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 Post subject: Open Door/Closed Door
PostPosted: Fri Oct 09, 2009 10:29 am 
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There has been some discussion on the Open Door versus Closed Door applicability of the Arc Flash Protection Boundaries (AFB) but I would like to open a topic to specifically discuss this.

There are some on the forum that contend that open door and closed door operations are the same, e.g. the AFB and IE values calculated by hand or by the computer apply whether the door is open or closed. Others contend that the 70E code applies to an open door, exposed energized bus only. This is clearly the intent of the Shock Hazard Boundaries, but less so on the AFB.

It is my understanding that at the last round of updates by the 70E group, this was a topic of much discussion and that the final decision was to make the policies apply to open door operations only. A review of Appendix D in 70E shows the calculations are made based on open air or in an open box, but none are provided for a closed box application and they don’t cite specific data for calculating the AFB nor IE for a closed box scenario. Given that the closed box situation is so variable, I can understand the difficulty in providing a calculation for this scenario. However, most of us would agree that a door on a ‘box’ does provide some protective benefit in an arc flash event even if it is blown off the hinges.

My question is how others view the open/closed door issue and what was the intent of the committee in the last round of updates.

TxEngr


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PostPosted: Fri Oct 09, 2009 6:15 pm 
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There's a note (can't remember in which article, might be before the main task table or in the definition of arc flash hazard in article 90) saying that a closed door doesn't offer any notable protection from an arc flash, unless the gear is arc rated.


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PostPosted: Sat Oct 10, 2009 5:58 am 
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TxEngr wrote:
There has been some discussion on the Open Door versus Closed Door applicability of the Arc Flash Protection Boundaries (AFB) but I would like to open a topic to specifically discuss this.

There are some on the forum that contend that open door and closed door operations are the same, e.g. the AFB and IE values calculated by hand or by the computer apply whether the door is open or closed. Others contend that the 70E code applies to an open door, exposed energized bus only. This is clearly the intent of the Shock Hazard Boundaries, but less so on the AFB.

It is my understanding that at the last round of updates by the 70E group, this was a topic of much discussion and that the final decision was to make the policies apply to open door operations only. A review of Appendix D in 70E shows the calculations are made based on open air or in an open box, but none are provided for a closed box application and they don’t cite specific data for calculating the AFB nor IE for a closed box scenario. Given that the closed box situation is so variable, I can understand the difficulty in providing a calculation for this scenario. However, most of us would agree that a door on a ‘box’ does provide some protective benefit in an arc flash event even if it is blown off the hinges.

My question is how others view the open/closed door issue and what was the intent of the committee in the last round of updates.

TxEngr


I think the 70E is clear on this, the 2009 version ended this debate.

Also there is a debate on what happens with a failed closed door, some data may suggest that this can actually make it worse, by allowing the pressure to build up before the door fails, like pinching a hose then letting go.

The fact is there is no way to calculate closed door senarios, and I dont see how there ever will be, with all the different switchgear designs out there and thee being no way to know the condition of the switchgear. Missing panel cover screws (Or loose), vents, corrosion, etc... Too many variables.


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PostPosted: Mon Oct 12, 2009 7:20 am 
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I disagree with Zog that the 2009 70E put an end to the discussion. Yes there is a FPN that talks about open door/closed door, but as we all know, FPNs are only suggestions and not considered "enforcable" in the code whether it be 70E or 70. The FPN was an acknowledgement that the committee had a difference of opinion on the issue and could not reach a concensus on the question.

Is there anyone who serves on the committee that can comment on this and what the intent of the committee was? Multiple viewpoints would be appreciated.

TxEngr


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PostPosted: Mon Oct 12, 2009 8:47 am 
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I still fail to comprehend how any of the calcs and assumptions that have gone into the standards can be extrapolated to the energy that might be available to cause an arc flash injury after having blown a door open or off of a switchgear cubicle. If it is HRC 3 with the door open, how in the world do we know what it is with the door closed?

Let's put a calorimeter in front of the door first and see what it can measure!

