It is currently Mon Dec 11, 2017 10:00 am



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Flash protection boundary
PostPosted: Tue Apr 24, 2012 5:22 am 
Offline

Joined: Sun Nov 20, 2011 5:00 pm
Posts: 7
Are the flash boundaries provided in the task table mandatory or suggested. If you default to the table must you use the listed boundaries?


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Wed Apr 25, 2012 3:30 am 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1820
Location: North Carolina
You answered your own question. If you use the tables, you use the boundaries listed in the table. Granted this may be nonsensical when the tables say "H/RC 0" for opening/closing a fused disconnect but then list an arc flash boundary.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu Apr 26, 2012 10:49 am 
Offline

Joined: Sun Nov 20, 2011 5:00 pm
Posts: 7
Thanks for the response Paul. I just have a mental block on those distances for some reason.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Apr 27, 2012 8:56 am 
Offline

Joined: Thu Apr 02, 2009 5:59 am
Posts: 6
Interesting you should ask this. I am looking for some guidance here, specifically on labeling to meet the specifications of Article 130.5(C) Equipment Labeling (Clause 4.3.5.4 up here in Canada). There appears to be a near-contradiction in wording. I have copied from CSA Z462-12 below (nearly verbatim for NFPA 70E):

Electrical equipment such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centres (MCCs) that are in other than dwelling units and that are likely to require examination, adjustment, servicing, or maintenance while energized shall be field marked with a label containing all the following information:
(a) at least one of the following:
(i) available incident energy and the corresponding working distance;
(ii) minimum arc-rating of PPE;
(iii) required level of PPE; or
(iv) highest hazard/risk category for the equipment;
(b) nominal system voltage;
(c) arc flash boundary; and
(d) date of the hazard analysis. (this last one is in CSA Z462-12 only, not in NFPA 70E)

So here's the conundrum: The arc flash boundary is only determined if incident energy is calculated at each bus otherwise the boundary is unknown. So, if an incident energy analysis has not been used and the tables of 130.7(C)(15)(a) and (b) (table 4A and 4B in CSA) are being used in place of calculated numbers, then it seems you should use the parameters as defined in the Table (ripped right out of table 130.7(C)(15)(a)):
- Panelboards rated 240V or below: HRC 1, AFB 19"
- Panelboards greater than 240V and up to 600V: HRC 2, AFB 30"
- 600V Class MCCs (65kA, 2cyc FCT): HRC 2, AFB 53"
- 600V Class MCCs (42kA, 20cyc FCT): HRC 4, AFB 165"
- 600V switchgear: HRC 4, 233"
etc. etc.

This is never an issue when I do my studies, since AFB is calculated with incident energy. Why I am concerned is that a client has asked me to print labels from a study another consultant did and he has requested I put an AFB of 15" (385mm) and an HRC 2 on labels for his 480V equipment. To me, this just doesn't make sense, since a working distance of 18" would be LESS than 1.2 cal/cm2 by that AFB given, which in the old world of corresponding HRC to incident energy (which I know we have moved away from) would be HRC 1. I did not do the study and I am just printing off the labels, but I really don't want to be the one providing these stickers with information that makes no sense.

Anyone have any guidance on this? I have told him that it may be best to use incident energy and working distance in place of HRC (as is now the common practice); at least that way I will have an opportunity to see if the incident energy does jive with those small arc flash protection boundaries.

Tim


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Apr 27, 2012 12:24 pm 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1820
Location: North Carolina
You may be seeing the result of a simplified PPE scheme. Since the PPE requirements are minimally different, it is quite common to see them grouped into a 3 level scheme (0, 1/2, 3/4) and to assign the highest level (2 in this case), or even a 2 level scheme (0/1/2, 3/4), especially for folks using the charts.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Apr 27, 2012 2:29 pm 
Offline
Sparks Level

Joined: Thu Jul 07, 2011 6:03 am
Posts: 59
Location: Netherlands
What is the idea behind no longer corresponding incident energy with HRC anyway? Prevent over-protection?

A simplified PPE scheme is the most practical way in industrial installations and PPE on the market is aligned to the cal/cm2 ratings in table 130.7(C)16 of NFPA 70E anyway. Expressing the required PPE as a HRC number - even if you calculate the hazard - still seems the best option to me.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Apr 27, 2012 3:13 pm 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1820
Location: North Carolina
jvrielink wrote:
What is the idea behind no longer corresponding incident energy with HRC anyway? Prevent over-protection?


