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 Post subject: is it really de-energized?
PostPosted: Tue Oct 18, 2011 12:51 pm 
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Can anyone help me to answer this question? I got this in one of my arc flash hazard trainings and I couldn't answer it properly.

CSA Z462-08, section 4.2.1 elaborates how to set up electrically safe work condition, under item(e), it asked us to use an adequately rated voltage detector to test each phase conductor or circuit part to verify that they are de-energized........

What if the equipment was labelled as "danger" arc flash hazard, before you can make sure it is de-energized, what kind of PPE you should wear to do this work. From my understanding, if we are not 100% sure that equipment is de-energized, it is still under "danger" category and there is no PPE existed.

I believe that is sort of interacting with the equipment.

Thanks!


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PostPosted: Tue Oct 18, 2011 12:59 pm 
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I think the only solution in this situation, without system changes, is to de-energize and test somewhere upstream of the dangerous location, perhaps on the primary of a transformer. A better solution is to modify the system (add zone-selective interlocking, maintenance switches, etc.) to mitigate the dangerous condition.

As you noted, you cannot assume that the equipment is de-energized and use lower value PPE. If you could, you wouldn't have to do the voltage testing in the first place.


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PostPosted: Tue Oct 18, 2011 2:31 pm 
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Location: Charlotte, NC
First off that whole "No PPE can protect you" is debateable, nothing says you can't wear a 100cal/cm2 suit if the hazard is 80 cal/cm2. The 40 cal danger limit comes from a footnote in the 70E handbook back in 2004 if I recall. That said, I would not want to find out first hand if the blast pressure would be fatal or not.

Another thing to keep in mind is working distance, it makes a huge difference so if you use a meter on the end of a hot stick you can greatly reduce the Ei.


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PostPosted: Wed Oct 19, 2011 8:54 am 
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The note is in the 2009 Handbook as well, with additional info. In a few days I should receive the 2012 Handbook.

The handbook's note reads: "... If the arc flash hazard analysis indicates an exposure of more than 40 cal/cm^2, the task must not be performed until an electrically safe work condition exists. FR clothing with a very high incident energy rating might be needed to perform the steps necessary to establish an electrically safe work condition. However, this is the only task that should be accomplished with the equipment energized. ..."

The "must not be performed" part is not from the standard itself.

And the last part specifically allows (in the opinion of the handbook authors) the steps to establish an electrically safe work condition to be performed where IE > 40 cal/cm^2, of course with proper PPE.


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PostPosted: Wed Oct 19, 2011 9:03 am 
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Actually what I want to discuss is how to proceed verification step when the equipment is de-energized. Do you still wear PPE as indicated as "danger" level to do this test? Is it acceptable to test the upstream device only to ensure the downstream device is no longer live?

I can't image that electrician will have to wear heavy PPE to do the voltage test, do you see anything really happened?


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PostPosted: Wed Oct 19, 2011 11:22 am 
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Noah wrote:
Actually what I want to discuss is how to proceed verification step when the equipment is de-energized. Do you still wear PPE as indicated as "danger" level to do this test? Is it acceptable to test the upstream device only to ensure the downstream device is no longer live?

I can't image that electrician will have to wear heavy PPE to do the voltage test, do you see anything really happened?


I don't see why you couldn't test the upstream device if you have up-to-date diagrams or other evidence that the upstream device is the only source. You may argue that this is leaving a lot of room for error, but I don't see anyone arguing that a maintenance switch on an upstream device would be unacceptable to reduce the hazard. Seems to me that the same room for error would exist there.

As far as the possibility of anything really happening while testing the de-energized equipment goes, why would you have to test it if you were absolutely sure that it was de-energized?


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PostPosted: Thu Oct 20, 2011 6:23 pm 
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It is required by CSAZ462.


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PostPosted: Fri Oct 21, 2011 9:12 am 
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Noah wrote:
It is required by CSAZ462.


So is using proper PPE.


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PostPosted: Fri Oct 21, 2011 10:28 am 
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So it goes back to the original discussion, if that is "Danger", you still need to wear very heavy PPE to verify(test) the voltage even it is de-energized. I don't think it is practical way but is there an alternative instead of do anything on upstream?


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PostPosted: Wed Dec 07, 2011 10:36 am 

Joined: Sat Nov 20, 2010 10:17 am
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Location: Victoria British Columbia
When testing to ensure a circuit is de-energized you must wear the appropriate PPE as identifed in the hazzard analysis. The only way to to eliminte this requirement would be to use some form of local or remote metering to verify the circuit de-energizes when the CB is open; and then you would probably have to verify correct operation of the remote metering prior to issolating. Of course you could revert to upstream testing but then again PPE will be required for that as well.


