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PostPosted: Thu Oct 01, 2009 4:43 pm 
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Canuck01 wrote:
Situation: I need to test a 138/13.8 KV transformer secondary with an incident energy level of 58 cal. The breaker is racked out remotely using the CBS ArcSafe device, grounds are in on the 138 KV primary. How do I prove the secondary is de-energised to satisfy NFPA or CSA?


Again, I don't have a good answer for that, you already seem to have a mitigtion plan for this one but until then, don't know what to tell you. This has been a hot topic for a while now. My thoughts are if you have isolated the system you can wear your 40 cal suit and do your voltage test, but this needs to get clarified in the 70E for sure.

Canuck01 wrote:
Same situation 600 volt MCC main breaker with an incident energy level of 145 cal. How do I test that?



145 cal on a 600V MCC??? that seems a little excessive, what is your assumed clearing time?

Let me guess, no INST trips on the breaker feeding the MCC? Easy fix via breaker retrofit, use a arc flash reduction switch and tada, you should be <8cal/cm2


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PostPosted: Thu Oct 01, 2009 5:04 pm 
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Zog wrote:
Again, I don't have a good answer for that, you already seem to have a mitigtion plan for this one but until then, don't know what to tell you. This has been a hot topic for a while now. My thoughts are if you have isolated the system you can wear your 40 cal suit and do your voltage test, but this needs to get clarified in the 70E for sure.



145 cal on a 600V MCC??? that seems a little excessive, what is your assumed clearing time?

Let me guess, no INST trips on the breaker feeding the MCC? Easy fix via breaker retrofit, use a arc flash reduction switch and tada, you should be <8cal/cm2


FCT is over 2 seconds. Most of the issue is 1700 feet cable length and instantaneous set to 20X upstream. Absolutely a candidate for an arc flash relay. We have Vamp in some MCC's but they don't do much for me (distrustful of their technology, kind of like an air bag phobia. Will it go off?). I like Schweitzer 751A - clears in 4 to 6 ms. Add 50 ms for the breaker to clear and you get down to less than 8 cal. I'm not sure how I'll manage the "test" portion but due diligence and a 40 cal suit could be sufficient. I wish hazards above 40 cal were addressed better by NFPA and CSA. We really get hung out to dry trying to deal with the higher hazards. Maybe somebody should invent a remote control testing :) vehicle. Hotstick mounted on a toy monster truck maybe??


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PostPosted: Thu Oct 01, 2009 8:08 pm 
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Maybe someone is already working on that :)


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PostPosted: Fri Oct 02, 2009 7:32 am 
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Canuck01 wrote:
I wish hazards above 40 cal were addressed better by NFPA and CSA. We really get hung out to dry trying to deal with the higher hazards.


Actually, there is NO discussion of anything above 40 cal/cm2 in the NFPA 70E. The only mention is in 130.7(A) FPN No. 2, which says,

"When incident energy exceeds 40 cal/cm2 at the working distance, greater emphasis may be necessary with respect to de-energizing before working within the Limited Approach Boundary of the exposed electrical conductors or circuit parts."

Note, this is a FPN, which according to NFPA guidelines, is unenforceable. It also suggests that "greater emphasis may be necessary," essentially leaving it up to the employer to determine if it is ok to work.

Just because the Hazard/Risk Categories do not address anything above 40 cal, does NOT mean that 70E forbids work above those levels. This should be a company decision. If you must test for voltage inside the boundary, and the arc flash rating is over 40 cal, I would suggest suiting up to the maximum that you can. You can buy 100 cal suits if that is what is necessary. And yes, take all the additional precautions you can to ensure you don't slip up. But it CAN be done, and IS permissible.


I will stop ranting. I am just tired of engineers, who should be used to reading standards, citing a NON-EXISTENT requirement to stop all work above 40 cal/cm2.

Canuck, I just noticed that you are in Canada. (That should have been obvious from the name...) I don't know what the CSA standard says about this.
But the rant still holds for those in the US.


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PostPosted: Fri Oct 02, 2009 7:55 am 
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Wdean, I agree with your entire post but the OP's Ei is 145 cal/cm2, no suits exist for those levels that I am aware of.


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PostPosted: Fri Oct 02, 2009 8:47 am 
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I will suggest that, unless it is armoured, probably wouldn't provide the needed protection anyway.


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PostPosted: Fri Oct 02, 2009 8:56 am 
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Zog wrote:
Wdean, I agree with your entire post but the OP's Ei is 145 cal/cm2, no suits exist for those levels that I am aware of.


:o
Ok, clearly at 145 cal, something needs to be done, and done quickly!
There is no way you could get me close to something like that if I thought it could be energized!

