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 Post subject: Arc Flash Labeling - Feeder Bus Duct
PostPosted: Tue Aug 06, 2019 10:07 am 

Joined: Sat Sep 23, 2017 3:15 pm
Posts: 7
Hello everyone,

I have a question pertaining to arc flash labeling of feeder bus duct. I have a main distribution panel at 480V that has two 600A breakers. Both breakers feed (2) sets of (3) #350 KCMIL copper that feed over to a 600A bus duct run. My question is how do you provide labeling for the bus duct in this scenario? On previous projects I provided a label every 15-25 feet with the bus duct "worst case" label. The maintenance supervisor is asking for a label at each bus plug, which there are over a hundred on this project. This seems to be time consuming and expensive. If anyone has ever dealt with this issue when doing an arc flash evaluation, please let me know how you provided the labeling.

Best Regards,
Engineer in Training


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 Post subject: Re: Arc Flash Labeling - Feeder Bus Duct
PostPosted: Wed Aug 07, 2019 9:39 am 
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Joined: Mon May 25, 2015 1:17 pm
Posts: 16
Location: Northern California
I would not label a feeder bus duct as it is not normally accessed (covers removed) energized. But yes the plugs would need labels and I would normally label them for the line side.


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 Post subject: Re: Arc Flash Labeling - Feeder Bus Duct
PostPosted: Wed Aug 07, 2019 5:23 pm 

Joined: Sat Sep 23, 2017 3:15 pm
Posts: 7
Hmm, interesting. From what I read, the common practice for power systems studies is to determine the worst case arc flash hazard on the bus duct which is usually at the end of the bus duct run and apply arc flash labels every 20-30 feet. I have not had any customers ask to label the busway with multiple incident energy values because this can become very confusing, especially given the length of the bus duct run and the amount of bus plugs we have on this project. Our policy is to recommend to use the worst case for the run.


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 Post subject: Re: Arc Flash Labeling - Feeder Bus Duct
PostPosted: Mon Aug 12, 2019 8:27 am 

Joined: Mon Dec 07, 2015 9:45 am
Posts: 33
Location: Massachusetts
We provide labels for each bus plug (and future plugs) to be labeled. Sometimes the customer will pay us to place the labels, sometimes they will do so themselves, because, as you mention, it is very costly for them to pay someone if they have people that can do that).

When the bus has enough plugs labeling the bus itself is not necessary, but I could make the case that the bus, or its plugs, should have a visible label every ~25ft so if someone were to be adding a new plug while the bus is energized they would see what the incident energy level is in performing that task.


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 Post subject: Re: Arc Flash Labeling - Feeder Bus Duct
PostPosted: Mon Aug 19, 2019 8:00 am 
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Joined: Tue Oct 26, 2010 5:00 pm
Posts: 195
Location: Maple Valley, WA.
We will calculated the AF energy and provide a label for any bus plug that has a circuit breaker or fused disconnect installed. This is a good compromise because you are only adding locations that have a breaker or disconnect that may be worked on while energized. If a new plug will be installed in the future, then go the closest downstream plug that has a breaker or disconnect and assume the energy level is the same. Then when the 5 year AF Study refresh is performed, include this new switch in the model and calculate the correct energy level.

_________________
Robert Fuhr, P.E.; P.Eng.
PowerStudies


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 Post subject: Re: Arc Flash Labeling - Feeder Bus Duct
PostPosted: Mon Aug 19, 2019 10:22 am 

Joined: Mon Nov 10, 2014 11:01 am
Posts: 22
I model busducts using one of two methods.
1. Break the busduct into segments say 50' and model groups of motors at each break point. then determine the worse case.
2. build a detailed model of the busduct and calculate the IE at each tap.

Labeling busduct taps is a problem and a waste of time. Normally you can't read the label from the ground. Next I make charts to be installed at key locations in the plant.

My newest thought is to make a large sign that can be hung from the busduct. The sign needs to be easily to read from the ground.

Also, when considering a person working in a high lift, they have no means of escape. So you probably want the maximum arc time extended out from 2 seconds.


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 Post subject: Re: Arc Flash Labeling - Feeder Bus Duct
PostPosted: Tue Sep 17, 2019 6:58 am 

Joined: Fri Sep 28, 2018 7:32 am
Posts: 13
Location: Sioux Falls, SD
We have a large customer with more than a hundred bus ducts making use of approximately 2,500 bus plugs. We analyze every 10' section of bus duct and label every bus plug installed on a section with that sections IE. They have several double fed bus ducts as well where a feed from one sub-station feeds one end of the duct while the other end is fed from a different sub-station. Often times the arc flash level is the same throughout all sections of the bus duct. We have found several though where there are "bad" spots and one or a couple of sections will have a higher arc flash level than the rest of the bus duct. This does not seem to be consistently at one end or the other or in the middle. Due to the length of the duct as well as the affects of those which are double fed we find the "bad spots" to vary based on where the faults hit the OCPD's trip curve.


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