 2007 5:00 pm
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Location: Calgary, Alberta, Canada
You can use the Hazard/risk category Tables or complete DC incident energy analysis. The major power system software packages now all have DC incident energy formulas added.

This is a new topic and "learning" is required to complete the calculations for DC. Thankfully we don't have a lot of DC systems out there as compared to AC. Yes UPS Batteries, typically small systems and of course there are some larger DC system like trains, submarines, chemical processes, etc.

Regards;
Terry Becker, P.Eng.
Owner, ESPS Electrical Safety Program Solutions INC.
[url="http://www.esps.ca"]www.esps.ca[/url] / [url="http://www.arcflash-training.ca"]www.arcflash-training.ca[/url]


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PostPosted: Mon Jul 23, 2012 8:42 am 
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Joined: Thu May 31, 2012 6:27 am
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Location: Warrensburg, Missouri
We manufacture sealed lead acid batteries. Mainly used as communication UPS. 70aH and above. We charge the batteries in strings of 20-24. they are lined up on a conveyor table. They are interconnected with banana jack style jumper cables. The positive and negative leads are plugged in to the charging rectifier using Anderson connectors. We have rows and rows set up this way. About 700 rectifier circuits. I am concerned that we have no PPE in use by the operators who connect these up for charge and to disconnect them. Are there any other battery manufactuing plants that can provide some insite as to whether this is a valid problem or not?


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PostPosted: Mon Jul 23, 2012 10:42 am 
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Joined: Thu Feb 04, 2010 5:00 pm
Posts: 36
Location: Camp hill Pa
It is not uncommon to have UPS systems with batteries rated 1000 amperes and 600 volt DC. These cells are all generaly connected in series with bare copper bars, and then connected to a fused switch. The potential arc energy available at the battery, prior to the fuses, can be very great even if only a single cell is shorted, let alone the entire 300 cell string. This is why most DC systems have the positive and negative conductors in seperate conduits.

Trolley systems are often feed today with rectifiers at up to 1200 volt and amperages of a 1000 amperes and more. On one transit system, that I know of, the technicians use a 10 foot hot stike to operate the enclosed metal clad disconnect switches.

Some home off-grid PV systems often have 48 Volt batterys with 1000 Ampere Hour batteries. (generally the are sized to only discharge to a 50% level and supply power for 3 cloudy days.)

Total energy in a 2 volt 1000 Ampere hour cell is 2 kwH and in a short circuit can dissipate 1/2 that energyin an arc. wow, stand clear and/or run. One needs acid resisten clothing as well as flame resistent clothing. The life you save wil be your own. the battery can also explode. OSHA, I am sure probably has requirements on battery maintenance.

I knew one young EE, who disconected a battery when the igition system shorted out on his 1960 convair. After he realized what he did, he decided next time he would stand back and sell it to the insurance company. The damage from the energy in even a car battery is more then you want to deal with. Batteries also can explode.




As a young Lamp and battery maintence man, I managed to cause a flash over of hydygen on a row of automobile type batteries that were charging when the connectors came loose and I jiggled them and caused an arc.


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