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 Post subject: arc flash study
PostPosted: Thu Apr 02, 2015 9:26 am 

Joined: Sun Oct 07, 2012 11:15 am
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A co. Hired a rep to have an arc flash study completed at the end of 2112 Not sure 2009 or 2112 cycle. All of the company's electrical equipment went un pm,ed or switchgear calabrated in years.. No work to mcc before the study either.Was this a waste of money for the company ? How should this be handle between rep and engineering?


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 Post subject: Re: arc flash study
PostPosted: Thu Apr 02, 2015 4:23 pm 
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bure961 wrote:
A co. Hired a rep to have an arc flash study completed at the end of 2112 Not sure 2009 or 2112 cycle. All of the company's electrical equipment went un pm,ed or switchgear calabrated in years.. No work to mcc before the study either.Was this a waste of money for the company ? How should this be handle between rep and engineering?


Keep in mind this is not a legal opinion. But I think it's very valuable. Even if you know the answers to the questions outside "experts" can make statements with credibility that is often more acceptable than from inside "experts".

Second lets consider the positive results:
1. All breaker timing information is suspect. But even if all the data is suspect you can still run the calculation out to 2 seconds and assume the breakers simply fail to work and get an estimate of the magnitude of the problem.
2. The risk assessment that should have been done should have identified what equipment was in poor repair and needs something done to it, or is suspect. In other words it lends credibility to doing a PM.
3. It documented short circuit and coordination studies if you didn't already have them, and pointed out deficiencies in this area.
4. Fuses operate off of an electrochemical reaction that is not affected negatively by age of the fuse unlike breakers where lack of lubrication causes them to seize up and operate out of tolerance. So when fuses are involved all the data is accurate and correct.
5. Somewhere along the way the educational value of the exercise cannot be denied.

Just sticking your head in the sand and refusing to do ANYTHING until the PM's are done is simply not an effective strategy. In this case even if it is less than 100% effective an effort was being made to change things to improve safety and/or reliability. To fight against a positive improvement just creates further resistance to improvements in other areas. I'd continue to reiterate the need for PM's throughout the process and make a recommendation that from an overall plant strategy point of view that doing arc flash studies without implementing an effective PM program is getting the cart before the horse, but I have to contend with this all the time. If the result is that the arc flash study is valid if the equipment is working as specified, then we've made one positive step forward. Going back and doing the PM's then makes the study valid and helps build additional credibility for the program, iimproves safety, and improves reliability. Everyone wins. It just might take an outside expert to state that "my report is meaningless unless you do your PM's" to get to that step.


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 Post subject: Re: arc flash study
PostPosted: Fri Apr 03, 2015 4:00 am 

Joined: Sun Oct 07, 2012 11:15 am
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Thank you for the great reply .
My concern is after so many years after the study there is no movement towards pm'img equipment. This timing issue could mean our ppe is not at the right level for protection against a fault? YES/NO? If the timing is off and the cb stays open longer than it should , are we not in trouble ?
We mention this to the company and the answer has always been about the PM cost of getting the work done. "we can t afford it now".
We are looking for ways to push the company into getting this done. It just doesn t seem right to do a study knowing your labels do not have the correct information on them. There is so much more I need to learn about this afs. Thanks again for listening.


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 Post subject: Re: arc flash study
PostPosted: Fri Apr 03, 2015 5:06 am 
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bure961 wrote:
Thank you for the great reply .
My concern is after so many years after the study there is no movement towards pm'img equipment. This timing issue could mean our ppe is not at the right level for protection against a fault? YES/NO? If the timing is off and the cb stays open longer than it should , are we not in trouble ?
We mention this to the company and the answer has always been about the PM cost of getting the work done. "we can t afford it now".
We are looking for ways to push the company into getting this done. It just doesn t seem right to do a study knowing your labels do not have the correct information on them. There is so much more I need to learn about this afs. Thanks again for listening.


The issue of PM's should have been listed in the report. At the very least, your PPE may be inadequate as it is probably based on the breaker closest to the fault operating. It may not and if a properly coordinated system, the next upstream device would trip. But in your case maybe not.

If the breaker sees a fault and has not had any PM or even exercising the breaker by opening and closing it periodically, it will take longer to open. The time used in the study to determine the incident energy is based on a properly functioning breaker. Longer time to open means a higher incident energy.

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 Post subject: Re: arc flash study
PostPosted: Fri Apr 03, 2015 4:37 pm 

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WBD your reply is very near to my thinking about ie and circuit breaker opening time which could cause ie being higher than listed on the label. With the 2015 nfpa listing the condition of maintenance as part of the safety program this seems to lean towards having the electrical equipment in good working order before an af study is done.

I believe 70e mention about conditions of maintenance in the 2012 edition of nfpa 70e ,don't know how far back this was mention in 70e.
Does anyone think that QW or electricians research the study before interacting with equipment ? Most would go by labels. Most don't have access to the report.

Thank you for giving your reply to my post very informing.


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 Post subject: Re: arc flash study
PostPosted: Sat Apr 04, 2015 4:51 am 
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Improper or inadequate maintenance is a FPN in NFPA 70E-2009 Article 130.3 which is the first time it appears.

