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 Post subject: How to Label Multi-Door Industrial Control Panels
PostPosted: Fri Feb 13, 2009 2:07 pm 
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Joined: Wed Jan 28, 2009 2:19 pm
Posts: 72
Location: Georgia
I am doing an arc flash analysis at one of our manufacturing plants and would like to know how you all are handling situations similar to this...I have a 500 kva transformer (480v:380v) feeding an 800 amp main breaker inside a motor control panel. The panel is a single 6 door, free standing enclosure. There are no partitions separating the 6 different sections of the panel.

The IE on the line side of the main breaker is 32 cal/cm2 at a BF current of 7.6 kA and fault clearing time limited to 2 seconds. The IE on the load side of the main breaker is 0.5 cal/cm2.

My question is...should I label the entire 6 door panel as a cat 4 or could I label the main breaker section as a cat 4 and the other 5 doors as a cat 0? If there was an arc flash behind door #4, the cat 0 flash should not be strong enough to cause an incident on the line side of the main breaker behind door #1??? The vast majority of the energized work (diagnostics, resetting drives, etc) is done behind doors 2 through 6. How are you all handling this?


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PostPosted: Fri Feb 13, 2009 3:29 pm 
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Joined: Mon Jun 02, 2008 11:58 am
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Location: Charlotte, NC
JJH wrote:
I am doing an arc flash analysis at one of our manufacturing plants and would like to know how you all are handling situations similar to this...I have a 500 kva transformer (480v:380v) feeding an 800 amp main breaker inside a motor control panel. The panel is a single 6 door, free standing enclosure. There are no partitions separating the 6 different sections of the panel.

The IE on the line side of the main breaker is 32 cal/cm2 at a BF current of 7.6 kA and fault clearing time limited to 2 seconds. The IE on the load side of the main breaker is 0.5 cal/cm2.

My question is...should I label the entire 6 door panel as a cat 4 or could I label the main breaker section as a cat 4 and the other 5 doors as a cat 0? If there was an arc flash behind door #4, the cat 0 flash should not be strong enough to cause an incident on the line side of the main breaker behind door #1??? The vast majority of the energized work (diagnostics, resetting drives, etc) is done behind doors 2 through 6. How are you all handling this?


Is the entire panel within the AFB of the line side of the main?


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PostPosted: Fri Feb 13, 2009 8:04 pm 
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Joined: Thu Jan 10, 2008 8:49 pm
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Location: New England
Not sure from your explanation of the construction. You said there are 6 doors in one section but no dividers?

If there is communication, ie, open space, then you have to think in terms of the cubic enclosure size. The fact that there may be multiple doors of access don't matter.

If there is seperation, ie, like one metal box stacked upon another metal box, and there if a reasonable expectation that the deflagration from the arc flash box, won't cause a fault in the adjacent box, then you can treat them as seperate entities.


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PostPosted: Mon Feb 16, 2009 6:21 am 
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Joined: Wed Jan 28, 2009 2:19 pm
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Location: Georgia
It is a single enclosure with 6 doors. The entire enclosure is within the AFB of the line side of the main breaker. However if an electrician is diagnosing a problem behind door #3 (2 doors from main breaker) and an arc flash occurs, the Cat 0 flash (calculated from the load side of the main breaker) that happens at door 3 will not be forceful enough to reach the line side of the main breaker at door #1.

If someone is working behind door #1 which contains the main breaker, then the entire enclosure is within the AFB because of the Cat 4 AF calculated from the line side of the main breaker. However if someone is working behind any other door, the the AFB is <1' because the Cat 0 AF is calculated from the load side of the main breaker.

Is it possible to have a single, multidoor enclosure labeled with different IE's?


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PostPosted: Mon Feb 16, 2009 7:57 am 
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To begin, The AFB only comes into play when the door is open. Except for high energy switch, like switchgear, you are not required to respect the AFB when there are no 'exposed' engized parts. While your parts are energized, they are not exposed when the doors are closed. So don't confuse the AFB as beingin conflict because they have two seperate values.

Yes, you can label each door with a seperate label. If we are dealing with a MCC lineup, lets say 10 sections wide, each section with 6 buckets, you would then need sixty labels. Most people are not doing that, they are installing one label on the top of every third section.

What you want can be done with six individual labels, but you need to take extra effort that personnel understand what you are doing.. Human nature says that if I walk up to a lineup and I read four labels all at PPE1, then I might assume the others are all the same since they are in the same lineup. So just cover this in your training.


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PostPosted: Mon Feb 16, 2009 8:04 am 
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Joined: Mon Jun 02, 2008 11:58 am
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Location: Charlotte, NC
haze10 wrote:
To begin, The AFB only comes into play when the door is open. Except for high energy switch, like switchgear, you are not required to respect the AFB when there are no 'exposed' engized parts. While your parts are energized, they are not exposed when the doors are closed. So don't confuse the AFB as beingin conflict because they have two seperate values.


I disagree with that statement, unless the equipment in question is Arc Rated Equipment it can pose an arc flash hazard with the covers on, the 2009 70E address this and so do the tables.


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PostPosted: Mon Feb 16, 2009 11:49 am 
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Joined: Wed Jan 28, 2009 2:19 pm
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Location: Georgia
In the case of a panelboard with a main breaker, we calculate the IE based on the line side of the main breaker. This is because if an arc flash were to occur on the load side of a branch breaker (usually lower energy), the combustible gases or shapnel that were created could also cause a secondary arc flash on the line side of the main breaker (usually higher energy). We want to be conservative and label for the worst case scenario.

However in a 12' long industrial control panel, I don't believe a Cat 0 arc flash would cause a secondary arc flash on the line side of the main breaker which is located 2 to 12 horizontal feet away inside the same enclosure.

I guess it would seem that as long as the line side of the main breaker (behind door #1) was outside of the arc flash boundary for an arc flash occuring behind doors 2 through 6, then door 1 could be labelled Cat 4 (as calculated at the line side of the main breaker) and doors 2-12 could be labelled Cat 0 (as calculated at the load side of the main breaker).

I understand that some people label the individual buckets of an MCC with different IE's. Has anyone ever labelled the different doors of an industrial control panel with different IE's? Haze10 is correct. If this is done, it must be well covered and documented in the training.


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PostPosted: Thu Nov 26, 2009 8:34 am 

Joined: Mon Dec 08, 2008 7:13 am
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Location: Quebec, Canada
JJH wrote:
In the case of a panelboard with a main breaker, we calculate the IE based on the line side of the main breaker. This is because if an arc flash were to occur on the load side of a branch breaker (usually lower energy), the combustible gases or shapnel that were created could also cause a secondary arc flash on the line side of the main breaker (usually higher energy). We want to be conservative and label for the worst case scenario.


That's something I'd like to know more about.

Is there any litterature about that or is this simply one more way to be conservative?

Any test or known events?


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PostPosted: Thu Nov 26, 2009 5:55 pm 
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There is a online video by Westex I believe that can show how a arc can in rare cases may travel to other locations. JPEG, this may not help with this question but it is wild to watch and came to my mind when reading your earlier response. Search Westex videos online. There are ten short clips and I cannot remember the number but viewing you will see it.


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PostPosted: Wed Dec 02, 2009 11:09 pm 

Joined: Sat May 30, 2009 6:21 pm
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JPEG wrote:
That's something I'd like to know more about.

Is there any litterature about that or is this simply one more way to be conservative?

Any test or known events?


even if it's not the case you still have access to the level 4 area since every thing is open

what would you mark those area if they were empty and you would only have acces the the incoming side ??


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