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 Post subject: Labeling Requirements
PostPosted: Tue Sep 10, 2019 11:23 am 

Joined: Tue Sep 10, 2019 11:14 am
Posts: 1
I am newly registered here, but fairly experienced in arc flash studies and calculations. Occasionally I will encounter a situation where the OCPD of the utility company is either non-existent, or its model and information is unavailable or unattainable. I had one situation where I was given OCPD information from the utility that turned out to be wrong. In another case, the utility fuse label was so weathered that it was completely unreadable. The utility did not want to replace it. Without a utility OCPD, the software I am using for arc flash modeling will not calculate an incident energy for the first bus (which is usually the main circuit breaker). How do I label that panel without a calculated incident energy? Does anyone else run into this problem?


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 Post subject: Re: Labeling Requirements
PostPosted: Mon Sep 16, 2019 7:08 am 

Joined: Tue May 29, 2018 8:19 am
Posts: 26
You (your client) typically has no control over the utility, so it should not be considered in your IE study. Your study should assume no OCPD on the utility source. IE at the line side of the main(s) main be limited by the 2-sec rule.

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 Post subject: Re: Labeling Requirements
PostPosted: Mon Oct 07, 2019 8:24 am 
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Joined: Tue Oct 26, 2010 5:00 pm
Posts: 184
Location: Maple Valley, WA.
This is a big issue and happens quite frequently.

However, we have found that the owner has better luck requesting and obtaining the information versus the consultant. This is because the owner is the utility's customer and they tend to want to serve their customers instead of helping out the consultant. We send the a partially filled out form to the owner who then forwards it to the utility.

This method does not always work but most utilities will provide either the actual OCPD installed or what should be installed. The majority of utilities have a table that lists what the OCPD should be based upon the transformer size and primary voltage.

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 Post subject: Re: Labeling Requirements
PostPosted: Tue Oct 08, 2019 2:46 pm 
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Joined: Sat Nov 21, 2009 10:23 pm
Posts: 103
Location: Ohio
I can usually get the fuse part number with a spotting scope. If that does not work, I use a slow cutout type expulsion fuse size at 175%.

More important is the transformer impedance if it is utility owned,. They would have you think every transformer in the world is 5.75%. There are usually work-arounds on this, but, if I am given 5.75 %, I typically know, they are guessing. I will than do scenario's at 5.75 plus and minus 7.5% of the 5.75.


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 Post subject: Re: Labeling Requirements
PostPosted: Thu Oct 10, 2019 6:46 am 
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Joined: Wed Jun 10, 2009 5:00 pm
Posts: 256
Location: Toronto
abinadi wrote:
Without a utility OCPD, the software I am using for arc flash modeling will not calculate an incident energy for the first bus (which is usually the main circuit breaker). How do I label that panel without a calculated incident energy? Does anyone else run into this problem?


not sure which arc flash analysis program you are using but I would expect you can apply IEEE 1584 two (2) seconds rule by manually specifying arc duration if OCPD information is missing. In case when it takes OCPD more than 2 sec to clear arcing fault, incident energy would be determined based on 2 sec arc duration cutoff. A screenshot below shows an example of it.

Image

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