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Have you/co-worker/client/consultant ever caught a mistake on an arc flash calculation study?
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 Post subject: Arc Flash Study Mistakes
PostPosted: Sun May 27, 2012 2:18 pm 
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Arc flash calculation studies can be quite complex. Data collection, system modeling, calculations, there are plenty of opportunities for errors.

Have you, your co-worker, client or consultant ever caught a mistake on an arc flash calculation study?

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Not that I will admit

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PostPosted: Mon May 28, 2012 6:11 am 
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We had a consultant insist the infinite bus utility fault current was the worst case. I think they just did not want to take the time to track down the utility data.


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PostPosted: Mon May 28, 2012 8:33 pm 
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Jim as you know this is one of my biggest concerns. In the detailed Electrical Safety Audits I performed I review engineering incident energy analysis study reports and more specifically the detailed labels installed on the electrical distribution equipment. Problems with the labels and information not matching the report, wrong working distances, HRC #s on the label (historically included and a tough up hill battle with the die hards that can't seem to realize there is not techical correlation between incident energy and an HRC #), location wrong, equipment identification wrong, wrong label on equipment, not all labels applied, label doesn't meet ANSI Z535.

I actually came across two different clients who hired a large equipment manufacturer to complete the engineering incident energy anlaysi studies. I told both clients to remove all of the "Danger" labels immediately, one label was 0.7 cal/cm2. All labels applied use the "Danger" signal pane word, and used words like "death", HRC #s, marketing text at the bottom, etc.

I actually contacted the large equipment manufacturer and I was told the marketing and legal department controlled the label format not the responsible P.Eng.

The last two paragraphs are an unfortunately example and not the only one of the "arc flash economy" that has developed and the large equipment manufacturer's and large EPCM firms are attempting to shed all lialibility for doing engineeing for their client.

I am also finding that on large capital projects the EPCM doesn't release a P.Eng./P.E. Stamped report before the electrical power system is energized, I have a two clients right now where the power systems have been energized over 12 months and no study. I can't believe that the large equipment manufacturer and large EPCM are getting away with this.

We all have to keep pushing to "Make it Right!!"

Regards;
Terry


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PostPosted: Tue May 29, 2012 5:37 am 
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I reviewed an AF study done by probably the same large equipment manufacturer as mentioned in the post above where they ignored several points on the system and only provided labels on the MCCs never looking dowstream of the system. The distances assumed were completely off, assuming 5 feet where in reality the distance was 300 feet.

Marek


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PostPosted: Fri Jun 01, 2012 9:23 am 
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I was called in to review a study conducted by probably the same large well know electrical equipment mfg as mentioned above posting. Found almost 80% of the equipment mislabeled with the wrong cal/cm^ and ppe. All labels used "Danger" even if it was 1.2 cal/cm^. They hired the company because the quoted price was lower than a professional consulting firm or engineer. The well know equipment mfg even offered to not provide labels as an option to save on the cost.


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PostPosted: Thu Jun 07, 2012 6:23 am 
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Terry Becker wrote:
... Problems with the labels ...HRC #s on the label (historically included and a tough up hill battle with the die hards that can't seem to realize there is not techical correlation between incident energy and an HRC #)...


Terry,
My perspective regarding HRC (Hazard/Risk Category) numbers on IEEE 1584-based labels is that it is acceptable even if risk hasn't been factored in. The industry jumped to the "task tables" when arc flash became an issue in NFPA 70E and so they are familiar with the category concept. If my analysis shows 7 cal/cm2 at a specific location, then my arc flash label reads "Category 2 PPE Required". If a worker dresses to "Hazard/Risk Category 2" then they are protected for this location. What is your problem with that approach?

