It is currently Thu Nov 23, 2017 4:52 pm



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Support Public Input 130 - Commercial Tables for Arc Flash
PostPosted: Fri May 08, 2015 10:35 am 
Offline
User avatar

Joined: Tue Oct 02, 2007 7:23 pm
Posts: 40
Location: Houston, Texas
With the encouragement of others in the industry, I have submitted Public Input 130 to the NFPA 70E. Take a look at the input and provide support in any way you can.

The basis of Public Input 130 is Flash Tables Unlimited which is currently available on-line; the input offers the idea to add this product as tables in the form of an additional Appendix. The tables are to be used in the commercial industry where things are highly standardized, where the tables are the best match for.

This will increase compliance within the electrical industry, especially the commercial industry where for the most part, electricians are still exposed on a daily basis. The tables are mostly based on IEEE 1584 equations, but also industry standards. One of the main reasons the commercial industry is not compliant is the ongoing cost and initial investment that is required. The tables can also be used in both the commercial and industrial industry to determine hazards in the early design stage, where major decisions are still being made.

In 2005, the IP owner of Flash Tables Unlimited, developed a shortcut method for arc flash which led to a $2 million dollar savings and led to an IEEE paper "How To Form A Bounding Arc Flash Study for Your Site" which was presented at many conferences in the US, Canada and overseas. The method described in the paper was the spark behind the madness, but is not the method behind the arc flash tables. The IP owner also served on the IEEE 1584 Committee from 2005-2008.

We hope you will support this Public Input. It is pro-business.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Mon May 11, 2015 8:37 am 
Offline
Sparks Level

Joined: Mon Jun 07, 2010 9:40 am
Posts: 119
"The method described in the paper was the spark behind the madness, but is not the method behind the arc flash tables."

Doesn't this imply that your "method behind the table" is unpublished, and therefore unknown?


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Mon May 11, 2015 9:48 am 
Offline
User avatar

Joined: Tue Oct 02, 2007 7:23 pm
Posts: 40
Location: Houston, Texas
The method behind the tables is personal IP, however, the results of the tables are published on-line. The tables are currently available as Flash Tables Unlimited.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Mon May 18, 2015 8:39 am 
Offline
Sparks Level

Joined: Mon Jun 07, 2010 9:40 am
Posts: 119
And there fore an unverifiable "black box".

which to be certain, seems to be how large parts of 70E come to be,
but in that particular case, I am certain that there is a lot more discussion and consensus involved.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Tue May 19, 2015 2:10 pm 
Offline

Joined: Mon Nov 10, 2014 11:01 am
Posts: 13
the use of tables is a very dangerous process. I have examples from actual field investigations and have found that the 70E tables can result in very serious injury and death. When you look at the medical cost alone you may be very surprised. In one incident one person's medical bills were at the $6M level and a second persons medical bills were at $1.5M. The six million dollar man spent 3 to 4 months in an induced coma had much of his body's skin replaced from that take from a cadaver. Lets face it, being penny wise and pound foolish can cost you plenty.

If you use tables and have the unfortunate experience of having someone severely burned based upon your use of tables you better be prepared to defend your choice. You may face me and I will definitely make you sweat. Its your choice.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Tue May 19, 2015 3:02 pm 
Offline
User avatar

Joined: Tue Oct 02, 2007 7:23 pm
Posts: 40
Location: Houston, Texas
It's amazing how ugly people are on this forum. The tables provide results just as accurate as SKM, ETAP or Easypower and definately better than 70E tables. Many NFPA and IEEE members have looked at my equations, methodology and given it the go ahead - encouraging me to submit to NFPA. What's wrong with saving the businesses money?


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Wed May 20, 2015 7:24 am 
Offline

Joined: Mon Nov 10, 2014 11:01 am
Posts: 13
My purpose is to point out the problems with using tables. First, the tables do not consider the available fault current from the utility. Next, the tables do not consider the transformer's impedance. Next, you have to do more than calculate two or three points of consider the trip time of an adjustable circuit breaker. And what about non adjustable circuit breakers? Do the tables take into consider a large motor at a long distance from its controller/overcurrent protection? I have found disconnect switches at large motors that have large incident energies which are larger then that of the controller & overcurrent protection. There are just too many variables to rely upon the table method.

My comments ended with the facts. Serious injuries can happen which often result in lengthy litigation. The "flashTables" take no responsibility for the results they produce. Read the fine print. So, if you use the tables are you prepared to defend the table method in court. Anyone doing arc flash risk analysis has to be prepared to defend their methods used. Which is the most defensible method?


