Arc Flash Study

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moosewl

Member
We are in the process of doing an arc flash study for our facility. I think the Sr. Engineering who is doing the calculations is a bit confused and I need some direction on how to help him.

He is calculating the arc flash based on various working distances depending on the task to be performed. Example, racking a 480V feeder breaker in a substaion has a working distance of 24". If performing voltage testing on the breaker to verify that the 480V power has been removed the working distance is 18". He then wants to create a label for each task and place it on the equipment.

Is this the correct way to do this study?
 

nollij

Member
Location
Washington
We are in the process of doing an arc flash study for our facility. I think the Sr. Engineering who is doing the calculations is a bit confused and I need some direction on how to help him.

He is calculating the arc flash based on various working distances depending on the task to be performed. Example, racking a 480V feeder breaker in a substaion has a working distance of 24". If performing voltage testing on the breaker to verify that the 480V power has been removed the working distance is 18". He then wants to create a label for each task and place it on the equipment.

Is this the correct way to do this study?

The working distance is taken to mean the distance that the chest and face are away from the energized equipment while working.

There is a lot of leeway in Arc Flash studies as there is nothing/no one auditing how these variables are arrived at. The goal of an Arc Flash study is to as accurately as possible represent the system and identify the risks to the employees. In this case, using the two working distances may be valid for the tasks at hand.

However, having two stickers on the gear with seperate working distances may not be apparent to those working on the equipment what the difference is. It could be a training nightmare and cause confusion. The electricians would need to know that the difference between the two stickers refers to working distances and these working distances correspond to the activities being performed.

I would recommend using the closest possible working distance that tasks will be performed at the gear as your working distance. Zero confusion, the employees only have to manage one set of PPE for that gear, etc.
 

zog

Senior Member
Location
Charlotte, NC
We are in the process of doing an arc flash study for our facility. I think the Sr. Engineering who is doing the calculations is a bit confused and I need some direction on how to help him.

He is calculating the arc flash based on various working distances depending on the task to be performed. Example, racking a 480V feeder breaker in a substaion has a working distance of 24". If performing voltage testing on the breaker to verify that the 480V power has been removed the working distance is 18". He then wants to create a label for each task and place it on the equipment.

Is this the correct way to do this study?

He needs to forget about tasks and pick one working distance to use for his calculation. Way too confusing (as nollj pointed out).
 

skeshesh

Senior Member
Location
Los Angeles, Ca
I've been involved in multiple arc flash studies and never seen multiple labels for the same equipment. The worst case is always posted. You may need to look for a more experienced or specialized consultant next time around.
 

zog

Senior Member
Location
Charlotte, NC
I've been involved in multiple arc flash studies and never seen multiple labels for the same equipment. The worst case is always posted. You may need to look for a more experienced or specialized consultant next time around.

Nearly every time I have seen the study done in house they have regretted it by the end. But there are also many self knighted "experts" out there doing these, so be sure to to your homework.
 

skeshesh

Senior Member
Location
Los Angeles, Ca
Nearly every time I have seen the study done in house they have regretted it by the end. But there are also many self knighted "experts" out there doing these, so be sure to to your homework.

Very true. There's no real "credentials" as far as licensing for arc flash. The person I'm thinking about is someone I know personally - when he bids for a job (though many time he's contacted by repeat customers or word of mouth) he includes credentials such as letters of recognition from several large clients including GE and Siemens as well as a list of over 50 sizable projects. I guess what I'm getting at is when hiring someone it's a good practice to ask for recommendations and a list of previous projects; both should be easy to provide if the person is experienced.
 
I've been involved in multiple arc flash studies and never seen multiple labels for the same equipment. The worst case is always posted. You may need to look for a more experienced or specialized consultant next time around.

I strongly disagree with that statement. There are several situations, with more emerging where multiple labels are appropriate. Switchgear applications are the most obvious, where the incoming line conductors are not safe with any PPE, but the feeder sections have a lower hazard level.

Six inches of differentiation doesn't seem enforceable, but there are other conditions that are, such as a maintenance short-time delay override switch which may not be possible to engage for some operations.
 

zog

Senior Member
Location
Charlotte, NC
I strongly disagree with that statement. There are several situations, with more emerging where multiple labels are appropriate. Switchgear applications are the most obvious, where the incoming line conductors are not safe with any PPE, but the feeder sections have a lower hazard level.

Six inches of differentiation doesn't seem enforceable, but there are other conditions that are, such as a maintenance short-time delay override switch which may not be possible to engage for some operations.

Not saying multiple labels are a bad idea, but multiple labels with different assumed working distances is, it will get misinterpreted.

Multiple labels for things like a maintenence or arc flash reduction switch is pretty common, I assume that is what you are talking about, neber heard the term STD override switch, does not sound like a good idea to me. :)
 

moosewl

Member
Thanks for all your inputs. I hope I can convince him that multiple labels with multiple working distances is a bad idea.

I would expect to see, on a 480V substation, multiple lables but with the same working distance. I would expect a label on the main/incoming breaker, and a label for operating the feeder breakers. But with the path we are on, I think we could end up with possibly 4 or more labels on a single substation.

One of the reasons we are doing this study is to reduce the number of calls from our maintenence department asking about proper PPE. I think the number of calls will increase with this many labels.
 
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