The label doesn't include the word "risk" (or the concept) but I believe the label does correlate with the protective clothing and PPE described in NEC Table 130.7(C)(16). Am I correct that if the worker dresses according to this table that they will be appropriately protected for the incident energy? I recognize that Table 130.7(C)(16) (which describes categories 0-4) is intended to directly correlate with Table 130.7(C)(15) (task tables), but why can't it also correspond to incident energy? In the example above, 7 cal/cm2 is rounded up to 8 cal/cm2 and HRC 2 is used.

Even though HRC 0-4 includes the risk concept, why can't the same categories be used for incident energy? In my facility, the electricians have three basic PPE configurations; category 0, 2 or 4. The choice of what category to use is based on IEEE 1584 calculations, and the specific PPE requirements for that category are based on Table 130.7(C)(16). My label doesn't include the word "risk" or "HRC", just the word "category".

I may be misinterpreting your statement above, but it sounds like you have a problem with my approach. What is your perspective on this approach? I may be a die hard you are referring to above, but I'd like to be a thinking die hard who understands both perspectives.

Regards,
Matt B


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PostPosted: Thu Jun 07, 2012 8:06 am 
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MattB wrote:
In my facility, the electricians have three basic PPE configurations; category 0, 2 or 4. The choice of what category to use is based on IEEE 1584 calculations, and the specific PPE requirements for that category are based on Table 130.7(C)(16). My label doesn't include the word "risk" or "HRC", just the word "category".


So if your calculations show a result of 8.2cal/cm² you make your workers dress in a HRC 4 outfit?

I just made recommendations (adjusting breakers settings only) that would lower the incident energy from 22cal/cm² down to 8.2cal/cm². The customer declined to implement these changes because it did not result in a lower HRC. However they did make the changes (new equipment) that lowered one location from 11cal/cm² to 7.9cal/cm².


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PostPosted: Thu Jun 07, 2012 8:43 am 
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JBD wrote:
So if your calculations show a result of 8.2cal/cm² you make your workers dress in a HRC 4 outfit?


Unfortunately that is correct. It's not economical to buy a suit at every level for a few dozen workers. Would you recommend something different? Does anybody out there run a calculation with a working distance of 20 inches in this type of scenario?


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PostPosted: Thu Jun 07, 2012 4:50 pm 
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Matt:

HRCs shall NOT be on detailed arc flash and shock warning labels when engineering indident energy analysis studies are completed.

Arc rated clothing is labelled with an ATPV or EBT, NOT an HRC. ASTM F1959 doesn't establish an HRC for FR clothing is determines the arc rating in an ATPV or EBT.

Using the word "Category" implies HRC, the Qualified Electrical Worker will default to this thinking especially if the training you sent them on had an instructor that didn't know what they were talking about.

IEEE P1584 calculates incident energy NOT an HRC.

Please advise me on how you justify that an HRC # should be on a detailed label when incident energy is calculated?

Please refer to Annex H where a new Table has been added indicated arc rated PPE when engineering incident energy analysis completed dividing arc rated clothing into three "Levels." Ultimately a company's Electrical Safety Program should identify arc rated clothing by arc rating levels, where Level 0 is 100% natural fibre clothing.

Level 0 = 100% natural fibr
Level 1 = Min 8 cal/cm2 ATPV or EBT
Level 2 = Min 40 cal/cm2, but can be 55, 65 cal/cm2 (I now recommend companies Standardize on 65 cal/cm2)

Please also note that there is NO CUT OFF for energized electrical worker based on incident energy in 70E/Z462.

Regards;
Terry


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PostPosted: Thu Jun 07, 2012 5:17 pm 
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MattB wrote:
Unfortunately that is correct. It's not economical to buy a suit at every level for a few dozen workers. Would you recommend something different?

Sure, we simply require clothing with an ATPV greater than 8.2 cal/cm².

Have you looked at section H.3 in Appendix H in NFPA 70E? We follow Table H3(b).


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PostPosted: Fri Jun 08, 2012 7:54 am 
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Gentlemen,

Thanks for taking time to share your interpretations. This type of discussion is why this forum is valuable.

