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 Post subject: Breaker Testing
PostPosted: Fri Jul 06, 2007 4:43 pm 
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Do any of you consider if the breaker will actually trip according to the published time current curve? What does everyone do about this?


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PostPosted: Sun Jul 08, 2007 5:40 am 
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I think most people just base the study on the published time current curve. We test larger breakers every few years so hopefully they would perform as expected.


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PostPosted: Sun Jul 08, 2007 9:33 am 
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JH has good comments but there is another way to deal with it as well. When performing the study by computer, play "what if" with the clearing times. See what happens if a device takes twice as long to operate in the calculations. If you still end up with the same category of protection, you can breath a little easier. If the slower time makes a big difference - which it might since incident energy is dependent on clearing time, you might want to rethink the PPE selection or else test the devices. If the devices do not respond exactly as the time current curves indicate, you can bet they will probably be tripping slower.


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PostPosted: Wed Aug 08, 2007 3:55 am 
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Equipment Testing

The International Electrical Testing Association - NETA provides good standards for equipment testing proceedures as well as testing intervals. Although not directly part of the arc flash study, makeing sure your devices still function is quite important.


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PostPosted: Tue Oct 02, 2007 7:36 pm 
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breaker malfunction

The last place I worked at there was no breaker maintenance program enforced on aging breakers. As a result, I was unable to consider this in the arc flash study, except to use some slightly more conservative clearing times. This did not really help the problem, because in most situations, it was found that breakers were failing altogether. Using a 2 second time, resulted in Category 4 clothing across the board mostly (240V and above).

Management did make a decision, as a result, to start a Breaker Maintenance program. I think this is the common-sense solution. It is money better spent than drilling down to a specific answer in an arc flash study, where the results are no good; go with a conservative estimate or NFPA 70E tables when clearing times are uncertain seems appropriate to me, until the problem is solved.

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PostPosted: Sun Oct 28, 2007 1:29 pm 
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Breaker clearing time is a critical attribute determining the energy dispersed during fault clearing. That in turn determines system protection, coordination, and what the breaker is rated at (i.e.: AIC). If you feel a breaker might operate slower than design, there may be greater perils than calculated arc flash exposure.

Medium voltage breakers are routinely 'profiled' wherein the clearing time is verified.

If the clearing time doesn't match spec, the breaker should be removed from service.

I agree with estimating conservative clearing times if specific breaker information is unknown, but if there is some doubt that a breaker will clear per its design the system should be deenergized. I don't believe a slow breaker will survive a fault condition.

Gary B


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PostPosted: Wed May 07, 2008 12:13 pm 
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Proposed Changes

One of the proposed changes to 70E for the 2008 revision is requiring testing and service of electrical systems prior to the arc flash analysis. If I get any further information on the revision, I will post it here. Rumor is the 08 revision may be held up to 09.


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PostPosted: Tue May 13, 2008 9:42 am 
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The 08 version is suppose to be out later this year. It does reference testing of equipment. Too many people think that just because a time current curve indicates a device is suppose to trip in a specific amount of time does not mean that it will. Especially if it is old, untested, and not properly maintained.


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PostPosted: Tue May 13, 2008 5:41 pm 
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Are we talking about switchgear breakers or molded case breakers. To test every molded case breaker in a large manufacturing complex would cost $50 to $100 thousand dollars and entail a week of downtime. How often would this be required? Can you say "my job got moved to China".


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PostPosted: Wed May 14, 2008 5:00 am 
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Hi Everyone,

Yes, I have heard / seen similar changes for 2008. Although the 2008 version is not yet final, here is what I have from a few friends on the NFPA 70E Committee:

130.3 FPN
Improper or inadequate maintenance can result in increased opening time of the overcurrent protective device, thus increasing the incident energy.

205.3
General Maintenance Requirements. Overcurrent protective devices shall be maintained in accordance with the manufacturers' instructions or industry consensus standards.

210.5 FPN
Failure to properly maintain protective devices can have an adverse effect on the flash hazard analysis incident energy values.

Two of the items are fine print notes. I assume 205.3 is taking into consideration testing standards like NETA.

There are a few other major proposals that I will add to a separate posting.

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PostPosted: Wed May 14, 2008 8:28 am 
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It sounds like testing is going to become part of the process. I understand why it is included but this will be quite a burden on some companies. Haze - I don't think there is much you can do with molded case breakers except switch them on and off to see if they still open / close - maybe an IR scan too. It's amazing how many older breakers have never even been operated. Switchgear breakers will likely fall under this rule. I have been to many places where they have never tested anything assuming "something will trip" if there is a fault. That "something" is sometimes the utility fuse.


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PostPosted: Wed May 14, 2008 1:54 pm 
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This is a follow up to my earlier post about breaker testing. I dug up some data from a conference I attended earlier this year. A survey was conducted of NETA companies (testing) about the condition of breakers. It included a review of 340,000 electrical protective devices. The survey results were alarming to say the least.

22% of breakers tested had an issue with operation meaning they did not perform as expected

10.5% of devices did not function at all when tested.

Lubrication was one of the predominant mechanical failure issues at 51.4%. I have seen this often myself.

Since incident energy is directly proportional to the duration, device operation is a major issue.

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PostPosted: Thu May 15, 2008 12:38 am 
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Breaker malfunction

Hi everyone, I'm a UK based Electrical Safety Consultant and would like to share an experience that I had some years ago which related to a breaker malfunction. I was called to give evidence in a trial against an electrician who was involved in an arc flash incident involving a 200 amp fixed pattern breaker with a non adjustable magnetic and thermal overload element. (These are in common use here up to several hundred amps rating) He was changing a faulty three phase capacitor which was fed by the breaker. The breaker had tripped under fault but one of the phases had failed to clear because the contacts had welded in the closed position. The electrician failed to carry out correct isolation procedures. (I think that he did test for voltage but only used his test lamps between the phases and not phase to ground) The result was an arc flash which injured his colleague and resulted in hospital treatment.

