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 Post subject: Is operation of circuit breaker handle a system interaction?
PostPosted: Mon Feb 20, 2012 7:08 am 

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In a context of remote opening and closing of a high energy breaker, would the cycling of the handle require PPE? In my mind, there's enough torque being applied to a housing/panel/switchgear unit to at least brainstorm whether or not the exposure warrants PPE? Any thoughts on the matter would be appreciated.


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PostPosted: Mon Feb 20, 2012 7:22 am 
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Unless your equipment is arc rated switchgear you should wear the PPE required on the arc flash study label, or the HRC from the task tables if no study has been performed. The definition of arc flash hazard refers to the task tables for examples of interactions.

A new note that discusses properly maintained equipment that is enclosed as not being a hazard added confusion IMO, it put the decision of weather or not an enclosure will contain an arc (Which it was never designed to do) on the equipment owner. Tough call to make for those who have to make it, but if you are missing panel screws or have openings like vents it seems obvious to me.


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PostPosted: Mon Feb 20, 2012 8:01 am 
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NFPA 70E mentions interaction likely to cause an arc, not just simple interaction.

The question you need to feel comfortable with is: Will this operation result in a failure of the device being operated.
Clearing and managing the energy from a downstream fault is part of the normal test procedures for determining AIC ratings. Containing an internal fault is not part of any routine product testing.

Inherent in all arc flash procedure is the assumption that an upstream protective device will operate properly. If, instead, we assume all protective devices could fail any time they operate then why bother with the whole process?


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PostPosted: Mon Feb 20, 2012 9:24 am 
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Arc containment is a tricky discussion legally that might be subject to the equipment class and manufacturer's reputation (subjective). I have engaged this discussion with 3 large manufacturers of switchgear, some of which offer "closed door racking" as an option on their non arc rated switchgear. Even on non arc rated equipment, I believe ANSI standards require some kind of enclosure testing to contain the rated arc wthstand.

The exact wording of "exposure" seems to take priority; one can calculate a HRC for equipment that due to its construction distances and dialelectric strength cannot sustain an arc.

Few are willing to say PPE is not needed, yet the solutions they sell would have no value if there was exposure. I have only been able to answer this question individually on specific installations that we were able to obtain documentation from the major manufacturer.


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PostPosted: Mon Feb 20, 2012 10:40 am 
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Quote:
Even on non arc rated equipment, I believe ANSI standards require some kind of enclosure testing to contain the rated arc wthstand.

On non arc rated equipment there is no rated arc withstand.

NFPA 70E more or less leaves it up to the company to determine risks if the incident energy is calculated instead of using the task tables. On the one hand, the new informational note in 130.7(A) inticates that normal operation of enclosed equipment is unlikely to cause a hazard, racking a breaker may not be considered "normal operation". On the other hand, the fact that this has a Cat 4 HRC in the task tables indicates that there is a hazard. IMHO, racking breakers should require the PPE calculated for exposed arcs and it should not make any difference if the racking is done with the doors closed if the switchgear is not arc rated.


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PostPosted: Mon Feb 20, 2012 8:23 pm 
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Seems there is some confusion about racking vs. opening/closing. It sounds as if the 70E Technical Committee is specifically referring to operating meaning opening/closing and not racking. Perusal of the ROP's indicates this many times over.

I've read a recent paper written by the sales people at ABB that suggested that 75% of failures of switchgear is in the racking mechanism and not the breaker itself. Wish they had footnoted it more than that because we've been having that same discussion where I work.

Perusal of IEEE 493 (Gold book) points out some more interesting data. Rack-out gear is roughly 10 times more likely to fail than bolted gear. The data on vacuum breakers is really, really old. However, Powell reported a couple years back that they've logged over 20,000 hours average with no VCB failures.

Further perusal of the same data set points to that only about 11% of the failures of breakers occur during normal operation in the worst case scenario (fails while opening and fails to open, or fails while closing). Either way since the failure rate data is given, it is also very easy to apply the maintenance inspections to it to determine the probability of a dangerous failure occurring and not being detected during routine inspection and cleaning.

The numbers that I've calculated seem to show that without adequate maintenance (meaning inspections at least every 3-6 years, and exercise annually), that the risk of failure exceeds the typical "1 in a million" category. Otherwise when operating breakers of any type (except racking) the risk of a failure statistically appears to be better than 1 in a million.