In my (limited) experience, employers who cared about arc flash initially jumped to the “task tables” because they appear to be simple and easy to use at first glance. PPE was bought for these purposes with Category 2 rated for 8 cal/cm² and Category 4 rated for 40 cal/cm². I’ve worked for two employers, and both basically settled on a simplified three category system (Cat 0, Cat 2, Cat 4). Then in the 2012 version of NFPA 70E, Informative Annex H was overhauled and this issue of HRC (hazard risk category) verses IE (incident energy) clothing systems was “clarified”. I admit I just recently understood the significant difference.

My problem is that the workforce has already become familiar with HRC 2 (8 cal/cm²) and HRC 4 (40 cal/cm²). Then the 2012 code adds the concept (in annex table H.3(b)) of level 1 (12 cal/cm²) and level 2 (minimum 40 cal/cm²).

I’m not convinced that the code (NFPA 70E) forbids using the Category concept for an incident energy analysis. For example, I’m not convinced that it’s unsafe to label an MCC with 7.2 cal/cm² incident energy as “Category 2”. I recognize that the new (2012) annex adds language that includes guidance on selecting PPE for use when incident exposure is determined by a hazard evaluation. I get it. But the annex also starts with the sentence; “This informative annex is not a part of the requirements … but is included for informational purposes only.”

Terry Becker wrote:
Terry Becker wrote:
Terry Becker wrote:
HRCs shall NOT be on detailed arc flash and shock warning labels when engineering indident energy analysis studies are completed.

Regards;
Terry

Terry, I’m afraid I still don’t understand why you use the language “shall NOT” with this issue. I don’t see where the code forbids it. Down south(ish) where I live, “shall NOT” language is generally limited to Sunday school and the Ten Commandments.

Terry Becker wrote:
Terry Becker wrote:
Terry Becker wrote:
Please advise me on how you justify that an HRC # should be on a detailed label when incident energy is calculated?
Terry

I justify it because of history. People are generally educated about Category 2 and 4, so why fight it. I understand it’s not the recommended practice in the annex, but I don’t see why it’s wrong. To start using “Level 1” or “Level 2” on a label could be confused with the previous category system. If the label reads “Category 2 PPE required” I feel confident that my coworkers will know what that means and I feel better about outside contractors coming into my facility and interpreting the label. My electrical superintendent wanted all the information possible on the label, so that’s the direction we went. The following (and more) are included on my label; incident energy, category, PPE description, AF boundary and shock boundaries.

I'mnot saying that a category should be on a label, I'm saying that it may be on a label.

Jim Phillips, our forum host,
Do you want to comment on this issue? In an article from 2009 (http://brainfiller.com/admin/ArticleFile/EC%20Read%20the%20Label%20Jim%20Phillips%20SEP2009.pdf) you include both the category and the incident energy on your suggested label. Have you updated your position with the 2012 update, or do you stand by your 2009 article which some (not me) might say is an incorrect die-hard position.

Terry Becker wrote:
Terry Becker wrote:
Terry Becker wrote:
Please also note that there is NO CUT OFF for energized electrical worker based on incident energy in 70E/Z462.

I’m sure you’ve heard the argument, but for the sake of the post I have to include it. NPFA 70E-2012 section 130.7 Informational Note No. 3 states; “When incident energy exceeds 40 cal/cm² at the working distance, greater emphasis may be necessary with respect to de-energizing before working within the limited approach boundary…” My employer interprets this as an implicit cut off point. Due to the reasons discussed in the following article, we all likely agree that there is some cut off point (http://brainfiller.com/admin/ArticleFile/EC%2040%20Cal%20Arc%20Blast%20MAY2011.pdf).

I’m not going to get into a suit rated for 106 cal/cm² and expect it to protect me from all the molten metal and other hazards of a 106 cal/cm² explosion. I won’t ask a coworker to do it either. Surely you must agree that there is a cut off point somewhere (even if you don’t agree it is 40)?

