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 Post subject: Labeling Multiple Sites with a "Worst Case"
PostPosted: Wed Feb 14, 2018 3:08 pm 

Joined: Mon Nov 27, 2017 12:07 pm
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I have a client with more than 900 outdoor sites that consist of a pole top utility transformer (120/240V) of unknown size and impedance, a service disconnect, and one piece of electrical equipment. Based on experience and information provided to us, we gave them a chart of IE's based on typical transformer sizes and impedance with an arcing duration of 2 seconds because we do not know the OCPD. The client is satisfied with the worst case IE and they are willing to certify that none of their systems are outside of the simulated scenarios.

Now, they want us to produce 900+ labels with the highest calculated IE for them to put on all the sites. We believe that the IE must be calculated with site specific information, however the client refuses (understandably) to get information from 900 sites. We are comfortable that there is no site with a higher IE than what we calculated, however we think we are violating the code by not publishing the lower IE from the calculated site specific information.

Does anyone have any experience with a similar situation or any guidance on this topic?


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 Post subject: Re: Labeling Multiple Sites with a "Worst Case"
PostPosted: Thu Feb 15, 2018 5:59 am 
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Location: Rutland, VT
From the description, it seems like it is one single phase transformer? Can you clarify?

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 Post subject: Re: Labeling Multiple Sites with a "Worst Case"
PostPosted: Thu Feb 15, 2018 6:32 am 

Joined: Mon Nov 27, 2017 12:07 pm
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Yes, they are single phase transformers. Each site (900+ sites) are served by a utility transformer that is not necessarily dedicated (it may be serving homes, farms, etc.)


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 Post subject: Re: Labeling Multiple Sites with a "Worst Case"
PostPosted: Thu Feb 15, 2018 7:39 am 
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Joined: Mon Jan 18, 2010 11:35 am
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Location: Wisconsin
CDEE wrote:
... not publishing the lower IE from the calculated site specific information.


There is no 'code' requirement that the arc flash incident energy (AFIE), on a label, needs to be anything different than what is required for the employee to be able to choose the appropriate PPE.

Site specific labeling needs to conform with the employer's ESWP procedures.


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 Post subject: Re: Labeling Multiple Sites with a "Worst Case"
PostPosted: Thu Feb 15, 2018 9:00 am 

Joined: Mon Nov 27, 2017 12:07 pm
Posts: 6
If the AFIE was not calculated specifically for that equipment, would it not violate the labeling requirements 130.5(H)(3)a. "Available incident energy and the corresponding working distance... for the equipment"

Although, if I have done a risk assessment by calculating the worst case AFIE, I suppose I could publish the minimum arc rating of clothing or, apparently, the site-specific level of PPE as outlined in our client's ESWP.

At this point, my AFIE calculations are informing the clients ESWP.

I'll buy it, thanks. This is new territory for me because we have always published the AFIE calculated for a specific piece of equipment on the the labels.


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 Post subject: Re: Labeling Multiple Sites with a "Worst Case"
PostPosted: Thu Feb 15, 2018 10:26 am 
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Location: Rutland, VT
How are you calculating arc flash for a single phase system?

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 Post subject: Re: Labeling Multiple Sites with a "Worst Case"
PostPosted: Thu Feb 15, 2018 10:54 am 

Joined: Mon Nov 27, 2017 12:07 pm
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SKM uses 1584 for single phase systems. Obviously the results are conservative, but our client specifically requested we use 1584 for single and three phase systems knowing the limitations of the 1584 equations.


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 Post subject: Re: Labeling Multiple Sites with a "Worst Case"
PostPosted: Fri Feb 16, 2018 9:27 am 
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Location: North Carolina
Nothing in 70E or IEEE 1584 restricts you from putting a value on the label that exceeds the actual value. In fact this is inherent in the table based approach and inherent in the concept of providing "conservative" results from an engineering ethics point of view.

But more importantly it also makes it possible to have a "stock" label system. If you simply choose thresholds that correspond to the PPE that is available for use then this makes the "stock" label approach possible and practical. For instance you could have one label for say 1.2, 4, 12, 40, and 100 cal/cm2 which mirrors typical utility PPE. Does this sound suspiciously like PPE Levels 1, 2, 3, 4, or the similar ranges given by NESC? Yep...both the NESC and NFPA 70E not only support but use discrete "levels" of PPE in their own table-based approach. All that you are developing is a customized table based approach for that customer. Nothing wrong with that at all.

This is actually the best approach when it comes to utilities. Due to the fact that there are hundreds to thousands of work sites, equipment is very fluid and network configuration frequently changes, and very long line lengths, it is impossible to do the sort of "point-to-point" model approach that SKM, ETAP, etc., are specifically designed for. In a utility environment an arc flash study is just that...more of an engineering approach to determining arc flash results over a large area. Power system software becomes a tool for doing the estimates but by itself it simply isn't practical to use it over a large area because it isn't designed for this distributed approach.


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 Post subject: Re: Labeling Multiple Sites with a "Worst Case"
PostPosted: Fri Feb 16, 2018 9:38 am 
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Joined: Tue Jan 13, 2009 5:00 pm
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If using the worst case from 900 sites for all 900 were a violation, then so would using the three phase IE for a single phase system.

Suggest looking at the intent. Unless worst case causes PPE selection that causes other hazards of visibility and heating (seems unlikely here), then the intent is satisfied.


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 Post subject: Re: Labeling Multiple Sites with a "Worst Case"
PostPosted: Mon Feb 19, 2018 9:41 am 
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Joined: Fri Apr 15, 2011 7:43 am
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Location: Colorado
You might look at the NESC Table 410-1 to see if you can take advantage of that???


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 Post subject: Re: Labeling Multiple Sites with a "Worst Case"
PostPosted: Tue Feb 20, 2018 6:36 am 

Joined: Mon Nov 27, 2017 12:07 pm
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Thanks everyone for the insight. The reason we are staying away from the table method is that we have a DC component that is below 100VDC - outside the rage of 130.7(c)(15)(b). I am taking a closer look at NESC 410-1, thanks for the tip.


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 Post subject: Re: Labeling Multiple Sites with a "Worst Case"
PostPosted: Thu Feb 22, 2018 11:36 am 
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I'm not sure about a DC "component" but see this:

http://efcog.org/wp-content/uploads/Wgs ... 40714e.ppt

The data is available in a Battcon paper that I'd have to track down.

Suffice to say that you have to get down to under 1/4" with in excess of 20 kA of available fault current to sustain an arc for 0.08 seconds which works out at 18" to right close to 1.2 cal/cm2. In a utility setting with OSHA 1910.269 you'd reduce this to 15" working distance but the threshold is now 2.0 cal/cm2 so I don't think you'd exceed the threshold requiring arc flash PPE and this is at 130 VDC. Unless your conditions exceed those, you don't have an arc flash hazard. But your terminology said "DC component". This means that on say the positive direction we'd have AC peak + 100 VDC and in the negative direction it would be AC peak - 100 VDC. The net effect would be the same as an AC fault. As far as I know nobody is attempting to model the DC transient during the initial fault at the first couple cycles and there is basically no research or anything else to apply to this mixed voltage condition.


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