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 Post subject: New to Arc Flash
PostPosted: Thu Apr 02, 2009 1:07 pm 
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Hello all,

I am completely new to arc flash analysis and fairly new at electrical engineering in general. I was hoping to get a few questions answered, or at least help getting pointed in the right direction. For your information, I am conducting an Arc Flash analysis using ETAP. Here are my questions, I would appreciate any input that you guys have. Thanks a lot!

1. Is "Working Distance" a value that I define? Are there typical values for this? A table maybe?

2. Let's say that I generated an arc flash label using ETAP for a 4160V switchgear. Here is the information listed on the label:

Arc Flash Hazard Boundary
Incident Energy
Working Distance
Shock Hazard Exposure
Insulating Gloves Class
Shock Hazard
Limited Approach Boundary
Restricted Approach Boundary
Prohibited Approach Boundary
Hazard Category

Now, next to "Shock Hazard" is says "when covers removed". Next to "Arc Flash Hazard Boundary" it says "31.5 ft". Does this mean that when the door to the switchgear is open, that to be absolutely safe you have to be at least 31.5 feet away? What if the door is closed? Can you be as close as you want? Are all arc flash studies for open equipment?

3. Are there any typical guidelines for placing labels on equipment? For instance, any requirements for heights and number of labels? Any information on the actual labeling of equipment would be appreciated.

Thanks again for your responses!


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PostPosted: Thu Apr 02, 2009 1:35 pm 
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Welcome to the forum, apalmer15. The first thing I would suggest is that you browse this forum well initially. The reason for the short answer is that all of your questions have been answered here, or at least pretty thoroughly debated. Once you get totally confused, I expect you will be back with more and different questions.

And again....Welcome to our state of confusion!


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PostPosted: Thu Apr 02, 2009 6:45 pm 
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I would also suggest that you visit arcadvisor.com and read their literature.

There are standards for the working distance depending on voltage and equipment class, the ones at arcadvisor are standard. They are also listed in Art 130, check Annex D.

The 31 foot is the AFB, arc flash boundary, its the point past which you must have proper thermal PPE. It would generally only apply when the equiopment doors or covers are off or open, live exposed work. There are some cases like racking switchgear in which it applies with doors closed.

You got a lot of reading to do.


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PostPosted: Fri Apr 03, 2009 1:21 am 
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Totally agree with responses but a visit to brainfiller.com is an absolute must. There is a huge amount of literature and free downloads there that I have found extremely helpful.


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PostPosted: Fri Apr 03, 2009 5:00 am 
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Location: Aurora, Ontario, Canada
Short note about labels:
CSA Z462, 4.3.3.4:
Equipment shall be field marked with a label specifying the:
(a) available IE or required level of PPE; and
(b) date of evaluation.

According to Z462 4.3.3.1. arc flash assessment “shall be reviewed periodically, not to exceed five yearsâ€, so the date is important.
I’ve seen many labels without the date, this is a common mistake.


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PostPosted: Fri Apr 03, 2009 9:32 am 
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Eugene wrote:
Short note about labels:
CSA Z462, 4.3.3.4:
Equipment shall be field marked with a label specifying the:
(a) available IE or required level of PPE; and
(b) date of evaluation.


I'm not trying to argue with you, I think it is a great idea, but just to clarify date of evaluations is not present in the NFPA 70E.


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PostPosted: Fri Apr 03, 2009 6:36 pm 
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ditto, not in Art 130. I'm not sure what I think about putting the date on the label. I would think that in most cases there are NOT substantial changes to fault current over 5 years. My site has not changed fault current in 20 years. The 5 year periodic review will be a 2 hour lunch catered meeting with the engineering and Esha peers to review the one line and fill out a form that says there are no changes.


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PostPosted: Sat Apr 04, 2009 4:27 am 
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I would think it should also include a check with supplier to see if the available source fault duty has changed.


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PostPosted: Sat Apr 04, 2009 5:27 am 
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haze10 wrote:
ditto, not in Art 130. I'm not sure what I think about putting the date on the label. I would think that in most cases there are NOT substantial changes to fault current over 5 years. My site has not changed fault current in 20 years. The 5 year periodic review will be a 2 hour lunch catered meeting with the engineering and Esha peers to review the one line and fill out a form that says there are no changes.


As long as the state of the art regarding how to calculate the IE doesn't change. Or, if using Table 130.3(C)(9), it doesn't change in the next revision of NFPA 70E (it did between 2004 and 2009). Or the notes concerning usability of said table. Or the characteristics of an upstream protection device (inside your facility).


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PostPosted: Sat Apr 04, 2009 6:27 am 
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Vincent:
Don't know how you can say you have done a complete review without a check of the source.

Haze:
Just because it hasn't changed in 20 years doesn't mean it will not in year 21. We are planning to install a new sub now at a location where the customers are about 3 to 4 miles from the existing source and the fault duty in that area will probably double or triple. The fault duty in that area probably has not changed in many years. Could easily affect service entrance equipment ratings if it is 20+ years old.

What if your supplier has replaced your service transformer with a larger one?

I agree that it may not have changed, but how do you know unless you ask the question?


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PostPosted: Sat Apr 04, 2009 5:16 pm 
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Wow, we are a very literal group.

Obviously, I will check with the utility supplier. But since we are on an intrastate feeder they would have to have changed one of their largest substation in the State. Also, when I did my original calcs, I did it with the fault MVA they supplied at that time, at 25% more, and 25% less and took the highest resulting IE. So they would need to make one big change. Plus my 480 is two transformer down stream, so there is a lot of impedance before getting to the 480V labels.

Naturally, if I make a change on site, changing a transformer or cable feeder, I would need to check the calcs. This goes without saying. But if I know there has been NO feeder or xfrm upstream changes, the only thing I need to check is the utility MVA. As long as it comes back at the original +/- 25% - then its back to desert after the main course at lunch.

If the nfpa changes the task matrix, then you would have to redo the labels for those categories that changed and if those categories were on the label. But the only analysis would be to check that the table was still applied within its limits.

This brought up the previous question I raised on how one is supposed to follow the table and still label IE or HRC. You can't put every task in the table on a label, so you are only going to list those most common to you, ie check voltage, insert bucket, etc. nfpa has not left us much explanation as to how to list PPE and IE when using the table.


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PostPosted: Mon Apr 06, 2009 6:38 am 
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I agree Haze, your comments were a little misread.

Good thought though on the date not being there. If you do go through the proper procedure for updating or verifying that the study is still valid. and nothing has changed than your labels are fine. No need to reprint just because of the date.

I will say that Vince is probably right I think after this next round of IEEE testing that is taking place we will have new or altered calculation methods that would change the study.


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PostPosted: Mon Apr 06, 2009 5:28 pm 
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I sure hope note. The NFPA has to learn that there is a financial hardship borne by industry in meeting these codes. The goal of the NFPA is financial, I am convinced of that. If they don't change the codes they don't sell books. Quite frankly I think we should have stopped with the 2004 code edition and given it 10 years to see the results. We probably didn't need the 2009 edition at all. Going to a full analysis only method, which seems to be where we are heading, is going to hurt all US industries.


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PostPosted: Wed May 06, 2009 7:53 pm 
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My opinion is that all engineering work should be dated, if for no other reason than to protect the engineer by referencing codes in place at time of completion. 5 year interval on revisiting the study might correspond with NETA recommendations for swgr maintenance and when protective settings might be changed. Having dates on the labels we've installed has also been a good practical matter in checking how well they are weathering :) .


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