Not sure that this helps but I''ve run the numbers a couple different ways and keep coming to the same conclusion that the risk of an exposure during operating of a breaker assuming that proper maintenance is being done is very low. However if you don't do the maintenance then the risk becomes unacceptable with even very mild assumptions.

Using probabilistic risk assessments by the way is in my opinion what belongs in the 70E appendix, not what was there in the 2009 version or the 2012 version. Neither one seem to follow any accepted standard and neither one are very workable.


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PostPosted: Tue Feb 21, 2012 6:59 am 
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EPRI has a ton of data on breaker failures, the stats vary a little from model to model but lubrication issues is by far the most common breaker failure with average failures somewhere in the 9 year range. To properly lubricate a breaker requires complete disassembly of the mechanism, you can't add oil to the grease and that "tech in a can" spray lube some people use only makes matters worse. That is why nuclear plants are required to refirbish thier breakers every 10 years.

NETA has been doing a project for years gathering failure data on breakers, there is a seminar on the findings at Powertest next week in Dallas I will be attending.

VCB bottle failures are becoming more and more common as most bottles were designed with a 20-30 year life span, and with VCB technology showing up commonly in the 1980's many VCB's are right there. In the past there was no way to test bottles in the field besides a go-no go hipot test, now there is technology available to field test for pressure in the bottles to predict life expectancy.


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PostPosted: Tue Feb 21, 2012 8:31 am 
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We need to do a better job clarifying what equipment we are discussing. A switch means something different to 'residential' electrician than it does to an operator at a nuclear plant. Sometimes adjectives and adverbs can change the entire meaning of the discussion.

Miniature molded case breakers, molded case power breakers, drawout 'maintainable' breakers, vacuum breakers - all have extremely different maintenance and operation issues, but everyone wants a single operating answer that covers all breakers.

A 30A 600V non-fused disconnect almost never fails in a manner that would cause a fault even if it has not been operated or maintained for decades, however a 5000A bolted pressure switch almost always develops operation issues when not maintained in as few as 3 years.


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PostPosted: Tue Feb 21, 2012 7:23 pm 
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I agree about needing to know what we are talking about. The same problem happens everywhere especially in the safety arena. However the problem is that the data that we're all after is a problem of "small number" statistics. It takes a long time to get real world data (waiting for failures to happen) and we need it not to be anecdotal in nature. And technology advancement does a heck of a job skewing the results. Today's vacuum bottles are not the same design as those even 10-15 years ago, and neither are the trip relays. So data comparison over time is not very good. Sometimes this results in invalidating whole categories of equipment as well. If you look at the IEEE 493 data for vacuum breakers, it looks like they are worse than their air counterparts, but a closer examination shows that the number of hours in the database is very small and the number of failures is nonexistant, so the data itself is suspect. VCB failure rates are significantly better than the data would indicate.

In some arenas it is possible to do theoretical/calculated results (especially electronics that can rely on the military databases) but not in others.


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PostPosted: Sun Mar 18, 2012 10:53 am 
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JBD wrote:
We need to do a better job clarifying what equipment we are discussing. A switch means something different to 'residential' electrician than it does to an operator at a nuclear plant. Sometimes adjectives and adverbs can change the entire meaning of the discussion.

Miniature molded case breakers, molded case power breakers, drawout 'maintainable' breakers, vacuum breakers - all have extremely different maintenance and operation issues, but everyone wants a single operating answer that covers all breakers.


I think the title of this thread says exactly with the OP is asking about - "circuit breaker handle" to me means the handle on a low voltage molded case circuit breaker (MCCB), the type covered by UL 489.

The question seems to be then, very specifically, whether operating the handle of a UL489 MCCB is likely to cause an upstream fault or downstream fault. I believe the 70E committee was trying to address this specific questions when they wrote the new informational note in 130.7(A) that indicates that normal operation of enclosed equipment is unlikely to cause a hazard.


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PostPosted: Sun Mar 18, 2012 4:09 pm 
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Properly maintained equipment. That is the key, when is the last time this breaker was tested? How about at least inspected? How many times has this breaker interupted a fault? Has it exceeded its design number of fault interuptions? (Which is usually only a couple of times)

These are key factors and the reason 70E won't give a black and white answer.