JBD wrote:
Sure, we simply require clothing with an ATPV greater than 8.2 cal/cm². Have you looked at section H.3 in Appendix H in NFPA 70E? We follow Table H3(b).

JBD,
Whether you use the category system (1.2, 8, 40) or the Annex H.3 system (1.2, 12, ~40), you are going to have a point where you jump to the next step. For me 8.2 rounds up to 40. For you 12.2 rounds up to 40. My facility already has several dozen personnel with 8 cal/cm² suits so that’s where we’re sticking for now.


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PostPosted: Tue Jun 12, 2012 1:34 pm 
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MattB wrote:

Jim Phillips, our forum host,
Do you want to comment on this issue? In an article from 2009 ([url='http://brainfiller.com/admin/ArticleFile/EC%20Read%20the%20Label%20Jim%20Phillips%20SEP2009.pdf']http://brainfiller.com/admin/ArticleFile/EC Read the Label Jim Phillips SEP2009.pdf[/url]) you include both the category and the incident energy on your suggested label. Have you updated your position with the 2012 update, or do you stand by your 2009 article which some (not me) might say is an incorrect die-hard position.


Yes, I'm one of the die hards Terry spoke of. He is a good friend and well repected in the industry. We agree on most things but with this one, we still poke at each other from time to time. The point I agree with is HRC does mean something different. It factors in risk which the calculations do not.

I do believe you can lump calculations into "buckets" You can call it bucket 1, bucket 2, etc. That is why the industry migrated towards calling it a level and this method is still widley used. I had a survey question of the week about this a while back. The new problem we now have with the "bucket" model (just made that term up :) ) is that as new arc ratings emerge, they don't always fit easily into one of the buckets.

NFPA 70E did change the label requirements as most are probably aware. It was going to remain along the lines of "one or the other" like the 2009 edition however it changed at the last minute to allowing multiple selections. i.e. arc ratings, levels etc. I heard from one of my NFPA 70E committee friends that they changed it at the 11th hour" I was pretty vocal about this issue and it was nice to see the change.

Logically, placing incident energy into "buckets" works. However, I have migrated towards using only the arc rating of the PPE (with all of the other required info like AFB etc.). The reason is becuase of arc ratings like 12 cal/cm2. Not exactly going to fit the traditional 4, 8, 25, 40 cal/cm2 cut offs.

I also prefer listing only the arc rating becuase then when a study is reviewed, if the incident energy changes (and it likely will a little bit) you don't need to re-label as long as the arc rating is still OK. Some might argue that the AFB would change if the Ei changes but I have advocated for a very long time to use larger, more standardized Arc Flash Boundaries. So again, unless a new calculation requires changing a standard AFB, you don't need new labels. [url='http://www.brainfiller.com/News/NewsDetails.aspx?PRId=39&Type=U'][Standardized Arc Flash Boundary Article][/url]
MattB wrote:
[SIZE=3]Jim Phillips, our forum host,[/size]

[SIZE=3]I’m sure you’ve heard the argument, but for the sake of the post I have to include it. NPFA 70E-2012 section 130.7 Informational Note No. 3 states; “When incident energy exceeds 40 cal/cm² at the working distance, greater emphasis may be necessary with respect to de-energizing before working within the limited approach boundary…” My employer interprets this as an implicit cut off point. Due to the reasons discussed in the following article, we all likely agree that there is some cut off point ([url='http://brainfiller.com/admin/ArticleFile/EC%2040%20Cal%20Arc%20Blast%20MAY2011.pdf']http://brainfiller.com/admin/ArticleFile/EC 40 Cal Arc Blast MAY2011.pdf[/url]). [/size]

