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PostPosted: Thu Feb 26, 2009 8:49 pm 
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Zog wrote:
You said the gear should contain the blast, which it probally wont. As far as racking breakers go, thats what remote racking is for. http://www.remoterackingsolutions.com


ZOG, have you ever tried using one of the commercially available remote racking devices? We have, multiple times including two separate days with the factory representatives on hand. Always unsuccessfully.

The device that we used was industry recommended and included tork sensing (for safety purposes). The tork program was not right the first day and after about six trys (on de-energized switchgear) we quit. About a week later with a new program installed that was supposed to be corrected for the brand of switchgear, it still failed.

Watching this happen, knowing that for two differnet breaker models we needed two different tork programs, and imagining the risk of mistorking a breaker into energized switchgear because of some robotic device, it was an EASY DETERMINATION that racking breakers in manually may still be the safest. An arc flash is horrible to consider while a worker is racking the breaker in manually, but it also seemed risky that the remote racking device might cause an arc flash. Avoidance is preferred to withstand. I am certain there are locations that have successfully used these devices, but we did not have enough time to work it out and as mentioned, it seemed safer to the informed observers to use the manual method.


Similarly there exist very real concerns with applying arc resistant switchgear. For example this is a liability to put within a purged substation located within a classified hazardous area. Or if the site conditions do not provide a good 'chimney' for the arc blast.

There HAS been research completed on non arc resistant gear regarding venting of arc flash pressures while maintaining cubicle integrety. This should be a manufacture's responsability. It is not unreasonable to expect manufacturer's of gear with a specified AIC rating to assure the doors will not blow off at such fault levels, even if as you keep saying, that was not what the gear was designed to contain. That would be akin to including good brakes on a car specified with high horsepower.

There is more to this than simple answers.


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PostPosted: Fri Feb 27, 2009 6:49 am 
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Gary B wrote:
ZOG, have you ever tried using one of the commercially available remote racking devices? We have, multiple times including two separate days with the factory representatives on hand. Always unsuccessfully.


Gary B wrote:
Similarly there exist very real concerns with applying arc resistant switchgear. For example this is a liability to put within a purged substation located within a classified hazardous area. Or if the site conditions do not provide a good 'chimney' for the arc blast.


yep, those are real concerns, again, new technology with better solutions being developed.

Gary B wrote:
There HAS been research completed on non arc resistant gear regarding venting of arc flash pressures while maintaining cubicle integrety.


I have witnessed some of this testing in person, each arc is different and the same test set up produces different results each time.

Gary B wrote:
It is not unreasonable to expect manufacturer's of gear with a specified AIC rating to assure the doors will not blow off at such fault levels, even if as you keep saying, that was not what the gear was designed to contain.


I agree, however, you cant count on it so PPE should still be worn.


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PostPosted: Sat Feb 28, 2009 8:02 pm 
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Location: Calgary, Alberta, Canada
I am 100% behind Gary B, for all the reasons he provided. As well we have to be careful how we implement 70E and Z462.

The electrical distribution equipment is manufacturered to applicable Standards, and installed to the NEC or CEC by a qualified, competent electrician working for a licensed contractor.

Safe installations must be assumed before we energize the electrical equipment. Once it is energized the equipment operate safely with a low probability of abnormal failure while in operation unless we operate the equipment outside of its limits, and don't complete maintenance.

We MUST assume the equipment will operate safely with a very low probability of failure during normal operations. Normal means that we can switch a breaker of fused disconnect with the load turned off and the probability of abnormal failure is very low.

If we don't do this we will have a problem running the refineries, factories, etc... where we require operations staff to turn things off during normal operation and apply a lock, there is not enough electricians to go around.

Operators can only open or close breakers and switches, following an approved procedure, with training and cannot reset tripped breakers or replace blown fuses.

We have to ensure we implement 70E and Z462 practices from a practical and appropriate perspective, with a risk analysis that makes sense.

Regards;
Terry Becker, P.Eng.
http://www.esps.ca


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PostPosted: Sun Mar 01, 2009 7:38 am 
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Terry Becker wrote:
Safe installations must be assumed before we energize the electrical equipment.