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PostPosted: Mon Mar 19, 2012 6:08 am 
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Statistics on the probability of a breaker failing to interrupt a fault are not relevant to the question of the safety of operating the breaker. If the breaker fails to interrupt a fault but doesn't fail catestrophically, then the safety issue, if any, is at the fault where the clearing time is higher than calculated. If the breaker fails catestrophically while interrupting a fault, there is no safety issue if no one is near the breaker when it fails. The relevant statistic would be how often the breaker would fail and cause an arc flash at the breaker during manual operation of the breaker, whether it was interrupting a fault or not. Now we're really talking about "small number" statistics. If it is more likely to fail catestrophically while interrupting a fault, then you have to also determine the probability of a fault occurring at the instant of manual operation of the breaker.


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PostPosted: Fri May 18, 2012 5:14 am 

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I appreciate this discussion very much. As a superintendent of a wastewater treatment facility we looked at our original ARC Flash study ratings for protection of our electricians. When the 2012 update came out are Safety Department started looking at the ratings differently. We assumed that ratings of "O" meant that I could train non electrical employees to operate at this level with minimal PPE, (cotton clothing, leather gloves and face protection." Not arc flash rated clothing. We also have to lock out breakers (MCC's 480V, 3 phase) to perform maintenance on the equipment, not the breaker. I have a few 480 breakers with an ARC Flash rating of 2. I think we can use Annex F of the 70E to perform a risk assessment to allow my Operators to open and close a breaker for lock-out tag out. We have a very good preventive maintenance system for our electrical systems. Supplying all 29 employees Arc flash rated clothing to lock-out equipment that even the code states is a minimal hazard seems excessive but if that is where we need to go I want to be sure we have looked at all our options. I was wondering if anyone has actually performed a risk assessment for this purpose?


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PostPosted: Fri May 18, 2012 8:03 am 
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Warning: do not take these procedures out of context. They are part of an overall Electrical Safe Work Practices Program.
Basically our company's procedures are:
Opening of a circuit that has been operating can be done as Cat 0, by someone qualified in LOTO. (allows LOTO of a machine that has been running).
Closing a circuit that was previously operating can be done as Cat 0 if no electrical work has been done, by someone qualified in LOTO (allows removal of LOTO and restart after mechanical servicing).
Closing a circuit that was previously operating must be done by a 70E qualified worker, based on calculated AFIE if any type of electrical work has been done (i.e. replacing a motor).
Closing a circuit whose status is unknown (i.e. resetting a tripped device) must be done by a 70E qualified worker, based on calculated AFIE.


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PostPosted: Fri May 18, 2012 8:17 am 

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Thank you for the reply. Your comments about changing a motor is a good one. I think this will help greatly as we try to document are procedures. I think it is a very safe approach as long as we train the employees to use all safe practices when they are locking out a breaker. I appreciate you time.


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PostPosted: Fri May 18, 2012 6:38 pm 
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Where I work one division did the risk assessment and determined that opening/closing breakers is "normal operation" and can be done safely. Another division came to a different conclusion. I might also add that one division had electrical folks on the committee and the other one was entirely made up of consultants and safety personnel.


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PostPosted: Wed May 23, 2012 9:19 am 

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JBD wrote:
Warning: do not take these procedures out of context. They are part of an overall Electrical Safe Work Practices Program.
Basically our company's procedures are:
Opening of a circuit that has been operating can be done as Cat 0, by someone qualified in LOTO. (allows LOTO of a machine that has been running).
Closing a circuit that was previously operating can be done as Cat 0 if no electrical work has been done, by someone qualified in LOTO (allows removal of LOTO and restart after mechanical servicing).
Closing a circuit that was previously operating must be done by a 70E qualified worker, based on calculated AFIE if any type of electrical work has been done (i.e. replacing a motor).
Closing a circuit whose status is unknown (i.e. resetting a tripped device) must be done by a 70E qualified worker, based on calculated AFIE.


JBD-from your statement above you are saying that if you open a circuit they only have to be LOTO trained? I hope that is not what you are saying. If you are opening a circuit that has the ability to create an arc flash defined by NFPA 70E then you need to have the proper PPE donned and they need to be qualified workers which would require training and experience. The only way that I think you may have an arguing point is if you maintenance and maintain this equipment and document this per the manufacturer. If a worker opens the circuit and and arc flash occurs and you have a fatality or burn-how would you defend that to OSHA or a court of law?