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Wed May 20, 2015 1:57 pm 
Offline
User avatar

Joined: Tue Oct 02, 2007 7:23 pm
Posts: 40
Location: Houston, Texas
You are in fact very wrong. The utility data is considered in the calculation as well as transformer impedance and many other factors. This IP has been under development for over 8 years and is very exact in its methods. On our first industrial site of over 1000 points, only 1 label had a different PPE than the ones being removed (from past SKM study). The 1 that was different - we had a more conservative result. I really think you need to study up more on the standards... especially manufacturing and code standards. The input received on this was from Phd level electrical engineers and subject matter experts in the field of engineering calculations and electrical safety that serve on committees and consult world-wide. I can't believe your statements and your "threat" of law suit and negligence.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Wed May 20, 2015 2:23 pm 
Offline

Joined: Mon Nov 10, 2014 11:01 am
Posts: 13
I looked at the sample pages and I didn't find any place where utility information was considered along with transformer impedance. I also like the disclaimer on the product. The product takes no responsibility for the accuracy and validity of the results. If they product was so good why do you completely back away from any claims of accuracy, etc.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Wed May 20, 2015 2:26 pm 
Offline
User avatar

Joined: Tue Oct 02, 2007 7:23 pm
Posts: 40
Location: Houston, Texas
I copied most of the disclaimer directly from the IEEE 1584 spreadsheet that comes with the standard.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Fri May 22, 2015 8:59 am 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1806
Location: North Carolina
I looked at your tables. Yes they have transformer impedance. I actually looked.

First off, let's start with a simple issue. Are your equipment tables better than the ones in 70E? I would have to say yes. Are they better than IEEE 1584? I would emphatically say no.. In my mind, the real question is that if I did not have a complete and detailed power system analysis, would I be better off with:
1. NFPA 70E tables.
2. Michelle Murphy's tables.

I would have to say Michelle's tables seem to overcome some of the limitations of the 70E table. Its not perfect but with almost no information to work from, it should give better estimates for more cases whereas 70E relies on being able to accurately estimate breaker opening time which is impossible without a level of information that would then allow us to use IEEE 1584 anyway.

If however the question is what is the best method, that is a little more debatble and goes like this:
1. Actually testing...Accuracy=100%. Cost = high.
2. Wilkin's time-series analysis method. Numerical accuracy = +/-2%. Should be similar to IEEE 1584 costs but Wilkins didn't release full details on his model to be able to duplicate it.
3. IEEE 1584...numerical accuracy +/-5%.
4. Lee...numerical accuracy varies from +/-10% to +/-300%+ and error grows with voltage/current.
5. 70E or Murphy's tables...accuracy is variable depending on equipment details.

When compared this way, actual testing wins hands down followed by Wilkins followed by IEEE 1584. So in this regard, the two tabular methods are not in the running. It would be a mistake to compare either one to IEEE 1584 except in a very semi-quantitative way.

A number of statements from Michelle in an offline E-mail (sorry I didn't ask but I feel these are relevant) fill in some details about the Arc Tables:

"We considered two things and not an infinite bus (not reasonable). For calculating high incident energy we assumed 250kA, which should cover motors that will instill inrush (large motors have soft-start or drives). On the low end we considered much lower bolted fault current, to get reasonable results for arcing current when time delay is affected as it is so low."

So it's not infinite bus but it's still ridiculously high. Utility equipment is hard to get that goes over about 20-30 kA so 250 kA is certainly "ridiculous" enough on the high end and none of the testing that I'm aware of extended beyond about 20-40 kA anyways. Not sure what the "low end" consideration is though because this was never explained.

The tables assume standard (ANSI) impedance. On the low end this is generally followed but once you get into the realm of "custom" built (generally over about 2500-3750 kVA), transformers impedance tends to increase. As they grow this actually becomes desirable to keep equipment costs in check (again, 20-40 kA is something of a "barrier"). Response was:

"The variations on transformer impedance are not a major factor. It yields small differences, which in some cases could lead to a higher level with SKM. This is reasonable as if you correctly gathered all the information and modeled it with SKM or ETAP, etc. Here’s why - the IEEE 1584 equations are estimates, the true physics equations are unknown. NFPA 70E tables are estimates. Spending money gathering every cable size and it’s length, etc. is silly to me because you still have an estimate. My method is as accurate an estimate as anyone else’s. Look at fixed trip breakers - obviously each time the values are with the smaller arcing current and increased time delay. Is there another section in the tables where this is not true (let me know where so I can take a look). Also, if you have the 12 curves for typical fixed trip breakers I would be willing to analyze those. We used the NEMA Standard AB 3-2013, Page 31, Figure 5-3, Typical Time-Current Curve for a circuit breaker with fixed instantaneous thermal-magenetic trip system."