[SIZE=3]I’m not going to get into a suit rated for 106 cal/cm² and expect it to protect me from all the molten metal and other hazards of a 106 cal/cm² explosion. I won’t ask a coworker to do it either. Surely you must agree that there is a cut off point somewhere (even if you don’t agree it is 40)? [/size]

This is one of those questions that is a matter of interpretation and legal/liability . Since there is a long standing informational note about the 40 cal/cm2 cut off in NFPA 70E and not much else to go on, many take this as a hard fast number. In fact, the blast is more about energy per time. There is a very large difference between 40 cal/cm2 over 100 cycles and 40 cal/cm2 over 6 cycles. Right now it still remains a bit of a gray area. I addressed this (in a gray area sort of way o_O ) in the article you reference which is also listed here. [url='http://www.brainfiller.com/News/NewsDetails.aspx?PRId=61&Type=U'][40 cal/cm2 article][/url][url='http://www.brainfiller.com/News/NewsDetails.aspx?PRId=61&Type=U'].[/url]Great Discussion!

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PostPosted: Mon Jun 18, 2012 6:43 am 
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brainfiller wrote:
The new problem we now have with the "bucket" model (just made that term up :) ) is that as new arc ratings emerge, they don't always fit easily into one of the buckets.

Easy: arc rating of 8 cal/cm^2 would be Bucket 8 (or B8), arc rating of 12 cal/cm^2 would be Bucket 12 (or B12). That way, you can fit any new value between existing ones. You can even split it to decimals. Ah, the beauty of real numbers...
Personally, I'm waiting for B52, so I'll have a 30% safety margin over the 40 cal/cm^2 "limit".


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PostPosted: Mon Jun 25, 2012 8:42 am 

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A mistake I have seen is defining the equipment in the model incorrectly. Defining LV switchgear as a panel changes the gap and working distance and unless you are aware of this, using a "default panel" designation can be quite a problem. The results will be different.


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PostPosted: Mon Jun 25, 2012 8:43 am 

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A mistake I have seen is defining the equipment in the model incorrectly. Defining LV switchgear as a panel changes the gap and working distance and unless you are aware of this, using a "default panel" designation can be quite a problem. The results will be different.


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PostPosted: Mon Jun 25, 2012 12:29 pm 

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One of my pet peeves is when consultants use assumed data like every transformer having a 5.75% impedance. Really?


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PostPosted: Mon Jun 25, 2012 12:30 pm 

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One of my pet peeves is when consultants use assumed data like every transformer having a 5.75% impedance. Really?


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PostPosted: Fri Jun 29, 2012 9:10 am 
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In the process of doing a study for a large new england college I found a 750kva, 13.8kV/0.48kV padmount xfmr with a 1.9% Z. ANSI Std typical is 5.75%. Significant difference in fault current number between 1.9% and 5.75%

I've seen several studies where the company doing the study used ANSI impedance numbers. I guess they were too lazy to collect the field data.


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PostPosted: Thu Jul 12, 2012 8:22 am 
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Terry Becker wrote:
Matt:

HRCs shall NOT be on detailed arc flash and shock warning labels when engineering indident energy analysis studies are completed.


Using the word "Category" implies HRC, the Qualified Electrical Worker will default to this thinking especially if the training you sent them on had an instructor that didn't know what they were talking about.

IEEE P1584 calculates incident energy NOT an HRC.

Please advise me on how you justify that an HRC # should be on a detailed label when incident energy is calculated?


Hi Terry,

We spoke several times a few years ago when you started your interest in arc flash work. You may wish to aquire a copy of NFPA 70E 2012 which allows both incident energy calculated and HRC. [Specified in 130.3(C)(1)]. I am not aware of what concern you might have to declare this an error; we've been labelling operating plants since at least 2005 and were specifically requested by operating staff to put the HRC on the labels to simplify the understanding the PPE requirements.

I think it is good to remind ourselves that at the end of our work, an electrician is going to be seeking simple guidance without a lot of interpretations (or acronyms :) ).

Regards,

Gary B


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