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PostPosted: Wed May 23, 2012 11:31 am 
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jcampbell wrote:
If you are opening a circuit that has the ability to create an arc flash defined by NFPA 70E then you need to have the proper PPE donned and they need to be qualified workers which would require training and experience.


Why would manually opening an operating circuit cause an arc flash, except in the situation where the switching device failed?

NFPA70E provides for the employer to create standards for qualifying workers to specific limited tasks, such as opening a circuit for LOTO purposes.

Why would this be hard to defend in a court of law?
The NFPA70E committee addresses this issue in their Information Note #2 to 130.7(a).
This is part of the rationale behind the Task Tables 130.7(C)(15)(a).
Risk assessment is part of NFPA70E 110.3(F)

I began my post with a specific warning not to take it out of context. The procedures I posted are part of a complete Electrical Safe Work Practices program which our 'risk management' team was involved in creating.

NFPA70E is purposely written in "shades of gray" for what must be accomplished, not in 'black and white' for how to do it.


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PostPosted: Wed May 23, 2012 8:39 pm 
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jcampbell wrote:
If you are opening a circuit that has the ability to create an arc flash defined by NFPA 70E then you need to have the proper PPE donned and they need to be qualified workers which would require training and experience. If a worker opens the circuit and and arc flash occurs and you have a fatality or burn-how would you defend that to OSHA or a court of law?


This is far simpler than you make it sound. Within 70E, there are two different methods for doing a risk assessment. The specifics are different, but the same procedure is also given in IEEE C2 (NESC).

Method 1: For the specified task, locate the task in the task tables in 70E (or the task tables in NESC 2012 version). Check that the equipment design is less than the minimum requirements (trip time, bolted fault current, and voltage limits). If so, then use the PPE specified in the table.

Note: Table was developed by first calculating the incident energy using IEEE 1584. Then the task was examined for likelihood and the incident energy value was adjusted by a risk assessment committee made up of NFPA 70E members.

Method 2: Perform a risk assessment. NFPA 70E does not specify the specific method for doing so. IEEE 1584 provides a worst case incident energy value but does NOT provide likelihood of occurrence. Almost all modern risk assessment methodologies (PMMA, IEC 61508, IEC 61511, RIA, ANSI B11.TR3, etc.) look at both the severity of the injury and the likelihood of occurrence. Based on a risk ranking matrix, either further risk reduction is recommended or no additional requiremnts are needed. Using any of these methodologies, PPE would only be required if the risk reduction matrix result recommended further reduction.

This means that in cases where an arc flash hazard is possible but that the likelihood of occurrence is low (defined by the risk assessment methodology), no further action is necessary. OSHA has routinely used quantitative risk assessment methods to determine if there is significant risk of injury. A quick search on OSHA's web site returned 58,800 references to quantitative risk assessments. Risk assessments are almost a de facto requirement, whether they are performed quantitatively or not these days.

Second, in your alluding to the idea of maintaining equipment properly...again, this is pretty much a requirement. The reliability of the equipment rapidly degrades within a few years if this is not done. The result with circuit breakers is usually that they are unlikely to trip. With disconnects, it is likely that they will fail to open or worse, arc as they open. NFPA 70E clearly states that the results of the analysis are meaningless if proper maintenance is not being done. In the plant I work at with 1200 buses, I ran the arc flash hazard calculation except that I extended the opening time for circuit breakers from whatever it was to 2 seconds to simulate a "failed breaker" condition. When I did this, the number of buses exceeing 40 cal/cm^2 went from around 15% to over 50%. Clearly just wearing PPE is simply not adequate protection. BUT that's not to say that some equipment can't be operated without wearing PPE.

Finally, the idea that workers must be qualified "electrical workers" is silly. Workers must be trained to perform LOTO. That makes them qualified to do that specific task. This doesn't mean that they're qualified to open up live panels and do work on live equipment. It simply means that they are trained to perform a certain set of tasks. As an example, I am not qualified to perform live-line, bare-hands work on energized overhead lines. BUT I'm qualified to do a lot of other electrical tasks on energized equipment. I did not see any suggestion that the original poster was looking to allow workers to operate beyond the limits of their training. But they need not be electricians or linemen just to perform LOTO. That's why we have Subchapter J lockouts, Subchapter O lockouts, Subchapter R lockouts, and Subchapter S lockouts under 1910, never mind lockouts performed under 1926. LOTO is not one-size-fits all. If it were, OSHA wouldn't have 4 different LOTO procedures just within 1910.


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