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 Post subject: How to confirm equipment de-energized for hazard category >4?
PostPosted: Tue Oct 29, 2013 12:48 pm 
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We are supposed to treat all equipment energized until proved otherwise by testing for absence of voltage. This means that even though we have secured any source of energy feeding a given enclosure, in order to perform the verification test we want to don the proper PPE before opening the enclosure and only after confirming absence of energy we can remove our PPE.

This is my dilemma: "how do you perform verification of absence of energy for a piece of equipment that falls under the hazard category of DANGER (i.e. greater than category 4)?" Since there is no adequate PPE for accessing this cabinet, how am I supposed to test for absence of energy?


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PostPosted: Tue Oct 29, 2013 7:02 pm 
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The "40 cal" cutoff turns out to have no scientific merit. It is removed in the 2015 draft. Second pay attention to the definition of an arc flash. You must interact in such a way as to cause it. Third, why not go to upstream or downstream locations where adequate ppe is available and do a screening test there first, thus lowering the risk substantially? Finally, not doing maintenance due to fear of a hazard is a sure fire way to guarantee it. The failure rate on breakers in particular over time is downright scary. It is mostly due to basics of lubrication.


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PostPosted: Wed Oct 30, 2013 4:51 am 
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Thank you Paul. After reading a bunch of other similar threads I've started to come to the same conclusion - no work above 40 cal is somewhat of an arbitrary limitation with no specific directive in the regs. However, in regards to one of your suggestions I'm still on the fence...don't you think that testing with a contact voltmeter qualifies as "interacting in such a way that has the potential of causing an arc flash"?
I like the suggestion of testing upstream/downstream where adequate PPE is available and, although technically is not the same as testing right inside the enclosure of interest, I think that in most instances you can make a reasonable case that you've verified absence of energy at your location.
I completely agree with you that while we need to be aware and respect the arc flash hazard, its existence should not become a reason for not conducting maintenance!!!


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PostPosted: Wed Oct 30, 2013 6:59 am 
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Let's consider the potential causes of voltage and arc flash for that matter and move on from there.

Take for example a common situation that arises that I have to deal with. You have a 480 V distribution panelboard that is connected directly to the transformer secondary. In days gone by, this was a pretty common setup. Since the main breaker is on the transformer secondary, the biggest cause for concern is if an arc flash initiates at the incoming lugs, or even if the energy is high enough that it starts somewhere else inside the same panel and then jumps across the main breaker to the line side. Generally these tend to have very high incident energy levels, frequently over 40 cal/cm^2. Let's just for the sake of argument assume that it is 150 cal/cm^2, a point where there truly is no available PPE, and even an arc flash blanket probably won't do any good.

Now before you open the panel, consider what would or could happen while opening the panel itself. Is there a chance that conductive dust could fall into the panel? Is there already signs of corrosion external to the panel? What indication do you have that a failure could occur just while opening the panel? For that matter, is the panel screwed on (which most of them are), and could it fall into the panel and short something out while attempting to remove the panel? If your answer is yes to any of these questions, then there is a risk of an arc flash while simply removing the cover. Finally consider work position and ergonomics and whether or not it is possible to stumble or simply be startled by a loud noise somewhere else and accidentally fall into the enclosure. None of these are insurmountable issues though and it is certainly possible to remove the cover without causing an arc flash.

Next we move onto your original question...that of using a voltmeter. First question...do you have EXPOSED connections? By this I mean are there any places in the panel where the wire was not stripped to the correct length specified by the manufacturer, where there are exposed bus bars, etc., where there is a potential for inadvertent contact? If so, can you insulate either the equipment or yourself, or use insulated tools (hint...meter probes are insulated) to protect against inadvertent contact? Is it possible for your meter probes to short phase-to-ground or phase-to-phase if someone slips while checking for voltage? Note that most meters these days come with probe caps that limit the exposed surface to a bare minimum for this reason so that shorts with the probes are impossible. If you can basically do all the things necessary to prevent both a shock hazard and accidentally bridging a phase while testing for absence of voltage...again, unlikely to cause an arc flash. But there are some obvious precautions, too. For instance don't disturb the wiring and go rooting around in a box. If you have to move wires around to do some testing, then don't do it with the power on.

These are all considerations that one would do by performing a risk assessment (job hazard analysis in this case) for a specific task, that of testing for absence of voltage. Now getting back to the other question...we need to be smart about the possible sources of electrical energy and to isolate and test them. If I have say a portable power tool, when I pull the plug, I've physically isolated the equipment. Especially in these days of increasingly more sophisticated controls in almost everything, I need to test for possible sources of internal stored energy (batteries, capacitors, static charges). Once I'm satisfied that these do not exist, I can proceed with the work. Now this basic concept applies whether the equipment is a drill or something much larger. For instance in the case above of a 480 V panelboard fed by a single transformer, the disconnect on the primary side normally isolates all power and testing there for absence of voltage would be just as effective as downstream, except for detecting other sources (capacitors, static charges) when you can visually verify everything. Frequently in an industrial site no matter what the print shows, you can't trust the equipment to follow the prints.