Just for the record:
I am not saying that anyone SHOULD work when the calculations show over 40 cal/cm. I am simply stating that it is not against codes to do so. Any decision to do so should be made at the company / site level.


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PostPosted: Fri Oct 02, 2009 9:49 am 
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The real problem here is we need a way to define incident energy per unit time which presently does not exist (at least in any standard). My guess is you have a low energy per time, just lots of time. In the future if we have the energy per time method, we would be able to say you have a lot of total energy but low energy per time so it is not an explosion. Then the question becomes, will the low fault even sustain long enough to be a problem.

Does the 2 second cut off get you any where? That's the other problem. We are still trying to figure out if low fault currents (which I assume you have) can even sustain very long.

For now, there is not a good technical answer from the standards side of things except to try the 2 second rule. I agree with WDeanN that the 40 cal limit gets overplayed. 40 cal over a few cycles is serious, 40 cycles over several seconds is probably not as serious.

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PostPosted: Fri Oct 02, 2009 11:09 am 
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I've been told that the high incident energy, long duration faults have substantially lower blast hazards. While I think a +100 cal incident energy level is hazardous, the reduction in blast energy is something of a saving grace. CSA is quite clear in acknowledging they basically copied the NFPA standard. I've never found anything in Z462 directly referencing safe work practices above the 40 Cal level. I assume this is because the blast effect above 40 cal is probably lethal - where the cut-off point is for the drop in blast energy lethality is not something I know. This is why I'm struggling so badly with the higher incident energy levels...
Immediate changes to the protection schemes is something I can and will do but I am left with a few areas that I can't fix until I can schedule an extended down period. The worst of it is telling my crews how to work safely when Z462 isn't clear on +40 cal hazards other than directing you to avoid contact and engineer a solution. There is a period of time when you need to manage the hazard. My consistent direction to my crews has been switch upstream. There is no hazard we can't manage without a little communication. In fact, withdrawing underground personnel to deal with an electrical hazard is something I've already done. At least my crews are on-board with Arc Flash!
FYI: CSA Z462-08 is still a standard at this point. We are not legislated to follow Z462 but it would be uncomfortable to be in front of the judge knowing Bill C-45 would be used ("217.1 Every one who undertakes, or has the authority, to direct how another person does work or performs a task is under a legal duty to take reasonable steps to prevent bodily harm to that person, or any other person, arising from that work or task."). There is a reference in the CEC directing Canadian operations to follow NFPA 70E so we really do need to follow the rules or pay the consequences through the courts.


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PostPosted: Fri Oct 02, 2009 8:42 pm 
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Can you put a tictracer on a shotgun or insulated pole. Would 6 or 8 ft drop you down to 40cals?


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PostPosted: Sat Oct 03, 2009 7:43 am 
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Proximity voltage detectors and Arc Flash Clothing

It could. If the calculated energy was at 15-18 inches and the energy was in the 100's this is pretty reasonable. The issue is a matter of calculation.

Most of the software calculators allow you to enter worker distance and calculate based on worker distance. Tic tracers aren't approved determining absence of voltage but could be used for troubleshooting. On medium voltage, the NESC or 1910.269 would usually be interpreted to allow you to use a proximity tester if it is tested before and after use to determine it is working properly. You would then ground the line (also from the hotstick) and begin work. NFPA 70E really required an "approved voltage detector" so it has to detect 0 volts. Most proximity devices are incapable of doing this.

We support distance the critical factor even with distance is knowing the energy level you are working with (which is still uncommon) and knowing the limitations and failure modes of your testing device.


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PostPosted: Sat Oct 03, 2009 8:13 am 
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Canuck01 wrote:
FYI: CSA Z462-08 is still a standard at this point. We are not legislated to follow Z462 but it would be uncomfortable to be in front of the judge knowing Bill C-45 would be used ("217.1 Every one who undertakes, or has the authority, to direct how another person does work or performs a task is under a legal duty to take reasonable steps to prevent bodily harm to that person, or any other person, arising from that work or task.").


You probably have provincial legislation about that same concept.

Canuck01 wrote:
There is a reference in the CEC directing Canadian operations to follow NFPA 70E so we really do need to follow the rules or pay the consequences through the courts.


The 2009 edition of the CEC points to CSA Z462 instead. Don't know if Saskatchewan intends to use it (Ontario skipped the 2006 edition but has already adopted the 2009 edition).


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PostPosted: Sat Oct 03, 2009 8:24 am 
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elihuiv wrote:
It could. If the calculated energy was at 15-18 inches and the energy was in the 100's this is pretty reasonable. The issue is a matter of calculation.