What I discovered then, which was not fully understood at the time, is that this type of circuit breaker was not designed to interupt fault current time after time and faithfully maintain it's time current characteristic. It was actually a "one shot" device much like a fuse.

Lessons learnt

1. Make sure that electrical workers follow proper LOTO procedures.
2. If you are in charge of a facility it is important to know the tripping history of protective devices.
3. You need to have confidence in the protective devices when undertaking an arc flash study. I know that much has been said on this subject already but do you actually know what will happen to the characteristics of this type of fixed pattern breaker after clearing fault current? It might be worth asking the question.

Mike Frain
Electrical Safety UK Ltd
http://www.elecsafety.co.uk


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PostPosted: Sat May 17, 2008 10:52 am 
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I've been maintaining switchgear breakers for 30 years. Frequency of maintenance is most related to environment. In office type air conditioned electric rooms I have reduced the testing schedule to 3 years. Pulling the breakers out they look new, and always test perfect. Other switchgear breakers located in manufacturing areas are caked with dust, dirt, and often shows signs of sticking components - even though they are tested annually. My point is that we again should not have the government, who knows little of manufacturing, be setting the standards. Just more legislation that makes manufacturers want to leave the country.

As for molded case breakers, I remember reading somewhere that molded case breakers are only listed to handle one fault trip and that after that they are supposed to be replaced. Does anyone know if this is true and where that comes from.


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PostPosted: Sun May 18, 2008 12:09 pm 
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The good news (maybe??) is NFPA 70E is a National Consesnsus Standard and not any form of legistlation. (although it sometimes appears to be) That means you, me and everyone in the forum or elsewhere can propose changes for the next revision. In fact, about the only way it does change is for people to make the proposals.

You are correct that I have seen many struggling industries throw in the towel when too much regulatory burden is forced on them. I am hoping the intent of the 2009 change about testing was just to bring the issue front and center since many companies have the "it worked when we installed it in 1978" logic when it comes to testing. They sometimes think it will still work as good as new 30 years later without proper testing and mainenance. Hopefully there won't be an over reaction where it is unwarranted but at least prompt some kind of reaction where testing has been ignored.

The circuit breaker being only good for one shot is a propaganda line that has been floating around for a very long time. When U.L. short circuit tests a breaker, it is at it's maximum rating and the breaker has to be able to be reset and calibrate correctly. This is only done once and not repeated. It says nothing about whether the breaker can or can not take a second shot, only that the test involves one interruption. From that, certain companies that don't like breakers have twisted the logic getting people to think breakers are only good for one hit.

That would be like saying an NBA player went to the free throw line only once and made the basket but never went to the line again. Does that mean he is physically not capable of ever making a basket again? No, he just never had a second opportunity.

Also, most short circuits are not maximum faults - typically they are lower magintudes due to branch circuit impedance etc. I have seen quite a few breakers being reset after faults and they still perform fine.

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PostPosted: Wed May 21, 2008 7:37 am 
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Good info about the breaker testing. I have heard the same story about breakers only being good for one shot - I always thought that was odd and did not make much sense.


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PostPosted: Fri May 23, 2008 9:46 am 
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Maintenance

I sense a that OSHA will address maintenance of all equipment soon. The arc-flash studies are based on best case scenarios. All equipment working properly. Batteries, relays, cable, breakers, etc.
[color="Red"] NFPA 70b "Recommended practice for Electrical Equipment Maintenance 2006 edition". [/color]
This is where OSHA will point when something happens because of poor equipment performance.
Get a copy and see where you need work. I have been giving a 2 day course based on this book and it has gone over well to non-electrical Supervisors and Facility Management personnel. It tells how to set up a maintenance program, how to administer it but most important , it lets you determine when to stop doing scheduled maintenance on equipment yourself and hire someone. Why qualify in house mechanics for tasks done less often than economically feasable? Relay calibrations and breaker PM's to name two.
Arc-Flash studies and PPE are just the first steps in creating a reliable and safe workplace.


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PostPosted: Mon Jun 02, 2008 12:03 pm 
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haze10 wrote:
I've been maintaining switchgear breakers for 30 years. Frequency of maintenance is most related to environment. In office type air conditioned electric rooms I have reduced the testing schedule to 3 years. Pulling the breakers out they look new, and always test perfect. Other switchgear breakers located in manufacturing areas are caked with dust, dirt, and often shows signs of sticking components - even though they are tested annually. My point is that we again should not have the government, who knows little of manufacturing, be setting the standards. Just more legislation that makes manufacturers want to leave the country.

As for molded case breakers, I remember reading somewhere that molded case breakers are only listed to handle one fault trip and that after that they are supposed to be replaced. Does anyone know if this is true and where that comes from.



NETA uses a Reliability Centered Maintenance (RCM) program that takes environmental and reliability requirements in to account. You can download the recommended intervals for free at http://www.netaworld.org

The 1 time thing for MCCB's comes from the manufactures, and only applies for fault interuptions. Or course you have no idea why it tripped if you dont have indicators (Which usually cost extra) so you need to assume any trip was a fault (Vice overload). The IB's dont say they need to be replaced, they just say they are only rated for 1 fault interuption, but smaller MCCB's would cost more to test than to replace, so they usually just get replaced.


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