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 Post subject: "Exposed Live Parts"
PostPosted: Thu Oct 14, 2010 8:14 am 
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Joined: Thu Oct 14, 2010 8:04 am
Posts: 11
Hello All, a thanks for the help in advance.

I'm am preforming my first short circuit, protective coordination and arc flash hazard report for my company. Obviously i've had many questions thus far and seemed to answer most.

My question refers to Arc Flash Boundry and the actualy implications of it. From what i have gathered thus far, codes seem to be rather...contradicting in many cases.

So...when Arc Flash Boundry and incident energy levels have been calculated (w/ easypower software), how are these applied? Basically, I have a 480V walk in double ended enclosure calculated to be a level #3 and AFB of 110". The enclosure only gives NEC working space (3' 6"), so do i need a #3 suit to go in and look at a breaker? Do i need it to operate the breaker? Do i need it to open the dead front panel cover and look at the breaker trip settings? Do i need it to rack out the breaker? (i can assume yes here).

My question refers to exposed live parts as well. In NEC, exposed live parts may mean a dead front CB handle, in reference to working space. To me, exposed live parts would be opening the cover and visually seeing busbar. Where is this distinguished?

Often you have balconies with MCCs, and potentially 3 ft of walking space then a rail. For someone to walk across the balcony to get to the other side does he need a suit if crosses a AFB? (assuming all dead front doors closed) Does he need one to open/close a breaker?


I know i asked alot, but i hope i can get good responses. Thanks in advance.

HarcFlash


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PostPosted: Thu Oct 14, 2010 8:40 am 
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Joined: Mon Mar 29, 2010 11:52 am
Posts: 110
Location: Yankton SD/ Lead SD
IMHO, I would respond yes to your first set of questions. Secondly, anytime you interact with electrical equipment you will need to have on your PPE. With the panels on the mezzanines, or in hallways, office type spaces, or any other location you will not need to have PPE to be around them as long as you are not interacting with the equipment. If someone is working on the equipment, then you would have to have your PPE on in order to cross the AFPB.


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PostPosted: Fri Oct 15, 2010 8:12 am 
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Joined: Wed Oct 29, 2008 6:06 am
Posts: 136
Location: Michigan
Service Equipment AF Labels

Under the 2004 edition of 70E I had this figured out; however, in the 2009 edition with the new definition of the Arc Flash Protection Boundary I’ve had to rethink this. The AFPB is now defined as a distance from a perspective arc source whereas before it used to be a distance from exposed live parts. We have decided that wearing PPE to operate the breakers on the services is prudent even with all covers securely in place and no exposed energized parts.

Currently there is only one label on the 2000A service which shows 88.5 cal/cm2. This was calculated (w/ EasyPower) using the ‘Excluding Main’ output and therefore it ignores the service’s main breaker and is instead looking at the utility fuse upstream. Showing only the worst case scenario (line side of main) was desirable since one label reduces the chances of someone reading the wrong label and not wearing the appropriate PPE. Besides, most of the time PPE would only have to be worn to verify de-energization.

However, under the new definition of the AFPB, operating a breaker on the service with all covers securely in place and no exposed energized parts now requires PPE and 88.5cal/cm2 seems really extreme for this task. Calculating the IE using ‘Including Main’ now looks at the service’s main breaker and results in 2.1 cal/cm2 (load side of main) which I feel is a much more reasonable PPE level for this task.

So I am thinking each service now needs two arc flash labels. One would specify PPE to be worn for interaction (other than w/ the main) with covers ON and the other for interaction with covers OFF. Qualified electrical workers would then also be trained on this. Does this sound feasible? How are others addressing this?


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PostPosted: Fri Oct 15, 2010 11:09 am 
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Joined: Wed Jun 04, 2008 9:17 am
Posts: 411
Location: Spartanburg, South Carolina
A King wrote:
Under the 2004 edition of 70E I had this figured out; however, in the 2009 edition with the new definition of the Arc Flash Protection Boundary I’ve had to rethink this. The AFPB is now defined as a distance from a perspective arc source whereas before it used to be a distance from exposed live parts. We have decided that wearing PPE to operate the breakers on the services is prudent even with all covers securely in place and no exposed energized parts.

Currently there is only one label on the 2000A service which shows 88.5 cal/cm2. This was calculated (w/ EasyPower) using the ‘Excluding Main’ output and therefore it ignores the service’s main breaker and is instead looking at the utility fuse upstream. Showing only the worst case scenario (line side of main) was desirable since one label reduces the chances of someone reading the wrong label and not wearing the appropriate PPE. Besides, most of the time PPE would only have to be worn to verify de-energization.

However, under the new definition of the AFPB, operating a breaker on the service with all covers securely in place and no exposed energized parts now requires PPE and 88.5cal/cm2 seems really extreme for this task. Calculating the IE using ‘Including Main’ now looks at the service’s main breaker and results in 2.1 cal/cm2 (load side of main) which I feel is a much more reasonable PPE level for this task.

So I am thinking each service now needs two arc flash labels. One would specify PPE to be worn for interaction (other than w/ the main) with covers ON and the other for interaction with covers OFF. Qualified electrical workers would then also be trained on this. Does this sound feasible? How are others addressing this?


These are my thoughts, and I'm sure others would disagree.

I would have one label for the main, marked "Dangerous - No Safe PPE Level". I'd use a label with an IE of 2.1 cal/cm² for the feeders, without distinguishing between covers on or off.

If you used 88.5 cal/cm² on the feeders, how would you de-energize and test equipment on the feeder? You couldn't trip the feeder breaker because you would need 88.5 cal/cm² PPE. You would have to de-energize the service to work on any equipment fed directly from the main distribution panel.


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PostPosted: Fri Oct 15, 2010 7:42 pm 
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Location: Toronto, ON, Canada
I assume the equipment is a main switchgear, say, a typical 4 section switchgear with internal barrier. You have an option to demarc the two sections of the switchgear clearly, where the barrier is. On one side of the demarcation goes the Dangerous warning label, on the other side goes the 2.1 cal warning label. But I would not do that, it will cause confusion, and in a court of law, the potential victim can claim that he was confused.

I would just put the Dangerous warning label, and if the electricians wanted to work on the feeder equipment on the line side of the main, they shall use extreme caution and energized work permit for 2.1 cal.

If the workers want to operate the main disconnect, they shall use hot sticks with sufficient distance apart, or look into remote operating it,

You could also look into installing some IR windows for the main, for IR maintenance


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