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 Post subject: Properly Labeling Electrical Equipment Can Prevent Arc Flash
PostPosted: Tue Oct 21, 2014 10:31 am 
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Joined: Tue Oct 02, 2007 7:23 pm
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Location: Oak Ridge, Tennessee
This simplified method to label electrical equipment includes accurate arc-fault values and is a cost-effective way to reduce arc flash hazards. See the link to EHS Today for the article.

http://ehstoday.com/safety/properly-lab ... -workplace


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Tue Oct 21, 2014 11:31 am 
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I personally don't really like the idea of an electrician using the tables to make the labels, if it can be helped. It should only be a stop gap method until a proper arc flash study can be done.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Wed Oct 22, 2014 9:25 am 
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mnmurphy wrote:
This simplified method to label electrical equipment includes accurate arc-fault values and is a cost-effective way to reduce arc flash hazards. See the link to EHS Today for the article.

http://ehstoday.com/safety/properly-lab ... -workplace


Mnmurphy, my understanding is you are associated with R. E. Henry PE LLC? I have researched your website at http://www.arcflashtables.com but I could not find any detailed information about the table method. The EHS Today article, you make reference to, claims the method is based on detailed analysis of electrical distribution systems, all the equipment sizes and their combinations have been calculated for the label requirements, and the analytical results have been compiled in the tables. It simply sounds to good to be true.

Could you please share with the forum community the information about how you have come up with the values and send us a sample of your tables?


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Wed Oct 22, 2014 9:57 pm 
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If you go to the website and go to REQUEST TABLES there is a sample of our 480V tables for viewing. Things other than that require a NDA to be signed. I am willing to answer some questions on the forum though.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Thu Oct 23, 2014 6:59 am 
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mnmurphy wrote:
If you go to the website and go to REQUEST TABLES there is a sample of our 480V tables for viewing. Things other than that require a NDA to be signed. I am willing to answer some questions on the forum though.


I went to view the sample tables but the display was to small to read. Is there a larger version?

I would be interested in testing the results of the tables against a model based on IEEE 1584 equations as I think other forum members may interested in also. Would you be willing to take some simple models from forum members and post side by side comparisons of results using your tables and the model results?


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Thu Oct 23, 2014 11:36 am 
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mnmurphy wrote:
If you go to the website and go to REQUEST TABLES there is a sample of our 480V tables for viewing. Things other than that require a NDA to be signed. I am willing to answer some questions on the forum though.


I've looked into the arc flash tables user guide available for download on your website and I didn't have to go past page 10 to realize you may have got it all wrong. As an example, a quick look on Table 2.1.0 reveals that arcing current is calculated based on transformer KVA rating and feeder length alone.

Image

As far as I can see, the Table 2.1.0 data is based on numerous assumptions such as:

* Infinite buss.
* Transformer with a particular percent impedance value.
* Single feeder of a particular gauge.
* Branch circuit impedance between main breaker and arc fault any where down the line is 0 Ohm and has no impact on arcing fault current coming from the source and through the main breaker.

Questions:

1. How source impedance value is factored-in in arcing current data published in Table 2.1.0?
2. How actual transformer percent impedance is taken into account in arcing current published in Table 2.1.0?
3. How actual feeder impedance and number of feeders in parallel is reflected in arcing current data published in Table 2.1.0?
4. How does the table 2.1.0 accommodate branch circuit impedance between main breaker and arc fault XXX ft. down the line?
5. Out of curiosity, who (name and title pls.) put these tables together?

I hope no NDA need to be signed before you or your company representative can answer the questions above.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Thu Oct 23, 2014 5:30 pm 
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I was able to read the document and got to page 10. Here are my questions:

The Example starts at the low side of a 500kVA transformer and provides a description of the conductors into a panelboard. A rather vague statement is made about "Entering Table 2.1.0, the arc-fault current is the average of 4.3kA to 4.8ka, read from 300 and 500 feet." With no reference to available fault current, transformer impedance, and conductor size, material, insulation, how is this arc fault current arrived at?

There seems to be quite liberal assumptions made in the example about the breaker trip settings and the Table 2.1.0 in the sample is blank with no values.

Again, it would be most interesting to hear details on how this method was developed, how the arcing fault currents were arrived at and side by side comparisons of this method with actual studies.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Fri Oct 24, 2014 8:25 am 
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The assumptions for the calculation are proprietary and require an NDA to see. However, we do carefully consider the fault current under various scenarios; for adjustable trip breakers we use a conservative value of 250kA (an infinite bus for determining incident energy would be too conservative) and 3x the transformer rating for arcing current determination (lower more conservative result). The same type of factors weigh in to choosing PVC vs steel, etc. always choosing the most conservative although these values do not differ the results much. Anyone willing to sign the NDA and compare our method to the traditional software - we could publish your results here. The biggest assumption in our calculation is the use of the IEEE 1584 equations, which are not the true physics equations for arc flash, but estimated values that are soon to be improved, but not perfect.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Fri Oct 24, 2014 9:25 am 
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mnmurphy wrote:
The assumptions for the calculation are proprietary and require an NDA to see. However, we do carefully consider the fault current under various scenarios, an infinite bus for determining incident energy and 3x the transformer rating for arcing current determination (lower more conservative result). The same type of factors weigh in to choosing PVC vs steel, etc.


Assumption is the mother of all screw ups. And your method seems to make way too too many assumptions. Thanks for letting me know you are assuming an infinite bus. That assumptions alone proves your method is wrong.