IMHO I believe that there is no correlation to date, and no method to correlate, the IE someone would be subjected to at that point. This issue gets discussed alot as if we actually have data to support an argument. Please show me or point me to the data.

The event doesn't always blow the door off and many times does no damage to it. If it does, how much arc energy or plasma is left? Don't think we know for sure.

Who did the tests or calcs? Lee, IEEE, PG&E, or the 70E folks?


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PostPosted: Mon Oct 12, 2009 11:00 am 
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TxEngr wrote:
I disagree with Zog that the 2009 70E put an end to the discussion. Yes there is a FPN that talks about open door/closed door, but as we all know, FPNs are only suggestions and not considered "enforcable" in the code whether it be 70E or 70. The FPN was an acknowledgement that the committee had a difference of opinion on the issue and could not reach a concensus on the question.

Is there anyone who serves on the committee that can comment on this and what the intent of the committee was? Multiple viewpoints would be appreciated.

TxEngr


OK, lets look at racking operations, HRC 4 for doors open or closed. But you are saying if you do the calculations instead of using the tables you would assume the door would contain the arc flash and not require PPE?? Is this what you are saying or am I reading this wrong?

Until the recent "arc rated" switchgear standard came along the was never any testing or designs doen for arc flash containment. The equipment was never designed to contain an arc flash, so it is silly to assume it would.


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PostPosted: Mon Oct 12, 2009 12:04 pm 
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I am trying to get to what are the actual requirements of NFPA 70E as a consensus standard. Where 70E clearly states that the shock hazard boundaries are for exposed energized bus only, the arc flash boundary is not nearly so clear. Clearly the safest method is to assume that both conditions have the same incident energy and you wear PPE for that energy. Similarly, you are better protected from a car crash if the air bags are constantly deployed whenever you are in the car. This may make driving less comfortable and more difficult but it is certainly safer. The key point is that it isn’t required.

What I’m trying to get to is the intent of the committee in the 2009 version as to whether the standard for the arc flash boundary applies to equipment with the door closed and properly latched. As I stated earlier, it is my understanding that the FPN was included due to a difference of opinion between the committee members as to the application of the standard to closed door systems. Since a consensus could not be reached, the FPN was included but it was not codified in the standard.


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PostPosted: Mon Oct 12, 2009 1:20 pm 
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I don't really have an answer, but would like to contribute a little bit...

My supervisor is on the 70E technical committee, but I don't know if he was present for this discussion. That said, he has maintained that all calculations should be valid with the door open or closed at our site. There is no differentiation.

We had a event a few weeks ago. Electricians were working in a control compartment when a fuse blew, and almost immediately afterward the breaker next to them blew. No one was injured. The breaker compartment had the door closed, and the calculated arc energy was nearly 50 cal/cm2 at 24". Although the door stayed shut, the electricians did report seeing fire shoot out from around the door for a distance of 12" - 18". (As they were moving rapidly in the other direction...!) From the damage that was caused, I don't think that they got the full 50 cal effect. If so, they probably could have been burned even working in the other compartment. This was also on some older switchgear, and the door was very strong and well latched.


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PostPosted: Mon Oct 12, 2009 1:42 pm 
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Closed doors, good solidly built ABB metal clad gear.


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PostPosted: Mon Oct 12, 2009 1:44 pm 
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Closed door, 13.8kV switch, only HRC 2 per the tables with doors closed.

I can do this all day, I see this stuff everyday. I don;t care who intreprets what how, or if a FPN is enforceable or not, unless it is arc rated, switchgear can not be relied on to contain an arc flash.


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PostPosted: Mon Oct 12, 2009 2:06 pm 
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Zog,

I have personal experience with exploding switchgear: both arc resistant and non-arc resistant. Sometimes the doors blow off, sometimes the bolts are stretched and the doors stay on, sometimes whole sections of the gear are just melted away in unexpected places. It's totally unpredictable. The arc resistant stuff is much better in handling the flash but there's still a flash and the energy still goes somewhere. What is safest is not the issue I'm trying to understand.

I'm trying to determine what are the rules as prescribed in the 70E document and by the committee. We can always choose to go beyond the requirements. But many times it has been said that the rules apply closed door as if it were a requirement of the code and I'm not so sure that's the case. That's what I'm trying to get to.


