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 Post subject: NFPA-70E Tables vs Calcs
PostPosted: Wed Jan 28, 2009 10:31 am 
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Hi-

I am an engineer doing a study on a large facility. This place has a full time staff of union electricians. They are very well versed on NFPA-70E, and the installation of labels with categories and IE is a big change.

Im trying to compare using the tables and shortcuts in NFPA-70E with performing full IEEE-1584 calculations.

NFPA-70E appears to completely seperate the requirements for Incident Energy calculations from the Arch Flash Protection Boundary. It seems intuitive to either use the tables and 4' distance for <600V, or do the full blown calculations for both.

Is it possible (obviously not practical :rolleyes: ) to have a calculated Arc Flash Protection Boundary per 130(A) AND task dependent PPE based on 130.7(C)(9),(C)(10), per 130(B), provided all system requirements were met?

My previous understanding was that the tasks and tables go out the window, and a PPE category is based on any work within a particular enclosure once calculations are performed and IE and FPB are established.

I'm trying to step back and see the big picture.
Thanks


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PostPosted: Wed Jan 28, 2009 10:56 am 
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Ex twidget wrote:
Hi-

I am an engineer doing a study on a large facility. This place has a full time staff of union electricians. They are very well versed on NFPA-70E, and the installation of labels with categories and IE is a big change.

Im trying to compare using the tables and shortcuts in NFPA-70E with performing full IEEE-1584 calculations.

NFPA-70E appears to completely seperate the requirements for Incident Energy calculations from the Arch Flash Protection Boundary. It seems intuitive to either use the tables and 4' distance for <600V, or do the full blown calculations for both.

Is it possible (obviously not practical :rolleyes: ) to have a calculated Arc Flash Protection Boundary per 130(A) AND task dependent PPE based on 130.7(C)(9),(C)(10), per 130(B), provided all system requirements were met?

My previous understanding was that the tasks and tables go out the window, and a PPE category is based on any work within a particular enclosure once calculations are performed and IE and FPB are established.

I'm trying to step back and see the big picture.
Thanks


You are correct, the 2009 70E strongly advises against mixing usage of the tables and arc flash analysis results. For a "large facility" you probally wont be able to use the tables much anyways. And using the tables will have your guys wearing "overprotection" in many cases, I have done many of thes in Union plants and can tell you that you have a very difficult task ahead of you dealing with the unions and the new rules and PPE requirements that your plant will need to implement.

Forget about the tables, or just use them for <240V <125kVA areas where you dont do the analysis.
1. Do your analysis
2. Determine what PPE will be necessary
3. Figure out how to mitigate the >40cal/cm2 areas you will find in a large industrial plant
4. Decide if your PPE will be daily wear or will be donned/doffed when needed (There are many things to consider with this)
5. Decide if you will purchase or lease your PPE
6. Have your Electrical Safe Work Practices updated to replect changes
7. Have your EEWP policies in effect
8. Determine who will be deeming these employees "qualified"
9. Have a disiplinary action plan for thise not in compliance
10. Determine how you will handle contractors in your plant for 70E compliance
11. Train your people, including, qualified, non qualified, and task specific qualified persons (Yep in your case training should be the last thing you do)


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PostPosted: Thu Jan 29, 2009 9:41 am 
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Thanks for your comments Zog.

The crew at the building has a program in place. They are all trained and embrace Arc Flash Safety. It's a building rather than a production type facility, so PPE is used for maintenance and troubleshooting only.
(Or for removing covers off dozens of panels for some @#$% engineer :cool: )

My difficulties with the tables in NFPA-70E is that they are excruciatingly **task** specific, for **general** classes of equipment. The electricians know what to wear to cycle a breaker, cover on or cover off. They know what kind of PPE to put on to inspect it or to remove it and reinstall it. IEEE-1584 tell us that all we need to know about tasks is 18", 24" etc.

Now we come in with our stickers. The stickers are unique for each piece of equipment, but have absolutely no information on tasks. They look at the same panel and say, Is this sticker for the cover on or cover off? Why aren't any of these rated Category 2*?

We are still in the process of completing our study and reviewing the initial results with the foreman. Retraining will obviously be required.

Since the momentum for the NFPA-70E appears to be headed towards requiring detailed studies for increasing numbers of installations, the wording should be tailored for this approach. Perhaps a handbook would be helpfull, simailar to what they produce for the NEC.

This forum has been a valuable resource and I appreciate all who contribute.

Ex twidget


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PostPosted: Thu Jan 29, 2009 9:59 am 
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Ex twidget wrote:
Thanks for your comments Zog.

The crew at the building has a program in place. They are all trained and embrace Arc Flash Safety. It's a building rather than a production type facility, so PPE is used for maintenance and troubleshooting only.
(Or for removing covers off dozens of panels for some @#$% engineer :cool: )

My difficulties with the tables in NFPA-70E is that they are excruciatingly **task** specific, for **general** classes of equipment. The electricians know what to wear to cycle a breaker, cover on or cover off. They know what kind of PPE to put on to inspect it or to remove it and reinstall it. IEEE-1584 tell us that all we need to know about tasks is 18", 24" etc.

Now we come in with our stickers. The stickers are unique for each piece of equipment, but have absolutely no information on tasks. They look at the same panel and say, Is this sticker for the cover on or cover off? Why aren't any of these rated Category 2*?

We are still in the process of completing our study and reviewing the initial results with the foreman. Retraining will obviously be required.

Since the momentum for the NFPA-70E appears to be headed towards requiring detailed studies for increasing numbers of installations, the wording should be tailored for this approach. Perhaps a handbook would be helpfull, simailar to what they produce for the NEC.

This forum has been a valuable resource and I appreciate all who contribute.

Ex twidget



Having task specific labels is a rare thing, most places dont do it because it causes too much confusion. The answer to the "covers on or off" question should be "both", the label should reflect the worst case senario.

The 70E does have a handbook and it is a valuable reference, but the additional notes are non enforceable, just there for clarification.


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PostPosted: Thu Jan 29, 2009 3:58 pm 
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Zog wrote:
The answer to the "covers on or off" question should be "both", the label should reflect the worst case senario.


How do you get both from your calcs. Calcs can be done for open air, or the five wall arc in a box. But how do model the sixth wall that fails after diverting some of the energy? The tables show HRC reduction for covers off, but if your clearing times don't match those of the tables there does not seem be any method of reducing the HRC for covers on.


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PostPosted: Thu Jan 29, 2009 8:17 pm 
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stevenal wrote:
How do you get both from your calcs. Calcs can be done for open air, or the five wall arc in a box. But how do model the sixth wall that fails after diverting some of the energy? The tables show HRC reduction for covers off, but if your clearing times don't match those of the tables there does not seem be any method of reducing the HRC for covers on.


I was responding to a question about labeling based on the task based tables, you are asking about calulations, apples and oranges.

You cant model a "6th wall, that fails after diverting energy", no way to do it, you just do the arc in cubic box calc and pretend the other wall is not there, how would you account for missing hardware or vents? Dont think of the tables as reducing HRC for covers on, becasue they are not purly factored on equations or models.


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