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 Post subject: 1910.269 Appendix E Table 3
PostPosted: Tue Feb 17, 2015 2:59 pm 
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Table 3 lists reasonable methods for selecting an incident energy calculation method. What I find interesting is that up to 15kV, IEEE 1584 is listed as a method for single phase and 3 phase open air open air arcs as well as 3 phase arcs in a box.

In the Overview, IEEE states that the applications cover an emperically derived model including enclosed equipment and open lines for voltages from 208V to 15kV. It further states that single phase systems are not included.

So, how can OSHA list IEEE 1584 as a recommended method for single phase arc in open air?

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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Tue Feb 17, 2015 8:27 pm 
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1584 is not directly validfor single phase. You just have to treat it as three phase knowing the results will be high. There are some suggestions of dividing by 3 out there but I don't believe there ks any support for doing so. I think some of the tests with phase barriers indicate that single phase arc incident energy is lower than 3 phase but not by a factor of 3. But with no rsearch for the right value, just using 3 phase results gives a conservative estimate.


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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Wed Feb 18, 2015 5:54 am 
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I guess another approach would be to determine the SLG fault current and use that as the bolted fault current in the IEEE 1584 equation.

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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Wed Feb 18, 2015 11:46 am 
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IEEE 1584 basically nullifies the single phase statement with the following taken directly from IEEE 1584 1.2 Purpose which states:

"Single-phase ac systems and dc systems are not included in this guide."

The new IEEE 1584 (when completed) will also not address single phase.


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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Wed Feb 18, 2015 12:03 pm 
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Thanks Jim. I guess the big confusion is why OSHA references IEEE 1584 for single phase open air when IEEE specifically states that it does not apply to single phase.

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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Wed Feb 18, 2015 1:54 pm 
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wbd wrote:
Thanks Jim. I guess the big confusion is why OSHA references IEEE 1584 for single phase open air when IEEE specifically states that it does not apply to single phase.


That's one of the many mysteries with the new 1910.269 Another one that I can't quite figure out is how Federal Law can reference a commercial product i.e. ArcPro.

Give's us things to ponder! :)


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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Thu Feb 19, 2015 5:31 am 
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Here is my thought on why OSHA referenced ArcPro. If one looks at the table, all the methods can be referred back to a standard or authors of a paper with equations which then can utilized in various software programs.

For the case of ArcPro, there is no readily available paper with equations that can be referenced and then used by other companies to develop software around those equations or a spreadsheet developed. I don't think OSHA had much of a choice except to reference a brand name.

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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Thu Feb 19, 2015 10:45 am 
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I agree. I have wrestled with the same issue over and over again. The choices for above 15 kV seem to be:
1. Use Lee. Of course it's wrong, and by a ludicrous amount. But it gives no upper limit on current or voltage.
2. Use NFPA 70E-2012 task tables. The stuff for 15-35 kV was deleted in the 2015 edition however. So this would be akin to using the 70E-2004 arc flash incident energy equation. So no longer an affective solution at this point.
3. Use Duke heat flux. Commercial software, not much explanation behind the calculation. OSHA doesn't like it. Seems like going out on a limb.
4. Use tables in NESC. Effectively, this is ArcPro at work but gives the appearance of following a standard. Only one problem and that is the note in the tables that states that it only applies to open air conditions. So can't be used on switchgear, which is where it is needed most.
5. Use the arc flash formulas developed via test work by EPRI. On the one hand they are very simple and get the job done. On the other hand, it is using an obscure piece of information that is not well known or referenced.
6. Use ArcPro. Yes, just turn your head and cough. I don't like it but since options 1-5 are not really practical at best, that leaves a single option. At least now it has the recommendation of OSHA.


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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Mon May 18, 2015 3:26 pm 

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I am curious if it is legal to provide a "comercially avaialble product" as the only approved methodology for complying with Arc-Flash calcualtions of over 15kV. It seems, if it couldn't be easily described in tables or calculation methods elsewhere that it should at least be left to the responcible parties on how we should comply. 1910.269 is a federal standard that essentially forces the public (well compliance engineering public) to purchase a specific product. It seems akin to telling the public that they must all purchase Ford Fusions in order to be in compliance with emissions requirements, or apple Iphones in order to be in compliance with FCC requirements. Rather than describing how to comply, and allowing the user to evaluate what to purchase, or develop.