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PostPosted: Mon Oct 12, 2009 2:23 pm 
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Zog wrote:
OK, lets look at racking operations, HRC 4 for doors open or closed. But you are saying if you do the calculations instead of using the tables you would assume the door would contain the arc flash and not require PPE?? Is this what you are saying or am I reading this wrong?

Until the recent "arc rated" switchgear standard came along the was never any testing or designs doen for arc flash containment. The equipment was never designed to contain an arc flash, so it is silly to assume it would.


No that is not what I am saying.....I am simply saying who can know that it is HRC 4 with the doors closed and what calculation/test data did they use. We can calculate what is inside the cabinet but not what might escape. How about HRC4 with doors open, HRC2 with doors closed. And yes I got my data from the same place they must have gotten theirs. Saying it is one thing, proving it is another though. Just because the standard says it doesn't mean they can tell us where they got their data to list it as such.

My common sense tells me that if there is to be an event I would rather have the doors closed. Then I must ask, why do I believe that, because I know some, most, or all of the event will be contained behind the door.

Sort of like they got the 600 volt data?


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PostPosted: Mon Oct 12, 2009 2:44 pm 
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Zog wrote:
Closed doors, good solidly built ABB metal clad gear.


I was sure you could post them all day!....and knew I would get them. :D

But what I want to know is the IE level on the outside of the cabinet and how you would do the calcs. On the one with the cover blown off, was anyone burned or was their head knocked off?

As with WDeanN, I have seen the fire (while I was also movin on), as well as, the results of the events, but we all know many entire flashes are contained by the enclosure. Who takes pictures of them?

I just think it is time for someone to support how an HRC 4 enclosed bus can be determined to be a 4 outside the unit, with doors closed and latched. This has been a major source of heartburn for me since the beginning....or could you already tell. :)

Thanks


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PostPosted: Mon Oct 12, 2009 8:41 pm 
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acobb wrote:
But what I want to know is the IE level on the outside of the cabinet and how you would do the calcs.


You cant, thats my point. If calcs existed they would have to factor in so many things about the design and condition of the enclosure that it would make the fault current calculation seem like 1+2.


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PostPosted: Mon Oct 12, 2009 8:47 pm 
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acobb wrote:
No that is not what I am saying.....


I was quoting TxEng in this post.

acobb wrote:
I am simply saying who can know that it is HRC 4 with the doors closed and what calculation/test data did they use. We can calculate what is inside the cabinet but not what might escape. How about HRC4 with doors open, HRC2 with doors closed. And yes I got my data from the same place they must have gotten theirs. Saying it is one thing, proving it is another though. Just because the standard says it doesn't mean they can tell us where they got their data to list it as such.


As I understand there was a lot of "best guess" from experiences of the commitee members in determining these hazard levels, not so much on data. But, that experience says a lot to me if you look at the backgrounds of the commitee members. Lots of OEM guys there, they should know if the gear will fail better than anyone I would think.

acobb wrote:
My common sense tells me that if there is to be an event I would rather have the doors closed?


I would rather be in the other room myself, only way to be sure.


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PostPosted: Tue Oct 13, 2009 6:02 am 
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If you don’t take into account some credit for the enclosure (arc rated or not) then how are you allowing passage through switchgear rooms, substations, and near normally energized equipment on a daily basis? I don’t think you can expect everyone walking by a switchgear lineup to be in a 40cal suit even that’s the hazard level per the calculation. Nor can you expect to maintain a +30’ FPB when there’s no maintenance activities going on. In many heavy industrial settings switchgear, MCCs, etc can be found everywhere including many control rooms and near operator stations. Should you require a board operator to dawn AF PPE to simply be in the same room with energized equipment? We’ve even found distribution panels, within an office setting, that would require AF PPE (per the calculation) to be near them if you did not take the cover into account.


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PostPosted: Tue Oct 13, 2009 6:03 am 
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A lot of good discussion on this one. The biggest problem I see with this is where do you draw the line. I agree, larger equipment / switchgear etc. may not fail very often, but if it does, doors have been known to blow off at 600 miles / hour. At that point, forget about incident energy, the door will be the problem. The word "duck" comes to mind.