Most of the software calculators allow you to enter worker distance and calculate based on worker distance. Tic tracers aren't approved determining absence of voltage but could be used for troubleshooting. On medium voltage, the NESC or 1910.269 would usually be interpreted to allow you to use a proximity tester if it is tested before and after use to determine it is working properly. You would then ground the line (also from the hotstick) and begin work. NFPA 70E really required an "approved voltage detector" so it has to detect 0 volts. Most proximity devices are incapable of doing this.

We support distance the critical factor even with distance is knowing the energy level you are working with (which is still uncommon) and knowing the limitations and failure modes of your testing device.


Thanks for that excellent observation! The working distance calculation was based on 18" working distance if I recall correctly. Another calculation based on 6' "testing" distance would probably knock the incident energy level down to a tolerable level. Does anyone know of any precedent for taking this approach? It would be breaking new ground in CSA Z462-08. With regards to our MV testing procedure - after isolation, we use a Salisbury voltage tester then flash the buss with a CATU grounding cable set up on a hotstick - all testing is done in PPE to the calculated level or 40 cal gear. I do take issue with Salisbury's testing procedure in that there is no reason to set the detector to the 4.2 KV setting when testing at 4160 because you need to go down to the 240 volt level regardless for detector verification. Why work your way down when a positive test will result at the 240 volt setting. I see value switching through the ranges at the higher voltages to avoid spurious voltage indications.


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PostPosted: Mon Oct 05, 2009 8:25 am 
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Canuck01 wrote:
Thanks for that excellent observation! The working distance calculation was based on 18" working distance if I recall correctly. Another calculation based on 6' "testing" distance would probably knock the incident energy level down to a tolerable level. Does anyone know of any precedent for taking this approach?


As a general rule of thumb, for medium voltage, due to the squared relationship with distance, if you double the distance, you will half the energy.

For low voltage, it is a little bit more complicated, but in general, for switchgear, if you double the distance, you can drop the energy level by about 1/3. So that for a 100 cal/cm switchgear at 18", if you back up to 3 feet, you could be in the range of 33 cal/cm.

These are just general values, and analysis should be done on your system to verify this.


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PostPosted: Tue Oct 06, 2009 6:57 am 
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Increased working distance

I had the ETAP model tweaked with longer working distances and was pleasantly surprised to find a major reduction in incident energy levels. Does anyone know of any precedent for increasing the working distance to 4' for testing purposes per section 4.2 of Z-462, section 120 of NFPA 70E?


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PostPosted: Wed Oct 07, 2009 8:22 am 
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Canuck01 wrote:
Situation: I need to test a 138/13.8 KV transformer secondary with an incident energy level of 58 cal. The breaker is racked out remotely using the CBS ArcSafe device, grounds are in on the 138 KV primary. How do I prove the secondary is de-energised to satisfy NFPA or CSA?
Same situation 600 volt MCC main breaker with an incident energy level of 145 cal. How do I test that?

I must test to prove the circuit is de-energised but it is impossible to do it safely?
I can't always shut it off upstream to reduce to cal levels because we're a mine and people are 3000 feet underground, the mill is running and would plug up imediately...


I've been dealing with similar issues on the low voltage side and our solution is to clear the upstream feeder. In your description, you state that the 138KV primary switch is cleared and grounded, so the only source of power is a backfeed. You can then recalculate the backfeed IE (if any) and then suit up accordingly. If there is no alternate source of energy, and the primary is fully locked out and grounded, why do you need to test for voltage at all? Personally I would use a tic tracer and grounding straps for safety, but the source of energy is removed and you're only worried about capacitive charges at this point. Same thing on low voltage - clear the primary and lock it out, then the secondary main is safe to test and work on. Am I missing something here?

TxEngr


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PostPosted: Wed Oct 07, 2009 9:48 am 
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TxEngr wrote:
I've been dealing with similar issues on the low voltage side and our solution is to clear the upstream feeder. In your description, you state that the 138KV primary switch is cleared and grounded, so the only source of power is a backfeed. You can then recalculate the backfeed IE (if any) and then suit up accordingly. If there is no alternate source of energy, and the primary is fully locked out and grounded, why do you need to test for voltage at all? Personally I would use a tic tracer and grounding straps for safety, but the source of energy is removed and you're only worried about capacitive charges at this point. Same thing on low voltage - clear the primary and lock it out, then the secondary main is safe to test and work on. Am I missing something here?

TxEngr


Sounds pretty good other than reconciling the Incident energy levels. You can clear upstream and still need to test downstream. What level will you suit up to and still comply with the regulations? If the energised hazard is 40 cal, would it follow that the de-energised hazard could be 40 cal until tested?

Our 138 KV incomer is an anomoly only because of the grounding capability. Normally I'm trying to deal with the typical distribution system. I get stuck at the final test at the point of electrical work. It seems like you need to dress to the label until verified de-energised even though you may have opened the circuit upstream and verified upstream.


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