110.16 arc flash label

[zog]

Then how do you calculate a value with the covers on?

John M

You dont, you assume the covers are off, have vents, or will fail for an analysis.

 

[mayanees]

no, what I do..

no, what I do..

No, I've given some thought to this, and what I do, is I calculate the value of the exposed bus incident energy, and post the corresponding PPE requirement. That's what an electrician suits up for if he needs to work on the system when it's energized.
Then I calculate the 'covers on' incident energy buildup on the grounded switchgear metal. ZERO, which translates to a level ZERO PPE requirement...
And then I default to the table for the more restrictive PPE requirement when someone works at the switchgear with the covers on, and I specify that level of PPE.
There's a point where you apply problem-solving engineering skills while working within the regulations, but use common sense in the process.
John M

 

[zog]

Then I calculate the 'covers on' incident energy buildup on the grounded switchgear metal. ZERO, which translates to a level ZERO PPE requirement...

Exactly how do you do that? Never seen any equations for a covers on calc.

And then I default to the table for the more restrictive PPE requirement when someone works at the switchgear with the covers on, and I specify that level of PPE. There's a point where you apply problem-solving engineering skills while working within the regulations, but use common sense in the process.
John M

Again, you cant mix the calcs and the tables and pick which one works better for you. The tables are not based on any formulas or lab tests, they are task based and have many other factors involved. There is a difference between hazard and risk, apples and oranges.

 

[jghrist]

Then I calculate the 'covers on' incident energy buildup on the grounded switchgear metal. ZERO, which translates to a level ZERO PPE requirement...

I guess this means that if you short circuit grounded metal, you get zero current and therefore zero incident energy. This doesn't take into account what happens if there is an arc behind the covers. The arc can move, vents allow energy through, covers can blow off, etc. There's no way to calculate the energy. NFPA 70E 130.7(C)(9) FPN No. 1 says that the collective experience of the task group is that closed doors don't provide enough protection to eliminate the need for PPE.

 

[mshields]

a bit confused

a bit confused

So it's not an NEC code requirement but a label with PPE level on it, is required by OSHA. As an engineer I run into alot of facility guys who don't want anything to do this if they can avoid it. I'm often adding a single new switchboard to an existing system for which no Arc Flash study has been done and on which there are no labels. They want to keep it that way.

That I should recommend a label beyond the NEC requirement of a generic label is clear. But am I required to get arc flash warning with specific PPE level on the new switchboard that I specify? Must I insist on this for my client.

Thanks,

Mike

 

[zog]

So it's not an NEC code requirement but a label with PPE level on it, is required by OSHA. As an engineer I run into alot of facility guys who don't want anything to do this if they can avoid it. I'm often adding a single new switchboard to an existing system for which no Arc Flash study has been done and on which there are no labels. They want to keep it that way.

That I should recommend a label beyond the NEC requirement of a generic label is clear. But am I required to get arc flash warning with specific PPE level on the new switchboard that I specify? Must I insist on this for my client.

Thanks,

Mike

Not OSHA (Directly anyways) bu t the NFPA 70E 2009 edition requires all equipment to have either the Ei or the PPE necessary to work on the equipment, the owner is responsible for this.

 

[mayanees]

I guess this means that if you short circuit grounded metal, you get zero current and therefore zero incident energy. This doesn't take into account what happens if there is an arc behind the covers. The arc can move, vents allow energy through, covers can blow off, etc. There's no way to calculate the energy. NFPA 70E 130.7(C)(9) FPN No. 1 says that the collective experience of the task group is that closed doors don't provide enough protection to eliminate the need for PPE.

Not dissenting this point at all. I say use the "covers-on" value from the table.
Stay tuned because I will get to the bottom of this asap. I think my approach is a safe one: open bus-use calcs; covers on - use tables (because I can't calc the incident energy acroos the sheet steel covers!).
But I'm only looking for the answers, because I don't have all of them. I certainly stand to be corrected if and when appropriate.
John M

 

[mshields]

Found a great article on the subject

Found a great article on the subject

C:\Documents and Settings\mshields\My Documents\Technical Info\arc flash\NFPA 70 vs 70E.mht

This link clarifies the roles of 70, 70E and OSHA very clearly.

Mike

 

[mayanees]

Stay tuned because I will get to the bottom of this asap. I think my approach is a safe one: open bus-use calcs; covers on - use tables (because I can't calc the incident energy acroos the sheet steel covers!).
But I'm only looking for the answers, because I don't have all of them. I certainly stand to be corrected if and when appropriate.
John M

I've pored over NFPA70E Article 130, and I've polled 3-4 EEs, all of whom, if not initially, at least ultimately, agreed with the above-listed interpretation.

But of course that topic led to further discussion. Our focus went to the electrician who is ultimately faced with PPE selection when he encounters a board. Some thought it would be valuable to state on the Arc Flash Warning label that this PPE requirement applies to exposed bus. But that argument was countered with the Qualified Persons definition in 70E, which states:
One who has skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training to recognize and avoid the hazards involved.
A qualified person would know to go to Table 130.7(C)(9)(a) for PPE requirements on work that does not expose the bus.

