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 Post subject: Terminating in >1kV Metal Clad Switchgear
PostPosted: Tue Feb 23, 2016 2:52 am 

Joined: Tue Feb 23, 2016 2:39 am
Posts: 2
Hi All, First post.
I am trying to assist with a risk assesment for the termination of cables into old 11kV metal clad switchgear.
The board has a very high fault energy and approach boundary, something like CAT 4, 30m flash hazard boundary.

The job is to remove old cables and terminate new cables into the cable zone. The Breaker will be withdrawn and the earth switch applied, tested for dead before the permit to work will be issued. Cable termination onto dead palms is considered low risk work.

On previous projects no additional PPE above level 0 has been required (so long as no switching is taking place) to work within earthed sections of the board or the LV control cubicle. Is this how others interpret AF standards.


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 Post subject: Re: Terminating in >1kV Metal Clad Switchgear
PostPosted: Tue Feb 23, 2016 5:35 am 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 820
Location: Rutland, VT
AR PPE is needed when there is a risk of an arc flash event. This would include testing for de-energized. Once it has been confirmed that the equipment is de-energized the risk of an arc flash event has been removed, therefore AR PPE is no longer needed.

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 Post subject: Re: Terminating in >1kV Metal Clad Switchgear
PostPosted: Tue Feb 23, 2016 7:08 am 
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Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
To follow up on this...

In the past 2 or 3 years at one particular site there were multiple instances where individuals either purposely or accidentally applied grounds first before applying a voltage detector on what were believed to be de-energized and locked out circuits. The result in all but one of the cases was a near miss but in the last case, there were other circumstances that resulted in a severe arc flash and that individual has been out of work for almost a year now. And this is with cabling and true temporary personal protective grounds. Several Canadian mines and several U.S. petrochemical sites I'm familiar with have reported multiple instances with ground trucks ("Earthing switches") that they put in the cell after removing the breaker where the truck flashed over and was severely damaged for various reasons mostly related to things not being as expected. Either way the approach of making grounding the first step and testing the second step pretty much turns the grounding itself into a "testing" method...if it doesn't flash, there wasn't any hazardous voltage!

The alternative which is espoused by other codes and regulations is to perform the test for absence of voltage first followed by application of grounding. If the test device is a capacitive meter then it will not detect voltage so long as any inductively or capacitively coupled voltages are minimal. Cases where this test would fail for instance are when testing on the load side of a vaccuum interruptor when there is little or no load present, or when testing a single circuit with two parallel overhead lines where voltage is inductively coupled onto the second line. Capacitive charges either induced by static charge (wind) or from residual stored charge in shields or from actual capacitors will not be detected. With a resistive-type meter though all of these charges would be detected, so a test for "absence" of voltage may lead to an invalid conclusion, indicating voltage is present when in fact the only issue in reality is grounding has not been applied yet which would remove all of these hazardous voltages.

Personally I'm at a bit of a loss here as to what the best approach is. I certainly don't want to encourage the intentional creation of an arc flash caused by failures to identify the correct circuit. And personally I can't even blame the work crews for this because I have very close and personal experience with locking out the wrong circuit and "discovering" it for myself. One can argue for good drawings, documentation, labels, etc., forever but the fact remains that there will always be circumstances where it is not 100% clear what components are energized and which are not...hence the test for absence of voltage. Furthermore the issue remains as to whether it is better to ground first and be 100% assured that barring any other problems that the test for absence of voltage always succeeds, or whether it is better to test first and potentially have a discrepancy that has to be resolved before grounding. And one could argue for a second test for absence of voltage even after that just to ensure that mistakes weren't made in the grounding procedure.

So...I don't know if I'm just raising awareness here or looking for a reasonable alternative because similar to the arguments for/against single point "worksite" grounding, there are clear and obvious arguments for both approaches and I have yet to see a clear winner either way but I also don't want to see my friends or myself injured or killed and given that the hierarchy of controls says that PPE is the last resort, I'd like to see a better alternative.


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 Post subject: Re: Terminating in >1kV Metal Clad Switchgear
PostPosted: Tue Feb 23, 2016 10:58 pm 

Joined: Tue Feb 23, 2016 2:39 am
Posts: 2
Thanks for the responses guys.
I wrote out a longer version but I got logged out when I pressed submit and its all gone :(


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