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 Post subject: Equipment Labels - Do you know what they mean?
PostPosted: Fri Aug 19, 2011 9:39 am 
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I know this has been discussed over and over but I wanted to put the questions out there again to spark some debate. When a study is complete and the equipment is labeled do you believe the labeled incident energy value applies for all situations, all tasks, all the time?

What about the flash boundary? Again all situations all the time? If so, how do you handle normal foot traffic or other unrelated activities near the equipment (assuming you are within the labeled boundary)? In my opinion, a procedure or a look up table is one thing but actual labels on the equipment tend to make a lot of people ask very specific questions.


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PostPosted: Fri Aug 19, 2011 12:11 pm 
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The intent is the calculated incident energy applies when an arc flash hazard exists. This could include "interaction" or when there are exposed energized parts.

If the equipment has the door closed and there is no interaction, i.e. normal conditions, then there should be no hazard. (unless the equipment suddenly decides to blow up from an overdutied device opening too large of a fault current but we won't go there with this thread :) )

The arc flash boundary (the word "protection" is being deleted in 2012) applies for the same situation as above. If it applied all the time that would create quite a bit of trouble for situations such as walking down a hospital corridor with panels along the wall.

I am sure there are other great opinions with the forum gang as well. Maybe some others have different views.

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PostPosted: Fri Aug 19, 2011 12:36 pm 
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I believe that once you have identified the level of the hazard you have in a way locked your self into that incident energy for all tasks (Interactions) unless the equipment is liasted as arc rated.

It does not (IMO) apply to people just walking by, however, some equipment such as MCC's that operate without interaction could present a liability problem. In fact a guy I know who works for a testing company was burned from an arc flash that occured in a MCC as he was just walking past it on his way back from lunch.


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PostPosted: Fri Aug 19, 2011 3:12 pm 
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Yes it’s the “This could include interaction…” and “…when an arc flash hazard exists“ talk that seems to always cause the problems.

These issues seem to be answered based on opinions. One would think a label would put all discussion to rest. I guess it can and does for some but maybe not so much for others. From what I’ve seen over the years it typically invites more pointed questions.


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PostPosted: Wed Aug 24, 2011 8:46 am 
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I was expecting more opinions and discussion on this topic…maybe not. Let me try it this another way. If your job is to conduct studies and present the results to a customer how do you explain the equipment labels if they ask , “now when do the numbers apply?” :confused:

I suppose the conservative answer, as Zog noted, is for all tasks and interactions but even this line of thinking tends to snow ball out of control leading to more questions.

As an example…What about automated or remotely operated equipment? This type of operation is very common in the industrial world now days with computers actually running the process. It is very common for motors to start and stop with little to no local interaction. Zog even noted an example of an MCC flash while walking by.

One could argue an operator at terminal or a control system, starting or stopping a motor remotely is in fact interacting with the equipment. While this action would not directly impact the operator himself it could impact anyone close to the equipment being remotely operated. So do you require everyone entering an MCC room to dress to the maximum level? Do you disable the automatic control system when entering the room? The answer is probably no to both but these are real world questions that do not have clearly defined answers or requirement.

If you consider the example above, and take no credit for the equipment doors or other factors then it can become hard to explain how simply walking by, sweeping the floor, or any other task that puts an employee close to automated equipment is any different than operating it locally, as designed, with the door closed.


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PostPosted: Wed Aug 24, 2011 2:34 pm 
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SCGEng1 wrote:
... tends to snow ball out of control leading to more questions.

As an example…What about automated or remotely operated equipment?


I can see it getting even worse. What if you are walking by a typical panel, there is a short circuit, the breaker has an inadequate interrupting rating, there is a failure, it escallates into an arc flash etc.

This is probably a pretty remote possiblity but I believe it is possible. :eek: Would this mean we need to prohibit office people from walking by panels too?

I see your point SCGEng. My understanding is the calculations indicates the energy that could be there and does not address how it happened. Answering the "how it could happen question" would (has?) open up quite a can of worms.


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PostPosted: Wed Aug 24, 2011 8:12 pm 
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SCGEng1 wrote:
As an example…What about automated or remotely operated equipment? This type of operation is very common in the industrial world now days with computers actually running the process. It is very common for motors to start and stop with little to no local interaction. Zog even noted an example of an MCC flash while walking by.

One could argue an operator at terminal or a control system, starting or stopping a motor remotely is in fact interacting with the equipment. While this action would not directly impact the operator himself it could impact anyone close to the equipment being remotely operated. So do you require everyone entering an MCC room to dress to the maximum level? Do you disable the automatic control system when entering the room? The answer is probably no to both but these are real world questions that do not have clearly defined answers or requirement.


I suppose the proper thing to do is to set up barriers before operating the equipment remotely to prevent anyone from getting any closer to the equipment than the arc flash boundary.


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PostPosted: Thu Aug 25, 2011 8:05 am 
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SCGEng1 wrote:
When a study is complete and the equipment is labeled do you believe the labeled incident energy value applies for all situations, all tasks, all the time?


