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 Post subject: Category 0 vs Category 1
PostPosted: Fri Jul 02, 2010 7:29 am 
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Posts: 53
I have completed an arc flash study for a 240v 3 phase system. The results are primarily Category 0. Bolted fault currents of 4.4ka, arcing currents 2.6ka, with quick clearing times. My concern is the difference in the software result of Category 0 and how it compares to table 130.7 C9 in 70E. For example, the table for a 240 volt panelboard shows some tasks at Cat 0 but to remove a bolted cover a Cat 1.

Any suggestions on how to interpret these differences?

Thanks for your help.


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PostPosted: Fri Jul 02, 2010 9:03 am 
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Joined: Mon Jun 02, 2008 11:58 am
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Location: Charlotte, NC
mountaineer wrote:
I have completed an arc flash study for a 240v 3 phase system. The results are primarily Category 0. Bolted fault currents of 4.4ka, arcing currents 2.6ka, with quick clearing times. My concern is the difference in the software result of Category 0 and how it compares to table 130.7 C9 in 70E. For example, the table for a 240 volt panelboard shows some tasks at Cat 0 but to remove a bolted cover a Cat 1.

Any suggestions on how to interpret these differences?

Thanks for your help.


The tables make a bunch of assumptions and become void after you have done the analysis.


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PostPosted: Fri Jul 02, 2010 10:04 am 
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Location: Wisconsin
mountaineer wrote:
Any suggestions on how to interpret these differences?


Yes, ignore the tables once you have performed an analysis and have the actual incident energy levels.


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PostPosted: Tue Jul 06, 2010 5:08 am 
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Thank you for your replies. My brain can't seem to get past a Category 0 label for taking off a bolted cover while energized. Seems like a false sense of security.

I guess if the employees are properly trained they understand that Category 0 does not mean zero hazard.


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PostPosted: Tue Jul 06, 2010 10:06 am 
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Location: Wisconsin
mountaineer wrote:
...Category 0 does not mean zero hazard.

Very important point.

And of course, your work practices can be more restrictive than the bare minimum. For example, our service reps are to dress in Cat 2 when removing covers.


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PostPosted: Tue Jul 06, 2010 8:38 pm 
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JBD wrote:
Very important point.

And of course, your work practices can be more restrictive than the bare minimum. For example, our service reps are to dress in Cat 2 when removing covers.


We do the same, in order to avoid confusion, we require a minimum Cat 2 where Cat 1 is acceptable, and at any time live parts are exposed, whether by unbolting or opening a hinged enclosure.


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PostPosted: Wed Jul 07, 2010 5:14 am 
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In cases where the company's work practices require a higher hazard category than the study, how do you label the equipment? Do you print the label as a cat 0 based on the software calcs or do you label it a cat 2 based on work practices? I was checking around in etap to see if it is possible to force a higher category to print with the real calculated data. Haven't seen this function so far.


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PostPosted: Wed Jul 07, 2010 5:34 am 
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Location: Yankton SD/ Lead SD
We have a minimum Cat 2 level on our equipment. In SKM and ESA you can force the Cat level to whatever number you want. We print our labels with the Cat 2 being the lowest allowable PPE.


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PostPosted: Wed Jul 07, 2010 6:02 am 
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Thanks for the info. I'll keep looking at the software then. Must be in there somewhere.


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PostPosted: Wed Jul 07, 2010 10:59 am 
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Location: Wisconsin
mountaineer wrote:
Thanks for the info. I'll keep looking at the software then. Must be in there somewhere.


In SKM V6.5xxx it is one of the Options available on the Arc Flash results screen.


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PostPosted: Thu Jul 08, 2010 7:08 am 
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Found it! Thank you.


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