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 Post subject: "Dead" Equipment after Tested or Tested AND Grounded
PostPosted: Mon Sep 15, 2014 3:04 pm 

Joined: Mon Dec 15, 2008 12:36 pm
Posts: 4
Hello,

I am working on arc flash studies for high voltage substations (mostly 115kV) and have run into a question. When a worker is going to de-energize a system to work on it, he switches, tests "dead," and then hangs grounds. When is the system considered to be "dead" from an arc flash hazard perspective? That is, we currently have incident energy results for the switching (at a certain distance), but when hanging grounds, the worker has to get much closer to the bus. Do we need to consider the bus energized and have workers suit up appropriately to hang the grounds, or is it ok to hang the grounds without suiting up for the full arc flash hazard once the system has been switched and tested "dead?" Is this where we use the "risk" part of the hazard/risk analysis and say that once it's tested, the risk is low, and therefore the worker doesn't need to suit for the full energized hazard? I'm curious what others have done or seen done.

Thanks for any input!
Deborah


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 Post subject: Re: "Dead" Equipment after Tested or Tested AND Grounded
PostPosted: Tue Sep 16, 2014 6:37 am 
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Joined: Wed May 07, 2008 5:00 pm
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Location: Rutland, VT
Hi Deborah,

Per the newly released NFPA 70E-2015, Table 130.7(C)(15)(A)(a), contains a line item that states application of temporary protective grounding equipment after voltage test requires PPE.

All that being said, you are a utility so NFPA 70E does not apply plus your practices are different where a visible break is required which is not the case for other industries. The new OSHA 1910.269 Appendix E contains a section on Probability that an electric arc will occur which is part of the assessment guidelines to determine PPE requirements. Perhaps your safety department could take that into account in making this determination. For example: a visible break plus testing plus short time between testing and installing grounds = low risk for arc flash and reduced PPE can be used.

It will be interesting to see responses from others here that are utilities.

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Barry Donovan, P.E.
www.workplacesafetysolutions.com


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 Post subject: Re: "Dead" Equipment after Tested or Tested AND Grounded
PostPosted: Wed Sep 17, 2014 12:08 pm 
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Location: North Carolina
Keep in mind with utility work, there are three classes of hazards to be concerned with when grounding. The first are voltages that are applied to a line while diconnected. This would be lightning, customers with improperly wired generators, and accidents (dropping an energized line onto a de-energized one). With these hazards after checking for absence of voltage, the likelihood of a hazard would indeed be small based on a narrow time window.

The second group of hazards would be latent potential voltages. These are not detectable using purely noncontact meters. This would include capacitors and the capacitance built up within shielded cable in underground utilities. It can even be a static charge such as that created by wind blowing across the lines in a dry arid environment. Once grounding is applied, these are all neutralized and after that point, the grounding is not doing anything.

The third group of hazards are induced voltages. These occur by inductance from nearby lines, or by triboelectricity such as wind blowing on a line on a dry day. These voltages appear continuously and the only way to control them is via a low impedance circuit such as a SINGLE POINT work site ground (equipotential grounding).. Inserting a ground typically involves very little arcing but you are nearly gauranteed to get some sparking/arcing when removing a ground where induced voltages are present.

NESC (among others) says that PPE must be worn. It is certainly possible to calculate the size of the induced voltages and thus require substantially reduced PPE for the activity of applying and removing grounds in many cases even though all the values are generally somewhat random voltages. Although this is the case, there is plenty of guidance on this subject so it should be no mystery as to the size/scope of the problem.


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 Post subject: Re: "Dead" Equipment after Tested or Tested AND Grounded
PostPosted: Mon Sep 22, 2014 9:15 am 
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Joined: Tue Jan 13, 2009 5:00 pm
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What's the down side of using PPE while applying grounds? You already have someone suited up for testing. Can't this same individual proceed to apply the grounds before removing the PPE? Is safety compromised by wearing PPE for this task?

Risk= impact*probability. I agree the probability is low following isolation and testing, but it is not zero. The impact remains very high, so risk is...?


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 Post subject: Re: "Dead" Equipment after Tested or Tested AND Grounded
PostPosted: Mon Sep 22, 2014 12:02 pm 
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Location: Rutland, VT
stevenal wrote:
What's the down side of using PPE while applying grounds? You already have someone suited up for testing. Can't this same individual proceed to apply the grounds before removing the PPE? Is safety compromised by wearing PPE for this task?


I am hoping the OP will provide insight on this but from my experience it could be that the testing is done by an individual on the ground with the tester on a long extendo stick. The grounds may be applied by a different individual from a bucket truck since the handles on the ground sticks are shorter than the extendo stick. Therefore, the individual applying the grounds may have to be suited to a higher level of PPE than the person on the ground testing "dead".


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 Post subject: Re: "Dead" Equipment after Tested or Tested AND Grounded
PostPosted: Mon Sep 22, 2014 8:20 pm 
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A hot stick is a hot stick. Minimum length is determined by voltage as per IEE 516. You can go longer but at some point the stick weight and lack of dexterity give way. Usually a voltage detector is mounted on a universal spline fitting. Grounds are usually attached with a shotgun stick because its easier than using a hook and crankiing with a hook stick head. The alternative of course is that since 115 kv is well above glove work limits, use bare hands techniques at which point grounding the line is unnecessary. Shotgun sticks can be operated with a rope so length becomes a nonissue.

Also pay attention to NESC tables. If you are already locking out reclosers and such, might as well set trip settings so that they allow for minimum PPE. At 115 kV the biggest limitation is slow SF6 breakers dominating trip times.

Telescoping sticks are helpful for storage only. They are much heavier than fixed sticks.


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