I pose the question to you guys. If you're sent in to work on an energized 480V MCC that is labelled with a specific Hazard Risk Category, and you want to operate the meters to check Voltage and Current, do you suit up in Level 2 gear, or do you go to the table where it states that level 0 PPE is required, and then operate the meters accordingly?? Or do you just skip the words in italics?? (I know many industrials provide Level 2 PPE as general issue uniforms.)

I've been strolling up to 480 Volt MCCs forever, and checking the meters, just as a matter of interest. And I was glad to see that it's still okay to do that per the Table.


John M

 

[neutral]

Being a trained and qualified Industrial Electrician working around 480, 4160 and 33000 volts for 30 years I know the dangers of working around live equipment. I use common sense and protect myself accordingly. Labels are only good for the untrained and not qualified. We had standard maintenance manuals that listed the PPE needed for jobs performed around high voltage above 480 volts. Engineers and supervisors? unless the supervisor was a trained and qualified electrician before becoming a supervisor were not allowed to touch anything electrical, if they needed information they would have to schedule an Electrician to perform the work for them.

 

[diakonos1984]

Covers on or off?

Covers on or off?

Anyone who's ever seen an arc flash burn up would agree that the grenade-type explosion doesn't care if the covers are on or off! It's gonna blow big! If you have an HRC 3 with an arc flash boundary of 49 inches on a 480V system, it's gonna blow the cover clear off the hinges and to the wall on the other side of the aisle! Remember we're talking copper plasma expanding to tens of thousands of times its original volume. The explosion also doesn't care if you're working on the energized parts or just walking through.

Case in point:
One of our customers is a bad customer... and never lets us in for preventative maintenance--just for burn down clean up! They had an MV motor starter that hadn't been serviced in years, and the finger clusters on the back started falling apart. Eventually, there was enough gap and not enough conductor, and an arc flash incident occurred. I don't know what the HRC was at this point, because this customer also wont let us do studies, but the whole room was blackened by the explosion. And not just the door hit the opposite wall, the starter was sent across the room.
Good thing the motor was remotely started, and no one was even in the room. But tell me, if you were in front of the starter "reading a panel meter while operating a meter switch" do you think the table's HRC 0 PPE would have protected you?

I personally don't like the NFPA tables. They're based on gambling. As in this case, arc flash incidents can occur because of things you're not even aware of when your not even performing work on energized equipment! We don't determine our fall protection by the strength of the ladder, or how many tools we're carrying in our tool belt, or how wide the girder we're walking out on is... don't play probability games! You wear a harness if there is ANY possibility of falling.

I want to be protected for the maximum possible arc flash at the given location. And because that is a function of fault current and device operating time, you can't tell by looking what that's going to be. You've got to calculate it! Now flash containing gear may be a different matter, but that's a newer innovation, and primarily only used in MV equipment, and I typically see more high category locations on LV equipment.

My personal opinion is that the table should never take the place of a full study, but should only be used in the interim period while the study is being performed. Not only will the study give you worst case results, it will also give you the tools to devise a way to lower the results. You should be able to get any 480V MCC with a main breaker down to a HRC 2 or below. Most can be HRC 1 or 0.

At the bottom line, it becomes a personal matter. And that is part of the purpose of NFPA-70E anyway--to remind the guy working on the equipment that he has a responsibility too! I think the standard gives some leeway regarding covers and the nature of the work, but the calculations don't. They present the worst case scenario. It's up to you if you want to play odds.

Personally, I would check meters all day in jeans and a long sleeve shirt. But I would never tell someone else that it is safe to do so. I have assumed the risk and accepted the odds. If that starter goes out while I'm standing here, I'm toast!

Anyway, there's my opinion on a subject where the standard has obviously left a lot of room for opinions!

 

[zog]

Great post Nathaniel, welcome to the forum.

 

[billsnuff]

NEC label:

NFPA 70E label:

 

[mayanees]

...okay

...okay

I personally don't like the NFPA tables. They're based on gambling. As in this case, arc flash incidents can occur because of things you're not even aware of when your not even performing work on energized equipment! We don't determine our fall protection by the strength of the ladder, or how many tools we're carrying in our tool belt, or how wide the girder we're walking out on is... don't play probability games! You wear a harness if there is ANY possibility of falling.

I want to be protected for the maximum possible arc flash at the given location. And because that is a function of fault current and device operating time, you can't tell by looking what that's going to be. You've got to calculate it! Now flash containing gear may be a different matter, but that's a newer innovation, and primarily only used in MV equipment, and I typically see more high category locations on LV equipment.

My personal opinion is that the table should never take the place of a full study, but should only be used in the interim period while the study is being performed. Not only will the study give you worst case results, it will also give you the tools to devise a way to lower the results. You should be able to get any 480V MCC with a main breaker down to a HRC 2 or below. Most can be HRC 1 or 0.

At the bottom line, it becomes a personal matter. And that is part of the purpose of NFPA-70E anyway--to remind the guy working on the equipment that he has a responsibility too! I think the standard gives some leeway regarding covers and the nature of the work, but the calculations don't. They present the worst case scenario. It's up to you if you want to play odds.

