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 Post subject: Exposed or Not Exposed, That's the ?
PostPosted: Thu Jan 28, 2010 7:49 am 
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Relatively new to forum, not new to Arc-Flash.
Question:
I have the following equipment: 3 phase, low voltage AC (but above 240V), busbars... similar to crane rail... each busbar/conductor is individually protected with an insulating cover that covers the entire conductor except for the face where the collectors contact the rail for power.

In an arc-flash analysis, would you consider this exposed equipment????

This is a real application that I have been struggling with for quite a while.

Definition of exposed in IEEE 1584: Capable of being inadvertently touched or approached nearer than a safe distance by a person. It is applied to parts that are not suitably guarded, isolated, or insulated.

Also, one must consider definition of "working on or near"... say, if a worker is simply walking by this type of busbar arrangement, within the calculated FPB, are they "working on or near" exposed equipment?


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PostPosted: Thu Jan 28, 2010 9:33 am 
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JLY wrote:
Relatively new to forum, not new to Arc-Flash.
Question:
I have the following equipment: 3 phase, low voltage AC (but above 240V), busbars... similar to crane rail... each busbar/conductor is individually protected with an insulating cover that covers the entire conductor except for the face where the collectors contact the rail for power.

In an arc-flash analysis, would you consider this exposed equipment????

This is a real application that I have been struggling with for quite a while.

Definition of exposed in IEEE 1584: Capable of being inadvertently touched or approached nearer than a safe distance by a person. It is applied to parts that are not suitably guarded, isolated, or insulated.


For arc flash, it does not matter if it exposed or not.

JLY wrote:
Also, one must consider definition of "working on or near"... say, if a worker is simply walking by this type of busbar arrangement, within the calculated FPB, are they "working on or near" exposed equipment?


Only if they are interacting with the equipment.


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PostPosted: Thu Jan 28, 2010 12:29 pm 
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I guess I'm not sure I agree.
I know that you've got tons of experience with reading and interpreting NFPA 70E.
However, how do you explain the fact that in Table 130.7(C)(9), below 1kV, all HRCs for actions with enclosure doors closed are HRC 0, while actions with doors open (even just opening the door), are some higher level of HRC?
I know, I know, racking being the exception.

Also, following your logic, you can open a switchgear cubicle door, with the proper AF PPE on of course, then end your "interaction" with the switchgear, and remove your AF PPE?

Not trying to be a smart-alec, just trying to understand your answer.

Exposed = arc flash hazard may exist
Enclosed + provided a person is interacting with the equipment + improperly installed and maintained = arc flash hazard may exist

This is why I was trying to get people's interpretations of my application with regards to "exposed."


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PostPosted: Thu Jan 28, 2010 1:17 pm 
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JLY wrote:
Exposed = arc flash hazard may exist
Enclosed + provided a person is interacting with the equipment + improperly installed and maintained = arc flash hazard may exist

This is why I was trying to get people's interpretations of my application with regards to "exposed."


Unless your enclosure is arc rated then yes that is correct. There have been some very in depth discussions on this topic, use the search feature to find them. But the premise is that enclosures were never designed to contains an arc flash and the manufactures make no clains that it will. I have posted many photos on this forum (As have others) of enclosures failing from an arc flash event.

Now the arguement here is the level of equipment where this is a concern. Switchgear, consensus is yes. Light switch, consensus is no. Where is that line? No one seems to know. Keep in mind that HRC=O does not mean there is not a flash hazard.


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PostPosted: Thu Jan 28, 2010 2:40 pm 
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So, back to question...

So back to my original question...

3 phase, low voltage AC (but above 240V), busbars... similar to crane rail... each busbar/conductor is individually protected with an insulating cover that covers the entire conductor except for the face of the conductor where the collectors contact the rail for power.

In an arc-flash analysis, would you consider this exposed equipment????


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PostPosted: Fri Jan 29, 2010 6:51 am 
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I would, other veiws may vary.


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PostPosted: Fri Jan 29, 2010 7:56 am 
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Exposed or not?