Regarding your NDA comment, you have not come to this forum to advertize your product, have you? If you want to get third party opinion about your product or service you should be ready to share all the information about it.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Fri Oct 24, 2014 10:52 am 
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The tables give the same answers as using software. It is not an infinite bus we are using for adjustable trip breakers. It is 250kA for determining incident energy which is conservative and 3x the transformer rating for determining arcing current to develop time delay. This is a good method and we support it. The arc flash equations are estimated data as put out by the IEEE and not the true physics equations for arc flash. The NFPA 70E method provides different results. Our tables are accurate and just as accurate as any other method. Impedance and other assumptions are all conservative and don't affect the results to much of any degree. I challenge someone to sign the NDA and do a comparison against one of their studies. I would be willing to publish the results.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Fri Oct 24, 2014 10:56 am 
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For adjustable trip breakers we do not use infinite bus. For determining incident energy the higher the kA the more conservative the result. Therefore, we used 250kA for source for determining incident energy. For determining arcing current and time delay, we use 3 x the transformer size which is a good estimate. The IEEE 1584 equations are estimated values, not the true physics equations - that is why the NFPA 70E table values are different but still legal. I challenge anyone to sign our NDA and test our tables against the software. We can publish the results here. All other assumptions are conservative.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Sun Oct 26, 2014 11:09 pm 
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I'd like to open source the technology, and if I share the IP here that is exactly what I would be doing. I would give up all my IP rights as an inventor. It depends if I can keep a business afloat by open sourcing. In the meantime, if someone wants to be a "third party tester" we can sign an NDA and move on. I wouldn't downplay a business that needs to protect IP to stay in business. We share our validation with all our clients. No one hear seems to be recommending any clients, only complaints and desiring free rights to IP that could put me out of business.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Mon Oct 27, 2014 8:51 pm 
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I have shared the information about it. It is accurate. And we don't use an infinite bus for adjustable trip, or for medium voltage or for generators. You can't assume I made too many bad assumptions without looking into it further.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Thu Oct 30, 2014 2:42 pm 
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As some people may be reluctant to sign a NDA, would you be open to someone posting a model similar to what an electrician would develop for your system and then have you post the results of your system. The party that posted the sample could then post their results. This way no one would have access to your proprietary system but could see the results.

What I am thinking is a pdf attachment of a sketch of a small electrical system with breaker/fuse data, transformer data, conductor data, etc. Since there are quite a number of facitlities that do not have a one line, it would be the electrician sketching it out and collecting the data.

Would this be acceptable to you? It would be interesting to see a couple models done.

Other readers - would anyone be willing to submit a small model?

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


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Thu Oct 30, 2014 8:02 pm 
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mnmurphy wrote:
I have shared the information about it. It is accurate. And we don't use an infinite bus for adjustable trip, or for medium voltage or for generators. You can't assume I made too many bad assumptions without looking into it further.


I'm a bit confused with your statements. Your earlier post stated "an infinite bus for determining incident energy is assumed". Then, the message was edited and the original statement was changed to read "for adjustable trip breakers we use a conservative value of 250kA (an infinite bus for determining incident energy would be too conservative)". Now again you say "we don't use an infinite bus for adjustable trip, or for medium voltage or for generators". All that put aside, if you are not using an infinite bus, why would you use specifically 250kA bus and not more commonly found lower KA values? Also, have you realized that the IEEE 1584 method is applicable to systems with maximum 106kA available short circuit current.

I don't also understand why and how using 3x the transformer rating for arcing current determination results in "lower more conservative result". In fact, using 3x the transformer rating would result in up to 3x available short circuit current value and roughly up to 3x arcing current value.

I have more questions to ask but I'll let you address first the questions I asked you before.

Also, I don't quite understand what you've invented. Have you invented IEEE 1584 equations? A table? The 250kA bus assumption, 3x the transformer rating, any other assumptions used in putting the table together? Please clarify.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Tue Nov 11, 2014 7:35 am 
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I just don't get it.

To use the IEEE 1584 equation, we need three things:
1. Working distance, equipment design, gap distance, grounding type, etc. These are all equipment and somewhat task specific values that are given in tabular form in IEEE 1584 already.
2. System voltage. Generally this is known and somewhat standardized. Again, this can be tabular.
3. Fault current and opening time. These are the tricky parts because the nature of the protective devices is to cause them to be inter-related. Fault current can be roughly upper-ended using some relatively simple formulas such as those in the ANSI standard for calculating bolted fault currents (within limits) but the consequence if a trip curve is used is that the opening time will be unrealistically short. A maximum opening time of 2 seconds is suggested by IEEE 1584 but forcing all cases to use this value will result in unrealistically high incident energy values. I think the assumption that arcing current is no less than 3 times the maximum operating current range is not unrealistic (NEC 430 recommends 350% setting for dual element fuses for motor loads) but I'd be reluctant to take a leap of faith to assume that this works in all cases and I would be looking at load currents, not transformers.

Also, 250 kA? What in the world? I have never seen a value that high show up anywhere on a study. That sounds to me like an "infinite bus" even if it's not truly infinite. I don't think I recall seeing equipment ratings higher than 100 kA. 480 V equipment can get pretty high and 65 kA ratings are not that uncommon but 250 kA? That doesn't pass the smell test.

So...I'm curious on the last step, item #3. Without requiring an NDA you could probably document a simplifying approach to estimating arcing current and opening time by itself. The rest of the content might be straightforward to recreate (or not), but it will not be controversial either.


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 Post subject: Re: Properly Labeling Electrical Equipment Can Prevent Arc F
PostPosted: Wed Dec 17, 2014 10:41 pm 
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Location: Oak Ridge, Tennessee
The Flash Tables Unlimited (www.arcflashtables.com) will be open sourced in mid-January. Then you can download the full tables and the validation spreadsheet.


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