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ekstra   ara
 Post subject: DC Arc Flash
PostPosted: Fri Oct 31, 2014 5:13 am 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 825
Location: Rutland, VT

I have been thinking about the ramifications of the DC Arc Flash Table 130.7(C)(15)(B) for a 125V, 60 cell, battery bank that is typical for generating stations and large substations. Yes, I know that installations under the control of utilities are not covered but this seems to be the only standard/consensus document that has DC arc flash in it.

Typically with the arrangement for 60 cells the positive connection is on one end and the negative connection on the other end or on a level below depending on how many tiers. Many battery inspections consist of a monthly bank voltage reading with a multimeter.

Now for a 125Vdc, 60 cell, 670 Ah battery the manufacturer's spec sheet has a short circuit current of 8,840 A. Using the table above, this results in a Arc Flash PPE Category of 3 and Table 130.7(C)(15)(A)(a) indicates that Arc Flash PPE is needed for voltage testing on series connected battery cells.

Considering the distance between the positive terminal and the end negative terminal, standard voltage leads supplied with a multimeter may not reach so many people have auxiliary leas made up to span the distance. Given that the risk of shorting out the entire battery bank with a multimeter with extremely small wire seems unlikely, isn't the PPE class of 3 a little extreme?


Barry Donovan, P.E.

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