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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Mon May 18, 2015 5:08 pm 
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JSNrunner wrote:
I am curious if it is legal to provide a "comercially avaialble product" as the only approved methodology for complying with Arc-Flash calcualtions of over 15kV.


The footnote (4) states that Lee is acceptable though overly conservative.

I'll leave the legality question to the lawyers.

JSNrunner wrote:
It seems, if it couldn't be easily described in tables or calculation methods elsewhere that it should at least be left to the responcible parties on how we should comply. 1910.269 is a federal standard that essentially forces the public (well compliance engineering public) to purchase a specific product. It seems akin to telling the public that they must all purchase Ford Fusions in order to be in compliance with emissions requirements, or apple Iphones in order to be in compliance with FCC requirements. Rather than describing how to comply, and allowing the user to evaluate what to purchase, or develop.


No purchase is required. Useable tables are in the appendix of the freely available 1910.269 standard.


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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Tue May 19, 2015 6:20 am 

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Footnote number 3 says that OSHA would except it as a methodology to indicate that the incident energy is over 2cal/ft, but that values are high and unrealistic. Which is supported by the fact they indicated an "N" - not acceptable, in the table when describing methods for calculating incident energies.

As for the tables, I agree they give some guidelines on allowable energies versus clearing times, however I would much rather calculate the incident energy to indicate that it is under 8cal (which is the protection that we require our electrical workers to wear) then check against the table... For example, At 17kV what if my maximum fault current is 7500A, that is inbetween two current values and sort of in the middle of the voltage range, It is pretty restrictive to assume I must clear in under 23 cycles. The worst case is right above a fault current level, for instance at 5005A forcing my system to clear in 23 cycles could cause settings which create nusance tripping issues.

I suppose I must purchase a commercially available software, however being required to support a private company by a goverment organization in order to prove compliance with a rule rubs me the wrong way.


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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Tue May 19, 2015 7:35 am 
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wbd wrote:
Table 3 lists reasonable methods for selecting an incident energy calculation method. What I find interesting is that up to 15kV, IEEE 1584 is listed as a method for single phase and 3 phase open air open air arcs as well as 3 phase arcs in a box.

In the Overview, IEEE states that the applications cover an emperically derived model including enclosed equipment and open lines for voltages from 208V to 15kV. It further states that single phase systems are not included.

So, how can OSHA list IEEE 1584 as a recommended method for single phase arc in open air?


...and, did anyone notice that when OSHA references IEEE 1584 it is listed as 1584b-2011 in most locations? The 2002 edition seems to only be referenced once and IEEE 1584b-2011 is referenced at most other locations. The significance? 1584b-2011 is only an amendment regarding some of the text of the original IEEE 1584-2002. 1584b-2011 is not the current standard which is still the 2002 edition.


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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Tue May 19, 2015 8:33 am 
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JSNrunner wrote:
Footnote number 3 says that OSHA would except it as a methodology to indicate that the incident energy is over 2cal/ft, but that values are high and unrealistic. Which is supported by the fact they indicated an "N" - not acceptable, in the table when describing methods for calculating incident energies. .


Actually, the word used in the footnote is "acceptable". Rather large difference between it and the word "except". Yes, I meant to refer to footnote 3 above rather than 4.

JSNrunner wrote:
...however being required to support a private company by a goverment organization in order to prove compliance with a rule rubs me the wrong way.


You must have really liked answering that insurance question on your 2014 taxes. ;)


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 Post subject: Re: 1910.269 Appendix E Table 3
PostPosted: Tue May 19, 2015 9:43 am 

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For some reason, the fact that there are multiple vendors with multiple products for insurance, doesn't bother me as much as requiring me to purchase one product from one vendor. But your point is well taken.


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