Is the system solidly grounded?
What is the position of the rail - is it up in the ceiling or can it be touched from normal working position?
How large is the opening in the bus bar insulation?
What type of protective device is in use?

Does it actually meet the requirements of IEEE 1584 - +125 KVA??


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PostPosted: Fri Jan 29, 2010 10:31 am 
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Exposed Energized Parts and the Arc Flash Boundary

This is an interesting one. The NFPA 70E standard 2009 defines "exposed energized conductors or circuit parts" which you cited BUT it also defines "arc flash hazard" with Zog alluded to.

In that definition it says, "FPN No. 1: An arc flash hazard may exist when energized electrical conductors or circuit parts are exposed or when
they are within equipment in a guarded or enclosed condition, provided a person is interacting with the equipment in
such a manner that could cause an electric arc. Under normal
operating conditions, enclosed energized equipment
that has been properly installed and maintained is not likely
to pose an arc flash hazard."

This requires engineering judgment. Exposed does not mean a hazard exists. It MAY EXIST. Guarded and Insulated are interesting words which have to be thought about. If it is 15 ft off the ground, it could be considered guarded and insultated in many conditions but the AHJ (Authority Having Jurisdiction) has to make that call with solid engineering judgment.

I would say if this is a raised buss and no work is going on that the area is guarded you are probably NOT in an arc flash hazard walking through the plant; as long as you are not crossing the limited approach boundary for the voltage. Say a crane or elevated buss. This is common in plants and unless live work is occurring on the crane or some one is walking even with the busbar up on the second floor and throws a wrench etc they are unlikely to get an arc flash. NFPA 70E members are NOT trying to keep work from occurring. They are trying to get you to think through a job to make sure you don't have undue exposure. I can't give an opinion without more full knowledge but the quote above should be helpful.


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PostPosted: Fri Jan 29, 2010 10:49 am 
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High-Resistance Grounded
Can't be touched from normal working position, not elevated, basically mounted on the floor, but with a gap in the floor between the worker and the exposed bus.
Opening is 7/8".
Power Circuit Breaker with Trip Unit... LSI...
Above 125 kVA...


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PostPosted: Fri Jan 29, 2010 10:54 am 
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My engineering judgement has been the following:
Considered exposed.
Workers within the flash protection boundary, but NOT interacting/working with busbars, and NOT working near the busbars, do not require AF PPE, as the equipment has been properly installed and maintained.
So basically, if the worker is simply passing by or walking through the plant, inside FPB, but with no way of actually contacting busbars even accidentally due to gap in floor, and not remaining stationary in the location to perform some other work, then they do not require more than HRC 0, which is our standard uniform.
Working on or near, inside the FPB, HRC as calculated.
I just wanted to make sure I wasn't being too conservative, and from the looks of the replies, I don't think I am.

By the way thanks to all so far...


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PostPosted: Sat Jan 30, 2010 9:34 am 
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Exposed Energized Parts and the Arc Flash Boundary

Sounds like a reasonable plan. Could look at the possibility of covering with a Lexan guards etc. to prevent arc flashes but I would guess access must be important. One thing with it being "exposed" is no conductive tools can be brought within 42" away.

Just something else to consider.


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PostPosted: Thu Feb 04, 2010 10:21 am 
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I agree that Arc flash may exist in both exposed and not exposed condition. However, the levels should be different. When you do the calculation, it is based on exposed condition mainly. So do you have to wear the same level PPE when you just operate the breaker on door close condition?


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PostPosted: Thu Feb 04, 2010 2:11 pm 
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PPE required

The debate rages on...


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PostPosted: Fri Feb 05, 2010 7:32 am 
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You are right, safety is the primary goal, but make it too conservative is not the goal of arc flash study either. Maybe we need to put two labels on the equipments, one for exposed and one for door closed. Does that sound pratical?


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PostPosted: Fri Feb 05, 2010 7:44 am 
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Canuck01 wrote:
The debate rages on...


And it will......