Personally, I would check meters all day in jeans and a long sleeve shirt. But I would never tell someone else that it is safe to do so. I have assumed the risk and accepted the odds. If that starter goes out while I'm standing here, I'm toast!

Anyway, there's my opinion on a subject where the standard has obviously left a lot of room for opinions!

-----------------------------------------------------------------------
And you are entiled to your personal opinion. As a registered engineer, I have to interpret the code, and advise accordingly, without any personal bias. I have an obligation to my client and to the electrician's to engineer a system or procedure that is in compliance with the regulations - nothing more, nothing less. DuPont uses the term "minimum essential" and that's what I engineer for.
Then I rely on the work done by the committees that developed the regs - and I provide my interpretation. My interpretation is always open to scrutiny, and I welcome it from other interpretors.

John F. Mayan, P.E.

 

[mayanees]

PPE Update

PPE Update

Not dissenting this point at all. I say use the "covers-on" value from the table.
Stay tuned because I will get to the bottom of this asap. I think my approach is a safe one: open bus-use calcs; covers on - use tables (because I can't calc the incident energy across the sheet steel covers!).
But I'm only looking for the answers, because I don't have all of them. I certainly stand to be corrected if and when appropriate.
John M

In the interest of technical correctness, I'm posting my assessment to PPE requirements around equipment - based on my recent investigation.

(And this point has been made by several posters, but it took some learning to get it into my head. (smile Zog))

The current state of Arc Flash Hazard calculations is such that once a Hazard Risk Category has been determined by calculation, that's the level of PPE required anywhere within the calculated Arc Flash boundary, doors on or off. The rationale is that if the bus has a given Incident Energy, then closing the doors on it won't shield you from that energy, and in some cases could exacerbate the problem - i.e. if pressure builds up in an enclosure until it explodes.

Apparently the IEEE 1584 Committee is still working on improving the analysis, but for now I can't advise a facility owner that it's safe to operate a panel meter on an MCC while wearing PPE level zero (per tables), if I've calculated a higher level for the exposed bus.

I stand corrected.

John M

 

[charlie]

Don't forget 110.10 Circuit Impedance and Other Characteristics. The overcurrent protective devices, the total impedance, the component short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit-protective devices used to clear a fault to do so without extensive damage to the electrical components of the circuit. . .

That makes me wonder at your statement, ". . . then closing the doors on it won't shield you from that energy, and in some cases could exacerbate the problem . . ." Really, then is the equipment selected and installed correctly?:smile:

 

[mayanees]

Don't forget 110.10 Circuit Impedance and Other Characteristics. The overcurrent protective devices, the total impedance, the component short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit-protective devices used to clear a fault to do so without extensive damage to the electrical components of the circuit. . .

That makes me wonder at your statement, ". . . then closing the doors on it won't shield you from that energy, and in some cases could exacerbate the problem . . ." Really, then is the equipment selected and installed correctly?:smile:

My comment about closing the doors references the hypothetical case where a cabinet, if sealed, could overpressure and come apart. I've been told by Mr. ArcFlash Forum that one switchgear manufacturer filmed non-arcflash-resistant switchgear doors blowing off at 600 mph.

 

[jim dungar]

Don't forget 110.10 Circuit Impedance and Other Characteristics. The overcurrent protective devices, the total impedance, the component short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit-protective devices used to clear a fault to do so without extensive damage to the electrical components of the circuit. . .

That makes me wonder at your statement, ". . . then closing the doors on it won't shield you from that energy, and in some cases could exacerbate the problem . . ." Really, then is the equipment selected and installed correctly?:smile:

110.16 says, equipment must be able to withstand a thru fault until the protective device operates. But what if the fault occurs internal to the equipment (i.e. on the bus of a panel or switchboard)? The equipmnet is the fault, therefore how can it be able to withstand the arc, unless it is arc-resistant gear? While the arcing equipment is waiting for the protective to operate, the proper PPE must be worn by any one standing in the 'arc flash area'.

 

[zog]

110.16 says, equipment must be able to withstand a thru fault until the protective device operates. But what if the fault occurs internal to the equipment (i.e. on the bus of a panel or switchboard)? The equipmnet is the fault, therefore how can it be able to withstand the arc, unless it is arc-resistant gear? While the arcing equipment is waiting for the protective to operate, the proper PPE must be worn by any one standing in the 'arc flash area'.

I was about to post the exact same thing, great minds....

 

[jim dungar]

I was about to post the exact same thing, great minds....

But, I feel that interacting with a dedicated/isolated 120V metering compartment is not the same as interacting with other parts of the equipment. For example, in a two high section of MV switchgear where the bottom cubicle is a breaker and the top one is dedicated to metering, the 120V metering compartment could have a HRC=0 (it is fed by a transformer <125KVA) while the breaker cubicle could have a different one. This would not be the case however in equipment, like a switchboard, where the metering is barriered but not isolated.

The important thing is the existence of an Electrical Safe Work Practice program, that deals with these issues and procedures, not simply the presence of an 'arc flash' sticker.