I don't think any electricians research the report prior to working on the equipment. The labels are supposed to provide the information needed for the proper PPE.

I know of one facility where it was very evident that they had not done maintenance on the equipment and in the report the immediate upstream device, that would normally be the clearing device, was ignored. The next upstream device was assumed to operate. This lead to a vast majority of the equipment being >25 cal/cm2.

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 Post subject: Re: arc flash study
PostPosted: Mon Apr 06, 2015 9:36 am 
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bure961 wrote:
This timing issue could mean our ppe is not at the right level for protection against a fault? YES/NO?


It depends. This s not a black-and-white issue, and there are two directions to consider. First, failure to properly maintain equipment results in an increase in the likelihood of occurrence of an arc flash. In itself this is a bigger problem in my estimation because it's a relatively rare event in the first place and we'd like it to stay that way.

Case in point at a site that didn't do proper maintenance. Operators having trouble with a pump. Breaker (not overload) was tripping. After several attempts at resetting the molded case breaker in a 480 V MCC with no success, they called an electrician. Electrician arrives and does the exact same thing. Never mind the huge OSHA violation here. Eventually electrician gets out a meter and recognizes that motor is dead shorted to ground. Locks come out and motor gets replaced. Up to this point nobody had bothered to inspect the breaker as required by NEMA AB-4 and it was not inspected until after the incident. When electrician went to remove locks and close breaker in one last time to test equipment, breaker exploded and electrician was badly injured from arc flash. Oh, and the upstream breaker did work but at that time they didn't wear arc resistant PPE.

What happened here is a classic case of both improper mainteannce being done and no mainteannce being done at all up to this point. As I said, it increased the likelihood dramatically. The operator is just lucky that the electrician happened to be there when the breaker finally failed and not during all the attempts to close into a fault that were done up to that point.

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If the timing is off and the cb stays open longer than it should , are we not in trouble ?


Considering the increased hazard, fuses are basically electrochemical devices are are almost unaffected by age. They might trip sooner than expected but fuses that take longer than predicted to trip are very rare. All equipment in which the arc flash study got to the cutoff (usually 2 seconds) without tripping is also unaffected by equipment failures because there is no assumption that it will ever trip. Third, some equipment is just plain so low in terms of arc power that it never gets to the low level limit such as 1.2 cal/cm^2. So with respect to that equipment the incident energy study is still valid, even if the likelihood has dramatically increased and the breakers are all basically seized up scrap metal.

So I would have to answer the question with a qualified yes.

Quote:
We mention this to the company and the answer has always been about the PM cost of getting the work done. "we can t afford it now".
We are looking for ways to push the company into getting this done. It just doesn t seem right to do a study knowing your labels do not have the correct information on them. There is so much more I need to learn about this afs. Thanks again for listening.


Baby steps here. First, what about a simple IR scan? This is cheap and addresses one of the major causes of failures (loose connections) and the best part is that you don't even have to de-energize to do it, unless you made the mistake of "booby trapping" your medium voltage gear with door-trip switches so you can't open it while energized.

Second, did you actually generate a list of critical equipment yet that requires more than ""minimal" PM's? This would be:
1. Anything that production actually thinks is critical to life, health, etc. Think fire pumps and life support equipment.
2. Any breakers over 600 A frame sizes, especially molded case. Why? IEEE 493 documents that the failure rates on these are about 3 times higher than the smaller sizes.
3. Any breakers where failure would result in arc flash being higher than predicted. This usually means that for instance with an MCC, the "main" breaker needs to be PM'd but not the smaller ones, and 120/240 V lighting panels don't need an extensive PM either.
4. If you have electromechanical or solid state (not microprocessor) relays, at a minimum, pull the bucket out every 3 years and do the recommended time-current testing. Usually I only test 1 or 2 points on each function as a check and that's it. Reinsert the relay.

This means that all the little 15/20 A lighting panel breakers aren't touched unless they are on the critical list.

Mechanical issues (mostly lubrication) are the #1 cause of breaker issues. The #2 cause is problems with the trip electronics. If you can hit these two issues, you covered the vast majority of problems.

I would explain it like this with a standard list of questions:
1. Do you change your oil in your car/truck/SUV on a regular basis?
2. Do you check your air pressure and tire wear on a regular basis?
3. Do you check the pressure in your air conditioner on a regular basis?

Typically we all do #1 because we don't get very far without doing it. Fewer people do #2 but recognize the benefit (better gas mileage and fewer major expenses). Almost nobody does #3...we operate the air conditioner run-to-failure because it's a comfort/convenience item, even in the Southeast U.S. where I live.

With circuit breakers, exercising them and doing relubrication (changing the grease) is directly equivalent to #1. Doing the relay checking is equivalent to #2. And doing Doing that level of maintenance on a 15/20 A breaker in a lighting panel for the offices is equivalent to #3.

For some reason most people understand cars better than they do circuit breakers. But most people have dozens of circuit breakers in their houses and some don't even own a car. It's another one of those strange mysteries that we can't explain.


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