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 Post subject: PPE Category Tables and NO Category 0
PostPosted: Fri May 01, 2015 11:36 am 
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Joined: Sat May 17, 2008 5:00 pm
Posts: 77
Is anyone else having a difficult time with the elimination of category 0? There were a few tasks that we could get by without arc rated PPE etc. and now it seems we need it except for just a few exceptions defined by the new Yes/No Arc Flash PPE required table. It is affecting how we do things.


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 Post subject: Re: PPE Category Tables and NO Category 0
PostPosted: Fri May 01, 2015 2:56 pm 
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Joined: Tue Oct 26, 2010 9:08 am
Posts: 1806
Location: North Carolina
What's the problem? Everything starts at 1.3 cal/cm^2 and above. Below that point, "H/RC 0" did not disappear...it's just that there is no longer any requirement at all.

If you were using the TABLE method, I agree things got much worse. Prior to 2015 edition, there were numerous instances where the risk of an injury was less but the hazard was the same. Thus we had several difference H/RC values for the exact same equipment even when the hazard didn't change. The 2015 edition now recognizes that when the likelihood ("risk") is so low, PPE should not be required. Otherwise the full PPE level required for that type of equipment is required as per the equipment table. The concept of "derating" no longer exists, which reflects reality.

In almost all cases we went from H/RC 0 or sometimes H/RC 2 to no PPE required at all. And now you are saying that PPE is required most times compared to previously. That doesn't sound right.


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 Post subject: Re: PPE Category Tables and NO Category 0
PostPosted: Fri May 01, 2015 5:21 pm 
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Posts: 77
Here is one that comes up a lot. Maybe I'm missing something.

2012 Edition
Work on control circuits with energized electrical conductors and circuit parts 120 V or below, exposed - Category 0

2015 Edition
Panelboards or other equipment rated 240 V and below - Category 1

What I am thinking of are 120V control type circuits and single phase circuits when we don't perform the calculations. It seems now we need to wear PPE for this type of work unless we perform calculations and show it is less than 1.2 cal. i.e. the tables now require PPE whereas before they did not for this case.

Thanks!


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 Post subject: Re: PPE Category Tables and NO Category 0
PostPosted: Sat May 02, 2015 12:30 pm 
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Joined: Tue Oct 26, 2010 9:08 am
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Location: North Carolina
K. Engholm wrote:
Here is one that comes up a lot. Maybe I'm missing something.

2012 Edition
Work on control circuits with energized electrical conductors and circuit parts 120 V or below, exposed - Category 0

2015 Edition
Panelboards or other equipment rated 240 V and below - Category 1

What I am thinking of are 120V control type circuits and single phase circuits when we don't perform the calculations. It seems now we need to wear PPE for this type of work unless we perform calculations and show it is less than 1.2 cal. i.e. the tables now require PPE whereas before they did not for this case.

Thanks!


There is no calculation method that is valid for below 208 V other than the Lee theoretical method, and even that's questionable. IEEE 1584 claims accuracy down to 208 V but it relies on only a single sample where the arc was actually stable enough to get a result. All other cases failed to form a stable arc. So again, questionable. The guidance in IEEE 1584 is that you need not do modelling at 208 V or below with a single transformer rated 125 kVA or less. More recent test work has suggested pushing this down to the 45-60 kVA range but so far no update to IEEE 1584 and it may take a while. NESC tables give a result of 4 cal/cm^2 or less based on test data by EPRI and several utilities for a variety of cases where I think the highest actual test result I spotted is 3 cal/cm^2. And there was a fatality in 2009 in Georgia when a couple electricians decided to disassemble a construction temporary panel before the lineman got there to disconnect it, as reported in OSHA investigation data. So a fatality or serious injury at 240 V and below is POSSIBLE, however rare.

My approach right now is to use the IEEE 1584 "exception" where it applies, <1.2 cal/cm^2 for 125 V or lower DC batteries based on test data from Duke (done at Kinetrics @ 130 V), and use 4 cal/cm^2 based on either 70E or NESC tables for everything else. Eventually I may have to decrease the exception down to around 4-5 kA irrespective of the kVA rating of the transformers when IEEE 1584 gets revised. NESC table starts at 4 cal/cm^2 because this has become somewhat of a utility standard and more recently, OSHA's revisions to 1910.269 set it up as a floor due to concerns about secondary issues such as being hit with molten metal.

This was already happening in the 2012 edition of 70E when the "exception" (restated from IEEE 1584) was removed so for the low voltage cases we rolled it up to use IEEE 1584 which still provided the same exception. We also extended the "coverage" to values above the "exception" by using the NESC tables. My predecessor was so hung up on IEEE 1584 that he even went in and changed a lot of lighting circuits from 240/120 single phase to 208/120 V 3 phase just to match the exception.


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