Once I've isolated the sources of energy and tested to verify that there is no energy present I can proceed with the work. In some cases though this becomes a much more difficult proposition. These are:
1. If you can't actually de-energize everything within an enclosure or you can't be 100% sure of this. A common example is with MCC's where the incoming stabs may not be de-energized, and where quite frequently you have common control power so that you can't isolate control voltage. In these cases the definition of the "work area" may be only a small area within the equipment and testing may need to be more thorough.
2. Consider other sources that you may not readily think of. For instance when dealing with overhead power lines, three potential sources of energy include wind (induced), induction from other parallel nearby power lines, other personnel unknowingly coupling a generator to a de-energized line, and lightning. Another common industrial problem is capacitors that can store significant DC energy. In these cases your only defense is equipotential ("work site") grounding to ensure that a de-energized line stays de-energized.
3. There are other energized lines that run through the same enclosure/raceway that are not electrically part of the circuit but may be a hazard either just because they are physically present but were not previously known, or that can create induced voltages/currents in equipment to be worked on.

Notice however that despite a significant potential shock hazard, the arc flash hazard in almost all of these special cases is either nonexistant for voltage testing purposes (an insulated wire that runs through the work area would not be considered an arc flash hazard while testing for absence of voltage), or the potential incident energy is typically (but not always) quite limited such as the amount of stored energy in a capacitor or battery. The number of cases where this would be in question is usually a small number that can be addressed as exceptions to be aware of and would be found while doing the arc flash hazard analysis in the first place.

Notice also that you can't just have a single rule to cover all situations and all tasks. Doing a risk assessment (JHA, JSA, PTP, etc.) needs to be equipment and task specific especially for tasks where there is a significant risk associated with it. Even in the current (2012 edition) 70E, the so-called "40 cal rule" (which is only an informational note, not part of the standard) states, "When the incident energy exceeds 40 cal/cm^2 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 wires". The key is greater emphasis, not outright banning work in this case. So regardless of whether you want to go by the strict wording used in 70E-2012 or not, even the informational note clearly does not ban all energized activities but sets a limit on when someone should spend more care in planning the task.

Notice also that testing for absence of voltage arises in Article 120 dealing with de-energizing equipment. It is definitely outside the scope of 130.2 since otherwise you'd have a catch-22 condition (can't de-energize to do work because it is energized work but can't work energized...). This places testing for absence of voltage as part of de-energizing outside the scope of 130.2(B) (requiring an EEWP), even though 130.2(B)(3) has an exception for diagnostic work such as voltage testing.


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PostPosted: Wed Oct 30, 2013 7:17 am 
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Thanks again Paul. I'm sold on all of the scenarios and associated assessments you present. I also agree with your views on the "catch-22" condition...this is how I had been looking at it but it is reassuring that I'm not taking unjustified liberties and other professionals regard it the same way.


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PostPosted: Mon Nov 04, 2013 6:32 pm 
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Paul, what are your thoughts on verification of the absence of voltage on a 3 phase system where one tests each phase to ground for the absence of voltage in oppose to phase to phase- L1- L2, L2- L3 and L1-L3. Knowing that an arc could be initiated - pending on the test probes with testing phase to phase method. With testing for the absence of voltage each phase to ground would alleviate this.

Thank you


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PostPosted: Mon Nov 04, 2013 7:45 pm 
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The only two ways that I have read or seen an arc initiated from voltage testing is first with "wiggies" that were pretty well known for exploding, and one case about 15 years ago before category ratings on meters where the transformer was wired backwards. At this point with a properly rated meter and given that the internal resistance is typically in the megaohm range, it eliminates at least the risks that I am aware of. Measuring phase to ground on a 3 phase system gives you a voltage that is 1.732 times less than line to line but this is not significant from a safety point of view, and if it is ungrounded or impedance grounded, even due to a failure, you will see full line voltage from phase to ground anyway. If the meter is properly rated and properly used, and the probes are rated for the voltage (watch out for this on some of the alligator clip and banana jack looking ones), and insulated to prevent an arcing fault if the probes slip from too much coffee jitters. This is the case REGARDLESS of whether you measure LL or LG.