Which is interesting but ignores the fact that the worst arc flash results are generally right close to the secondary side of transformers and are definitely not "insignificant". The difference between a 1500 kVA transformer and a 2500 kVA transformer at ANSI impedance is the difference between <40 cal/cm^2 and >40 cal/cm^2 but once you get some distance away from it (say 100 feet), it is no longer over 40 cal/cm^2. So I'd be inclined to disagree. On a positive note although NEMA AB-4's table is nowhere near UL 489 or ANSI or IEC tables for breaker response curves, it is extremely conservative and serves the purpose.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Fri May 22, 2015 10:11 am 
Offline

Joined: Mon Nov 10, 2014 11:01 am
Posts: 13
Nice discussion of the issues. My problem is too many people represent the table methods as being just as good as doing a full arc flash study. I have real trouble with that. One speaker at the 2015 National electrical Safety Workshop in Louisville, KY this past January first insinuated that the Table method was just as good as calculations and then stated that the main objections to the table method comes from engineers because they won't make as much money by using the table method. That presentation resulted in a formal complaint to the chair of the workshop.

That kind of statement is highly insulting to me as I am an engineer.

I have also looked into developing a table method or simple calculation to be used by electricians before working in a facility where a study has not been preformed. I just have not had the time to do enough research. I also have a problem where arc flash training is minimal as I have seen the results; $6M in medical bills.

I quickly reviewed the Arc Table sample but would have liked to test a more difficult example. At a $1000.00 to satisfy my interest I guess I am just not that interested in a test.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Fri Aug 21, 2015 11:35 am 
Offline
User avatar

Joined: Tue Oct 02, 2007 7:23 pm
Posts: 40
Location: Houston, Texas
I have some good news on the testing front. We compared an SKM study with over 2,000 unique points to our tables. The PPE levels matched 100% of the time, however, the existing settings had most breakers set high. There was quite a bit of variety in terms of design and age of the equipment as the plant has been had on-going changes over the last 10-20 years.

Right now, a large company with over 100,000 points is doing some of this comparison too. While I don't expect the results between software studies and the tables to match 100% of time, we are expecting good results, and perhaps a few tweaks to the tables.

The real benefit of this method is the billions in industry savings. I'm not sure how one can claim that one method is more accurate than another. For example, are software data entry folks considering breaker testing results to make sure their TCC curves align 100% with field actuality, etc. I see lots of shortcuts being made by data collectors, and lots of assumptions that aren't always based on common sense. There is a reason the IEEE 1584 has a big disclaimer in their standard. There is also a reason they plan on updating the equations and continue to do research. Plasma physics is something I explore on my own time... it is a new field full of uncertainty.

Sometimes I think engineers who are doing these studies or promoting these studies at a high cost no matter what, have deluded themselves. The company with over 100,000 points was looking at paying 10-30 million dollars just to get the study and labeling done. Then they were going to have to staff an engineer to keep up with the model. What the hell?

-Michelle


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Fri Aug 21, 2015 2:31 pm 
Offline
Arc Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 679
Location: Rutland, VT
mnmurphy wrote:
Sometimes I think engineers who are doing these studies or promoting these studies at a high cost no matter what, have deluded themselves. The company with over 100,000 points was looking at paying 10-30 million dollars just to get the study and labeling done. Then they were going to have to staff an engineer to keep up with the model. What the hell?

-Michelle


Well let's not jump the gun here. There are many benefits to doing a study that a table method will not yield. To name a few:

1. Development of a one line diagram based on the field walkdown for data collection. Many facilities do not have a one line.
2. Identification of some NEC violations such as overcurrent protection for conductors
3. Equipment overduty issues
4. Coordination study including TCCs
5. Ability to identify strategies to reduce the incident energy levels.
6. Goes along with #3 but the short circuit current available at that device

Just a few that come to mind.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Support Public Input 130 - Commercial Tables for Arc Fla
PostPosted: Fri Aug 21, 2015 3:05 pm 
Offline
User avatar

Joined: Tue Oct 02, 2007 7:23 pm
Posts: 40
Location: Houston, Texas
Barry,

I agree with you. But my statement said "no matter what". For my existing client that had 100% matching labels, we also collected data during the labeling process and did a short circuit, load flow and coordination. They had never had a load flow done and we found issues, and the coordination study they had done 5 years ago was never implemented (probably familiar to you all who do studies...). We redid it due to 25% growth in the plant or would have recommended just a review of the past study at very little cost. For each of my clients, we offer full engineering services, along with a world-class maintenance program and various training - we are always looking for more partners to work with that offer high quality goods.

What I am saying is that some companies are interested in arc flash and electrical safety and are often being oversold a bill of goods, or do not even understand and comprehend what they are getting. In fact, most of my customers are finding they are not compliant in-between audits despite the high costs they are paying every 5 years for these studies.

I think Flash Tables has value. While I encourage some of my clients to pursue additional engineering at a higher cost, it isn't required by NPFA 70E and it often isn't needed all that much. Especially in the commercial sector, where compliance is still low. I wish the businesses and engineers who find my idea insulting, indecent and unimportant, would understand that I still value what they do.


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 15 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