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PostPosted: Mon Apr 09, 2012 7:51 am 
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Location: Calgary, Alberta, Canada
A risk assessment could be used. This is a unique case where the arc flash suit you purchased may not have the ATPV for the incident energy on the Danger label. Zog is correct above and unfortunately industry seems to think that 40 cal/cm2 is a cut off when it is not. Unfotunately the power engineering software and the engineers performing the incident energy analysis just let the software print out the Danger labels by default with no real understanding of CSA Z462. They also include HRCs on the labels which is not technical correct, but here again the software prints the HRC by default.

We need the software to be fixed, but I cannot get anyone at ETAP, SKM or Easypower to listen.

Back on topic, based on observing a visible disconnect from the utility fuses to the primary of the transformer and the utility installing Temporary Protective Grounds the probability of voltage still been present is 0%. Wear the arc flash suit you have e.g. 40, 55, 65 cal/cm2 and complete the voltage test in the Main Breaker.

Regards;
Terry Becker, P.Eng.
ESPS Electrical Safety Program Solutions INC.
See my LinkedIn Profile.


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PostPosted: Tue Apr 10, 2012 6:30 pm 
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Quote:
based on observing a visible disconnect from the utility fuses to the primary of the transformer and the utility installing Temporary Protective Grounds the probability of voltage still been present is 0%.


I 100% disagree.

This might work for instance if you have a portable tool where you can positively verify that there are simply no other voltage sources than the plug. In fact, it can work in any electrical equipment that cannot store energy in any way that meets what you described. This would be flat out wrong with medium voltage equipment where voltage repolarization in the insulation itself can harbor charges (thus the reason for grounding at least initially), and it cannot be trusted where inductive pickup is a potential hazard such as with long parallel lines. Unfortunately, the list of places where this applies is much shorter than those cases where it doesn't, and the time it takes to test before touch is so little that it's good practice even when it seems "silly".

About 7 years ago I was working with a young kid who by rights shouldn't have even been hired on as an electrician. Anyways, we had a problem with a 2400 V dry transformer and he was scared to even touch it (not a bad thing). There were two identical transformers in the switchgear room. So we opened the disconnect and locked it out. So far, so good. We then opened the cover. At this point because the layout was clean and obvious and we had 0% chance of a problem as you described. I even went so far as to open the 480 V fused disconnect downstream of it and test it there with a meter. Dead as can be. Next, we popped off the cover. I grabbed onto the taps and started wiggling them to check for any signs of looseness or corrosion. When I did that, suddenly it was like wrestling a live animal! Oops. Dug out a voltage detector and checked...sure enough, it was live as can be. After very carefully following the conduits (60 year old plant in this area, so conduit runs were not exactly straight runs), we figured out that everything crossed over each other and that the labels were all backwards. Not sure if the kid learned something that day or I did. I am just thankful that the tap didn't break loose and that I had dry leather gloves on so the surface voltage on the insulation didn't get me.

I've had 3 other incidents in the last 10 years where I went to troubleshoot something and checked for voltage first, and found that regardless of whether I thought I locked it out, it was still energized. None were as dramatic as that one because I practiced test-before-touch every time directly on the equipment.

Do not think of this step of the procedure as really accomplishing anything...all you are doing is one final verification step to make sure that indeed you're absolutely, positively, beyond a shadow of a doubt sure that everything is dead. For me, the odds seem to be about once every 3 years that this test "fails", and I'm an engineer so I don't do troubleshooting personally every day.


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PostPosted: Tue Apr 10, 2012 6:37 pm 
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As a follow up, there's a product on the market called the "CheckVolt" by Grace Engineering. It claims to meet "70E" (Z462) but that's pretty much meaningless. It is for 200-600 V equipment. It has 8 LED's on it (two redundant circuits per phase). If you see any lights at all on it, the line it is connected to is energized. This meets almost all of 70E because you can clearly see when the disconnect/breaker is open BEFORE interrupting power and verify that it is dead after. What you can't do is to test the device once power is removed. If you install a 4 pole, NO/NC push button switch in the panel wired to the "line" side of the disconnect, you can potentially use this to provide a means for testing the device before and after opening the circuit, which provides the requirements of the standard by pushing the button to test the device after power is removed.

There are other devices on the market such as some small LCD based devices that ABB makes to strap to medium voltage cables which indicate when power is removed, and many others. However as far as the Z462 standard goes they all have the inherent problem that you can't test after the circuit is powered down. There is an IEC standard for these types of fixed mount devices but so far the Z462 crew doesn't seem to have bought into that standard.


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PostPosted: Tue Apr 10, 2012 6:57 pm 

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And remember that the incident energy labelled is for some work distance. As you could measure with some "long stick", the incident energy decreases.


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PostPosted: Thu Apr 19, 2012 2:03 pm 
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Thanks for all the inputs! Really appreciate it!


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