Read the notes. The tables reflect a risk assessment where the PPE was reduced based on a reduced likelihood of occurrence of an arc flash. IEEE 1584 does not take likelihood into account at all. Thus the maximum H/RC value in each section of the table corresponds to the calculated incident energy. The other values reflect risk assessments considering likelihood.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Apr 27, 2012 4:28 pm 
Offline
Sparks Level

Joined: Thu Jul 07, 2011 6:03 am
Posts: 59
Location: Netherlands
Sorry, should have been more clear. The table I referred to is "Protective Clothing and Personal Protective Equipment (PPE)", not the classification of HRC based on tasks. For example, for HRC 2 it specifies a minimum Arc Rating of 8 cal/cm2 alongside what PPE is required.

This means that a calculated hazard between 4 and 8 cal/cm2 can still be linked to HRC 2 PPE requirements.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Apr 27, 2012 4:45 pm 
Offline
Arc Level

Joined: Wed Jun 04, 2008 9:17 am
Posts: 409
Location: Spartanburg, South Carolina
Assigning an AFB of 15" and an HRC of 2 to all 480 V equipment is OK if an analysis has shown that all incident energies are less than 8 cal/cm┬▓ and all AFBs are less than 15". It's OK to require single conservative values to simplify operations. I would recommened that the category 2 be called a PPE category instead of an HRC if no formal hazard/risk analysis was done.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Apr 30, 2012 4:27 am 
Offline

Joined: Thu Apr 02, 2009 5:59 am
Posts: 6
jghrist wrote:
Assigning an AFB of 15" and an HRC of 2 to all 480 V equipment is OK if an analysis has shown that all incident energies are less than 8 cal/cm┬▓ and all AFBs are less than 15". It's OK to require single conservative values to simplify operations. I would recommened that the category 2 be called a PPE category instead of an HRC if no formal hazard/risk analysis was done.

Agreed jghrist, especially on semantics between PPE level and HRC. As I had mentioned in my original posting, I do not know at this point if an arc flash analysis was done since I was only asked to print the labels (which makes me wonder why the original consultant didn't provide that service... o_O ). Your explanation would make the most sense as that AFB is not a standard boundary, and must have been calculated (I know the client and he wouldn't pull these numbers out of thin air, that much I know).

I want to rant a bit here on HRCs and PPE as was discussed above by Joost and Paul: In NFPA 70E-2012 (and CSA Z462), Annex H has been expanded from previous versions, specifically with table H.3(b) (Table H.2 in CSA Z462). I think this table came about specifically because of "modern day" class 2 PPE -- coveralls and work pants/shirts in particular; not the balaclava -- which is often now rated 12.4 cal/cm2 where the older stuff from about 4/5 years ago was 8.7 cal/cm2. The recommendation states that the typical class 2 PPE should be considered between 1.2 and 12 cal/cm2. That's pretty neat considering how frequently a "low" HRC 3 (like 8.1 cal/cm2) location would recommend an owner to dress their employees in the bomb suit, which I think adds other dangers compared to just doing work with normal work attire.

Nonetheless, Annex H is only an informative Annex and doesn't have to be followed; and MOST IMPORTANTLY, you must know what the rating of the work attire is used onsite before making any statements regarding PPE levels. The elimination of HRC/IE relationships and the expansion of Annex H will cause an owner to open a more thoughtful dialogue with the consultant doing the study, which I think is great. Ultimately, it shouldn't be the responsibility of the person crunching and reporting the numbers dictating what a worker should be wearing onsite (which in my experience many clients do try to put this responsibility on me). This decision has to be left to supervisors and management at the site itself. These subtle changes will assist in that regard and I really like the direction that they are starting to go with this standard.

Tim


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Apr 30, 2012 2:30 pm 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1820
Location: North Carolina
That is the reason that it is better to move towards using incident energy on the label and doing a task analysis to look at whether PPE should be required or not for a given task. Then your 8.7 cal/cm^2 rated clothing will work with an 8.1 cal/cm^2 panel, and only if you actually run a significant risk of occurrence of an arc flash hazard. The tables are there as a simplified approach. The rest of your post referring to Annex H is a bit confusing to me. The essential target of IEEE 1584 for analysis (Annex D) among others is to look at the minimum distance between the bus bars at the back of the cabinet where the incident energy is highest and the worker's face and upper chest areas where the fatality rate is the highest.


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
cron
© 2017 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883