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 Post subject: PPE and IE below 1.2
PostPosted: Sun Mar 09, 2008 7:21 pm 
Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 483
Location: New England
I need some clarification.

When using the NFPA Matrix you have the option in some categories and some tasks to drop the PPE by one level.

[1] Maximum of 25 kA short circuit current available, 0.03 second (2 cycle) fault clearing time.
[3] For <10 kA short circuit current available, the hazard/risk category required may be reduced by one number.

This would of course assume that you meet the above requirements as cited in the notes. This would also allow you in some circumstances to drop to Level 0.

Now, if we were calculating PPE with the analysis method using IEEE formulas, are there any situations in which you can employ Level 0? The NFPA table lists PPE level 1 with an upperlimit of 4 cal/cm2, but there is no listing for Level 0.

So if you calculate an IE of say 0.05 cal/cm2 and the Ibf was less than 10K - are you still in Level 1?

Along this same theme, the Arc Flash Boundary is the point at which IE is reduced to 1.2 cal/cm2. But at that point you have unqualified individuals who are dressed in polyester shirts. Does this make sense?

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PostPosted: Tue Mar 11, 2008 9:18 am 

Joined: Sun Mar 02, 2008 2:02 pm
Posts: 20
Location: Spokane Wa
The way that I look at it is that you can either use the NFPA matrix OR the IEEE calcs.

So basically if you do the calculation with IEEE then you have to use the IE that it is calculating to determine the PPE. However if you simply use the matrix then you can do as you note. That said I don't think that this is necessarily the correct or safest way to do something.

Most of the remote sites that I work on have a available fault level of 10kA or less, but the protection takes a long time to clear a fault which increases the IE dramatically.

So no, it doesn't really make sense, but remember that the entire discussion on Arc Flash is new and growing, so this is something that I am sure will be addressed in the future.

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PostPosted: Sun Mar 23, 2008 7:20 pm 
Sparks Level

Joined: Thu Oct 18, 2007 7:10 pm
Posts: 250
Location: NW USA
I agree with Bluenoser: if IEEE calculations are used to determine arc flash energy level, that should be the minimum PPE used, regardless of other provisions.

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