Again I stress that your serving utility's primary goal is to keep the lights on. It keeps the meter turning, the revenue flowing, and the customers happy. To accomplish this, they will go to great lengths to temporarily reconfigure circuits for maintenance, and your burnt out serving transformer will be replaced with what's in stock. And they may be upgrading facilities just to handle load growth. So the answer is no.


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PostPosted: Tue Aug 30, 2011 8:31 am 

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Any incident energy analysis simply gives us a quantitative way to represent and protect ourselves against an arc flash HAZARD. It does not identify the RISK involved with that hazard. The NFPA 70E attempts to take risk into account with their hazard risk tables, but anyone doing calculations knows that we are not able to mix the NFPA tables with the incident energy analysis. However, we actually are doing a risk analysis every time we do a calculation: we are assuming that any time someone is 'interacting' with electrical equipment, there is an equal risk (100%) that an arc flash will occur, and that the worker will be exposed to the maximum incident energy, regardless of HOW they are interacting with it (eg. closed door disconnect operation vs. exposed bus interaction).
However, when someone is just walking past a panel, they are not exposed in the same manner (already moving, side is exposed instead of chest, greater distance, doors COULD increase protection.... ;) ), and the risk is much lower. In fact, this particular risk can almost be quantified: Avg. walking speed = 5 km/h, Example MCC bucket width = .001016 km (40 inches), Exposure time = 0.73152 s. (I apologize about the distances....My Canadian is showing :D ).
The overall goal of the NFPA 70E and the incident energy calculations is to prevent loss of life. Based on the sample calculation above, it almost has to be a perfect set of events for someone to be walking by a panel and be exposed to the same level of hazard that an electrician standing directly in front of it, interacting with it, is exposed to. Therefore the RISK associated with the hazard is much less, as well as the exposure to the individual. I believe this is the intent of the IEEE-1584 2 second rule as well. The hazard is still there, but the exposure to the person is gone (or minimized), as they have removed themselves from the hazard after 2 seconds.
Unfortunately, these type of risk analyses are ultimately going to rely on somebody's judgement, whether it be the consultant doing the analysis or the company making the Safe Work Procedure. If the company decides to make everyone wear PPE when walking past the equipment because it COULD be operated remotely (automatically or manually), they have assessed the risk and believe that it is the same as if they are standing directly in front of the panel interacting with it.
As far as manual remote operation goes, it would be good practice to check the AFB area of the affected equipment before operation if it poses a significant hazard (>1.2cal/cm2).
Zog - I'd be interested to hear some of the details of your friend that was walking past the panel. Was he injured? What were the extent of the injuries compared to the calculated incident energy? What caused the arc flash?


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PostPosted: Wed Aug 31, 2011 8:38 am 

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m cmbl, I like your thinking. It does seem like risk has nothing to do with IEEE calculations. My guess (and it is only a guess) is that no one wants to stick their neck out and factor in risk to reduce the level of PPE (even though NFPA does with HRC) because of the possible legal ramifications.

So if there is a one in a billion chance, focus on the hazard not the one in a billion possiblity of it occuring. ...unless I missed something?


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PostPosted: Wed Aug 31, 2011 11:15 am 

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S. Patel wrote:
My guess (and it is only a guess) is that no one wants to stick their neck out and factor in risk to reduce the level of PPE (even though NFPA does with HRC) because of the possible legal ramifications.

You are absolutely right. The legal ramifications are paramount, but I think that there is a case for 'Due Dilligence' if you can back up your Risk Assessment with some sort of reasonable justification. Obviously the best kind of justification would be quantitative, but there are very few risks that can actually be quantified. The comment that I wrote above was more to give my best guess at clarifying some of the rules that we are already using when we do calculations. The initial question was regarding walking past or working around electrical equipment. If it is a 25 cal/cm2 hazard, that hazard exists regardless of whether the person is interacting or not, but the risk of an arc flash happening to well maintained equipment is low, and the risk of exposure to the person present is even lower, based on some of the variables that I listed in the previous comment.
Essentially, the same is true about Arc Resistant Switchgear. When we do the calculations, the Arcing Current and associated incident energy are still the same at the switchgear, but the risk of arc flash exposure when operating switches with the door closed (and properly latched) has been greatly reduced because of the venting and re-enforced doors.
If you saw my thread regarding the IEEE-1584 Excluding Mains on QMB panels, I was fishing for information to try to quantify the risk of operating a <1.2 cal/cm2 (including main) 30A disconnect downstream of the main. I believe there is a very low risk of a <1.2cal/cm2 plasma cloud bridging the main fuses before they are able to clear the fault, but have yet to find any proof, let alone anything that could be considered 'reasonable justification'!

S. Patel wrote:
So if there is a one in a billion chance, focus on the hazard not the one in a billion possiblity of it occuring

I believe that is what the initial question by SCGEng1 was trying to address. There is always a hazard, and there is probably close to a one in a billion possibilty that a panel will flash at the exact moment that someone walks past it and experiences the full incident energy associated with it, but we still aren't requiring people to wear 40 cal/cm2 suits just to walk past it. So in this case, we are focusing on the odds, not the hazard.


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PostPosted: Wed Aug 31, 2011 3:17 pm 
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Doesn't 110.7(F) require risk to be considered?


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