Proper procedure especially when doing maintenance work is to measure both between all phases AND phase to ground on all phases. Otherwise you can have a potential present and not even know it. I know that the number of cases where this happens are realy rare, but they do happen such as if 3 phases are shorted together and also contacting ground and on a large motor lead where the breaker did not trip due to a high resistance cable fault and short circuit settings were not low enough to trip. At a minimum I have read guidance saying that this is 6 checks but realistically I would not recommend any less than 4. It does not matter whether you do 3 to ground and 1 phase to phase or 3 phase to phase and 1 to ground.


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PostPosted: Tue Nov 05, 2013 5:39 am 
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You could also install low fault level test points. These are typically voltage rated banana style sockets which can be purchased colour coded which are protected by either fuses or circuit breakers (sometimes 2 different sizes in series to allow for high fault breaking capacity). You test these before and after switching for verification. They can also then be used for other testing such as phase rotation. A full isolation would be required for installation and commissioning.


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PostPosted: Tue Nov 05, 2013 12:48 pm 
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Giovanni Paradiso wrote:
We are supposed to treat all equipment energized until proved otherwise by testing for absence of voltage. This means that even though we have secured any source of energy feeding a given enclosure, in order to perform the verification test we want to don the proper PPE before opening the enclosure and only after confirming absence of energy we can remove our PPE.

This is my dilemma: "how do you perform verification of absence of energy for a piece of equipment that falls under the hazard category of DANGER (i.e. greater than category 4)?" Since there is no adequate PPE for accessing this cabinet, how am I supposed to test for absence of energy?


At a bare minimum, I would install permanent electrical safety devices (PESDs) into the electrical cabinet. These devices wrapped into your procedures, would pre-verify the absence of electrical energy to reduce the risk that voltage exists when you check it with a meter. They are cheap and easy to install--30mm holes.


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PostPosted: Tue Nov 05, 2013 6:22 pm 
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pesd's are only recognized by an iec standard at medium voltage. That leaves us with yet another piece of hardware to fail or cause failures if it is only supplemental.


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PostPosted: Wed Nov 06, 2013 6:23 pm 
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Hi All

Thanks allot for the replies. Very helpful

All the best


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PostPosted: Fri Nov 08, 2013 6:40 pm 
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I would not trust installed volt detectors.. the only way to be sure is to test the test instrument against a known source, test the specimen and then test the test instrument.

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PostPosted: Tue Nov 12, 2013 10:01 am 
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Remember that medium to heavy grounding systems are available with eyescrew attachments for use with fiberglass hotsticks. Both contact-rated and non-contact rated voltage detectors are also available with hotstick attachments. It is very common to apply personal protective grounds from the outer edge of the prohibited approach boundary and thereby reduce the arc-flash hazard at the worker to a much lower level.


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PostPosted: Tue Nov 12, 2013 7:02 pm 
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In addition to the valid comments already made, I suggest that another angle on the problem is this. Look at the Informational Note 1 on Page 31. "...where the risk is considered low... the hazard/risk category number has been reduced by 1, 2, or 3 numbers respectively."

Just because the isolated conductors must be treated as live doesn't necessarily mean that exactly the same control measures must be applied as if they were actually live. They are a bit like Schrodinger's cat -- neither actually live nor actually dead and the truth cannot be known without opening the box and doing the test. Just because a task is prohibited when actually live doesn't mean that it should be prohibited when isolated but not yet proven de-energised.

How often is a circuit isolated and then when tested for dead found to still be live? Perhaps one in a thousand or so cases? Whatever the figure, it is an indication of the reduction in likelihood and hence reduction in risk of an accident compared to doing the same task when actually live. If the likelihood has been reduced by several orders of magnitude then it is valid to reduce the hazard category accordingly. I suggest that in this case testing for dead using Cat 4 control measures would be quite satisfactory. The control measures are a function of risk, which includes likelihood. Ignoring the likeliood element of risk results in all sorts of unhelpful distortions.


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PostPosted: Tue Nov 12, 2013 7:45 pm 
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Nice try with looking at risk but the 70E Technical Committee gog it wrong. Reducing PPE implies reduced incident energy. If the likelihood is reduced sufficiently then it implies no PPE required. Your example of 0.001 likelihood of finding equipment still energized is probably optimistic from experience. For such a task depending on what human performance methodology you use, the lowest likelihood is perhaps 1%. As a general rule LOPA method published by CCPS uses 10%. However when you begin to include other task-based considerations it is indeed true that you can get to the point where arc flash PPE would not be required, and this is the case that I was making. If the likelihood is acceotably low then have at it. Otherwise the risk is too great since the estimated incident energy exceeds the PPE worn. This point could happen at any incident energy level, not just 40 cal/cm^2. Its just that the current edition of 70E calls it out. Also note that in the 2015 draft, the 40 cal "limit" is removed, there is a table of tasks where no PPE is required, and the reductionof H/RC levels is gone.


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