But, keep this in mind. When we try to weigh "risk", evaluate hazards, calculate probability, we are talking about lives. When you are the one laying there in that burn unit, in the tub of chlorine being debreeded 3 times a day wishing you could die so the pain stops, you don't care what the odds were, you don't care who decided the risk was low enough.

I have been there, holding the hand of someone I love in the burn unit, and can tell everyone, nothing matters at that point.

Sure it stinks to wear the PPE, it is a cost to companies up front but safety is good business, the real costs are from the doctors and lawyers after something happens. Blaming OSHA for companies leaving the country is silly, just a drop in the well. Unions, taxes, bonuses, high wages, poor work ethic (Somehow lost the last generation or two), trades people sitting around playing cards all day, outragous salaries, are all much bigger factors than safety for the loss of manufacturing in the US.


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PostPosted: Sun Feb 07, 2010 9:37 pm 
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I have successfully trained well over a thousand (a guess) maintenance personnel from over 100 companies on the arc flash hazard. You have to be realistic when trying to convert them to our way (the safe way) of working energized. I have no doubt that a large percentage of those now work safer.

If I made a black and white statement that enclosed switchgear was an arc flash hazard I would have lost a large percentage of those that now work safely. I just investigated an arc flash within old switchgear. It calculated out at 63 cal/sq cm and it did a very good job of containing the arc.

I believe it does a major injustice to the industry to profess the belief that enclosed equipment is an arc flash hazard until said equipment has been tested in the same manner as the original IEEE test sequence. I think common sense should prevail. Energized work permits allow us to view the equipment than make a decision of that equipment.

I think most of us have seen the aftermath arc flash incidents. I have investigated over a dozen myself, this does not make every piece of equipemnt a hazard.


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PostPosted: Mon Feb 08, 2010 6:40 am 
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Flash wrote:
I have investigated over a dozen myself, this does not make every piece of equipemnt a hazard.


Every piece of equipment is a hazard in the same way that every car is a hazard.


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PostPosted: Mon Feb 08, 2010 8:18 am 
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Flash wrote:
I have successfully trained well over a thousand (a guess) maintenance personnel from over 100 companies on the arc flash hazard. You have to be realistic when trying to convert them to our way (the safe way) of working energized. I have no doubt that a large percentage of those now work safer.

If I made a black and white statement that enclosed switchgear was an arc flash hazard I would have lost a large percentage of those that now work safely. I just investigated an arc flash within old switchgear. It calculated out at 63 cal/sq cm and it did a very good job of containing the arc.

I believe it does a major injustice to the industry to profess the belief that enclosed equipment is an arc flash hazard until said equipment has been tested in the same manner as the original IEEE test sequence. I think common sense should prevail. Energized work permits allow us to view the equipment than make a decision of that equipment.

I think most of us have seen the aftermath arc flash incidents. I have investigated over a dozen myself, this does not make every piece of equipemnt a hazard.


So you have trained thousands of people that enclosed switchgear is not an arc flash hazard? Even though non arc rated switchgear was never designed or tested for containing an arc flash?


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PostPosted: Tue Feb 09, 2010 1:17 pm 
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It goes to another extreme. I think that we should consider of putting two labels on equipments. The enclosure does provide some sort of mitigation, but can't eliminate arc completely. Let's compare the safety condition between a driver in the car and a motorcycle driver, don't you think the one inside the car is safer?


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PostPosted: Tue Feb 09, 2010 1:53 pm 
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Door closed or open?

Without testing, nobody can assume the arc flash will be any less severe for closed doors. Many types of switchgear doors are fastened with screws or other flimsy fasteners that would not stand up to any blast. I'm struggling with the locking out scenario right now, and my site PPE exceeds 8 cal (minus the faceguard). Do I follow the posted IE or will I assume the act of locking out is inherently safe...
I'm slowly falling to the side of following the posted IE however difficult. Long term I plan to engineer out the hazard. Short term will be to operate the higher IE disconnects remotely or isolate upstream.
Keeping the IE below my standard issue PPE rating and proper training may be the answer for me.


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