We MUST assume the equipment will operate safely with a very low probability of failure during normal operations. Normal means that we can switch a breaker of fused disconnect with the load turned off and the probability of abnormal failure is very low.


I dont know about you but in my experience I have seen way to many failures occur when energizing new installations to ever make any assumptions . The 70E tables would agree with me.

Terry Becker wrote:
If we don't do this we will have a problem running the refineries, factories, etc... where we require operations staff to turn things off during normal operation and apply a lock, there is not enough electricians to go around.


This.....
Terry Becker wrote:
and cannot reset tripped breakers or replace blown fuses.


Contridicts this. You are misunderstanding this requirement:

"(1910.334)(b)(2) "Reclosing circuits after protective device operation." After a circuit is deenergized by a circuit protective device, the circuit protective device, the circuit may not be manually reenergized until it has been determined that the equipment and circuit can be safely energized. The repetitive manual reclosing of circuit breakers or reenergizing circuits through replaced fuses is prohibited.

Note: When it can be determined from the design of the circuit and the overcurrent devices involved that the automatic operation of a device was caused by an overload rather than a fault condition, no examination of the circuit or connected equipment is needed before the circuit is reenergized."

A qualified person that understands the construction and operation of the equipment and system they are working should know how to determine either the cause of the breaker trip or determione if the system is safe to re-energize.


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PostPosted: Fri Apr 09, 2010 7:16 am 
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Joined: Fri Jul 10, 2009 8:57 am
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Location: Toronto
Moulded /molded case breaker operation

I'm grappling with this too. We have quite a few 208 V distribution panels that are fuse protected and even with the 2-second cap have quite high incident energy (Cat 3 and 4 at 18"-- and yes, I have no qualms about calling these energy categories, I don't care that the original intention of this was to include risk... more on risk below...) , but I'm going to have a miserable time getting guys to don a face shield never mind a flash suit just to turn off a heater.

So we've done the calculations, and if it goes, it will be bad. No argument there.

In talking to stations staff, I can't find anyone who has heard of a moulded case panel breaker failing while trying to operate it. They've seen tabs break off, but that it intself never caused an arc. People have caused arcs by sticking a screwdriver in where the tab was (duh).

What is people's experience with moulded case breakers? Is it reasonable to say that the probability of catastrophic failure is so low that forcing people into high energy PPE to flip a breaker is a bit ridiculous?

Jody Levine
Hydro One
Station Maintenance Technical Services


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PostPosted: Wed Apr 28, 2010 5:05 pm 
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It seems like the question is whether to gear up to the full hazard for every task or to consider risk.

I won't pretend to have the answer, but one large Utility in my area uses a hazard-risk matrix to decrement the labeled HRC. So for operations like you describe, where the potential IE is high but the risk is very low, they decrement the HRC by two catagories.


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PostPosted: Sun Apr 10, 2011 3:54 pm 
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arcflash71 wrote:
It seems like the question is whether to gear up to the full hazard for every task or to consider risk.

I won't pretend to have the answer, but one large Utility in my area uses a hazard-risk matrix to decrement the labeled HRC. So for operations like you describe, where the potential IE is high but the risk is very low, they decrement the HRC by two catagories.


Our paper mill companies do the same thing. We have a documented risk assessment in our eswp where we assessed various work tasks and provide a caloric reduction (in lieu of a category reduction) to arrive at the required level of PPE for each task.

I would be interested to know the uitlity that you are referring to. When we adopted this approach in 2010 we thought we were the only ones in the world who would consider such a thing.


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PostPosted: Mon Apr 11, 2011 5:53 am 
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I worked at several utilities and none of them reduce the level of the documented HRC. Some of these facilities are old and even though they receive regular maintenance and inspection, it would be hard to predict how and old circuit breaker will respond when subjected to fault currents. The stresses introduced during the inspection and testing is far below those that occur during fault. I have seen too many pieces of equipment fail after passing all their tests, all results well within specs. The only true test is energization and even that won't tell you what will happen during a faullt.


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