Defining a lower limit of applicibility was not done very well in 70E. Does this apply down to 20A lighting breakers? No one seems to know. I brought this up with a 70E person about a year ago and he seemed to agree, it had no lower boundaries, which could be a problem.

No answer but I believe larger equipment with higher incident energy is a problem and smaller equipment with lower i.e. may not be such a problem. The question (I don't have an answer) is where do you draw the line?

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PostPosted: Tue Oct 13, 2009 10:05 am 
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I may be stirring up a nest. But an opinion is like an ?? ** everyone has one.
The problem for me is I understand both sides of the issue and the only way I can look at it objectively is consider the risk with a combination of components to make a logical conclusion.

Is this a policy or company plan/training issue? Maybe one company writes that due to the equipment high IE no one is allowed in the switchgear room without CAT 4 PPE and locks the door only with access by EWP. Maybe another company says, Work only on the switchgear when de-energized. Another says enter only with a EWP and so on.

Again I would think that it a task related issue to some degree. Does the company commonly rack in live devices? Do people pass by this equipment regularly? Is the equipment condition deteriorating?

In my opinion we could argue about the severity of risk door open or closed but the real world still exist. Companies have to be informed of the hazard and create a plan to deal with it. If not then they are in trouble if something happens and they knowingly allowed the hazard to exist.

Again just my opinion, determine the risk and IE, training workers of risk, training to minimize the risk, and a plan on what to do with certain task all documented and all levels of management agreeing.

Easy on me now just an opinion.


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PostPosted: Tue Oct 13, 2009 10:18 am 
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SCGEng1 wrote:
If you don’t take into account some credit for the enclosure (arc rated or not) then how are you allowing passage through switchgear rooms, substations, and near normally energized equipment on a daily basis? I don’t think you can expect everyone walking by a switchgear lineup to be in a 40cal suit even that’s the hazard level per the calculation. Nor can you expect to maintain a +30’ FPB when there’s no maintenance activities going on. In many heavy industrial settings switchgear, MCCs, etc can be found everywhere including many control rooms and near operator stations. Should you require a board operator to dawn AF PPE to simply be in the same room with energized equipment? We’ve even found distribution panels, within an office setting, that would require AF PPE (per the calculation) to be near them if you did not take the cover into account.

I don't think this scenario is much of a problem. FPN No. 1 to the 70E Article 100 definition of Arc Flash Hazard makes it clear that some interaction with the equipment is needed for an arc hazard to exist per NFPA 70E.

The problem is in defining what interaction constitutes a hazard. If a 480 V MCC has a calculated IE of 5 cal/cm², do you need PPE category 2* to turn a motor off?

I would contend that if the HRC of an activity in Table 130.7(C)(9) is zero, then FPN No. 2 in the Arc Flash Hazard definition implies that the activity is not one that poses an arc hazard. But this is certainly open to other interpretations.

Fine print notes (FPN) are expanatory only and not enforceable, and the definition uses the term "possible release of energy." Since it is possible for an arc to occur in a distribution panelboard while you're just walking by, you could interpret this to mean that an arc flash hazard exists, but I don't think that is the intent.


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PostPosted: Tue Oct 13, 2009 11:52 am 
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TCG - I agree with much of what you say. But in order to make those decisions you must have a base or starting point. That starting point is ‘what does the 70E Standard say’ as well as what was the intent of the committee.

Once you know the starting point, then you can make those decisions of how you’re going to implement everything and the rules you’re going to create. Many of the rules at my facility are more stringent than the requirements of 70E and I suspect many others do the same. But you still have to know what that minimum requirement is.

There have been statements by some that the closed door operations are considered the same as open door operations in the 2009 70E Standard. That is not clear to me and as I have stated earlier my understanding is that this was not the intent of the committee.

I don’t believe that it was not the intent of the committee to make things overly complicated but was to create a workable solution that provides a safe workplace for employees. The issue we now struggle with is in trying to understand what this group really meant.


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