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 Post subject: Verifing zero energy
PostPosted: Wed Apr 11, 2012 11:10 am 

Joined: Wed Apr 11, 2012 11:00 am
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Not being an electrician or skilled as a Qualified Person I need to understand how to verify zero voltage on MMCs and 480 disconnects. My dilemma involves LOTO. If a MCC or disconnect has been placed in the open position and a lock is applied, what choices are avilable to electricians or a qualified person to check for hazardous voltage?

I understand when there are draw out breakers but not where the door is closed. Thanks in advance for any assistance you may offer.


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PostPosted: Wed Apr 11, 2012 2:26 pm 

Joined: Thu Oct 27, 2011 9:34 am
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Test lights and equipment activation downstream are ways to verify the absence of voltage but from my understanding of the OSHA and NFPA 70E expectation/standard, a physical check with a voltage meter is the minimum. Obviously the meter needs to be evaluated, calibrated, tested before and after, etc. I have been on audits and conducted trainings where electricians would like to do it with a test light that lights up when voltage is near but I enforce the physical test for voltage in the panel. I am not aware of a more positive way to test for the absence of voltage.


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PostPosted: Wed Apr 11, 2012 8:00 pm 
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NFPA 70E, 110.4(A)(5): "When test instruments are used for testing the absence of voltage on conductors or circuit parts operating at 50 volts or more, the operation of the test instrument shall be verified before and after an absence of voltage test is performed."

Note also that I have found NO manufacturers that will state in writing that their non-contact voltage detectors are acceptable as devices for testing for absence of voltage below 1000 volts. Above that range, that is the tool you use (when rated for it). Below that voltage, a multimeter or an equivalent tool which accomplishes the voltage testing duty and can be tested before and after is the tool of choice. "Wiggies" are also on my ban list due to the propensity for destroying all electronic devices by means of inductive kick. In my shop, it's either a multimeter, or a multimeter except for medium or high voltage. And the multimeter must be properly rated for the transient overvoltage that can be expected (Category rating), having nothing to do with the bogus "outdoor/indoor" type ratings usually attributed to category ratings. If you do not do this and the voltage is too high or you see a transient go through the meter, it can explode and injure the electrician using it.

The reason for testing before and after is to verify operation of the meter. If there is an equivalent fail safe way to do this (I don't know of any) at the point of potential injury, then this could be an acceptable substitute for this test but you better have more than adequate documentation for what you are doing.

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Not being an electrician or skilled as a Qualified Person I need to understand how to verify zero voltage on MMCs and 480 disconnects. My dilemma involves LOTO. If a MCC or disconnect has been placed in the open position and a lock is applied, what choices are avilable to electricians or a qualified person to check for hazardous voltage?


First off, it is not ZERO voltage. It is "absence of voltage". It should be stated as absence of hazardous voltage. Generally this is attributed to meaning less than 50 volts. Especially in the case of open vacuum contactors, there is usually a little stray voltage floating around all electrical equipment and getting close to true zero voltage is only possible if you create an equipotential ground condition. This is much more critical as the system voltage goes up to the point where temporary grounds are a critical component of electrical LOTO.

There are several LOTO procedures in OSHA. Just within 1910, there is Subchapter J (familiar to most), S (electrical for utilization), R (269, electrical for distribution), and O (for production).

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I understand when there are draw out breakers but not where the door is closed. Thanks in advance for any assistance you may offer.


You must expose the wiring to test it. Simple as that. The testing process itself is done as if the equipment is energized even though it is hopefully NOT energized. You suit/glove up just as if the circuit is energized and do the test. No EEWP required because this is a task which cannot be done under safe working conditions since you can't get to a safe working condition without testing for absence of voltage. Hence one big reason for the voltage testing exception to EEWP's. With drawout breakers you are STILL required to test even though it seems like you don't have to since the line is physically disconnected. However, lots of electricians have been killed by making assumptions about how things are wired up. I've had enough "surprise" moments myself early on to be religious about test-before-touch.

The most annoying breakers are the ones with the rotary handles where you have to open the door first, and THEN attach the lock because they don't provide any means to opening or closing the door after the lock is applied. I've also banned these in new installations not only for this reason but because they bend/break with too many locks on them, and because the pin that you commonly see on some of them tends to have problems lining up with the door later on, and because the mechanism is usually not very well built. In short, get rid of these things and don't let anyone install more of them. They are nothing but trouble.

I'll give you an example of WHY you must actually test the equipment you intend to work on and not do the test somewhere else. In a mine in New Jersey I had a starter that stopped working. So I went to the disconnect and locked it out. I opened the starter up and knew that I was safe. Just as a precaution I put my meter on the starter and....voltage was present. I went back to the disconnect and opened it and found that it had actually been gutted a couple years previous, but no one had removed the labels. If I had not tested it, I would have very likely been hurt or killed. I remember this incident vividly because I actually didn't have any intention of testing it...at that moment I had second thoughts and went all the way back to my truck to get my meter to test it "just in case". It was if an angel was smiling on me that day because that little second though saved my life, and I got religion at least as far as testing for absence of voltage every time after that.

Second example: electrician goes to unwire 2 office trailers out of 3 in a mine in North Carolina. Being as all there was is a panelboard with 480 V breakers on it, he opens the two breakers, tests them at the panelboard, closes the panel door, and locked out the door. He then takes out his trusty wire cutters and begins to snip the wiring. His wire cutter welds itself to the fully live wires he was cutting into. Turns out that again, breakers were mismarked and he got "lucky" finding the mismarked breaker first.

Third example: In a foundry where we had two 2400 V to 480 V transformers in an electrical room with just the two transformers, two 2400 V disconnects, and two 480 V disconnects. Not having any 2400 V equipment, electrician went to the labelled 480 V disconnect and open this and leave the door open. Went to labelled 2400 V disconnect and open and lock this, then open the door and inspect. Then go back to the 480 V panel and check for absence of voltage. Appears dead. Then open the transformer door and begin physical inspection on transformer. Surprise! Transformer is not dead. Careful inspection reveals that both panels were mismarked and that the conduit "criss-crossed". Shortly after that, electricians got a Christmas present...2400 V testing equipment.

Fourth example: Electrician in Georgia goes to open a safety disconnect and locks it out. Electrician tests one phase but not all three. Then begins to unwire motor. Surprise! Motor is not dead. Fortunately the net effect was to destroy a screwdriver, scare the heck out of the guy, and trip the fuses. Careful inspection reveals that one of the blades in the disconnect had stuck in and thus one phase was still energized.

Fifth example: Electrician energizes main breaker on 4160 V distribution system. Electrician working on terminating some wiring on a locked out breaker fed by the main breaker gets "zapped". Turns out that especially when there is no load on the bus, vacuum breakers can easily act as voltage dividers and transfer significant voltage to otherwise "dead" wiring. Lesson here was partly use of temporary grounding but more importantly since they were changing state of the system, testing for absence of voltage should have been repeated before proceeding.

I can probably come up with a dozen of these things. It happens far too common...what you think is out there and what's really out there are two totally different things. The only defense is testing for absence of hazardous voltage.


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PostPosted: Mon Apr 16, 2012 7:04 am 

Joined: Tue May 04, 2010 6:43 am
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Location: Wyoming
"Wiggies" are also on my ban list due to the propensity for destroying all electronic devices by means of inductive kick
Are you saying that troubleshooting by using a wiggie will destroy the asscociated drive or PLC?

Thanks


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PostPosted: Mon Apr 16, 2012 11:00 am 

Joined: Mon Nov 19, 2007 5:25 am
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Location: Titusville, Fl.
Wiggies are not a form of positive means of verification for absence of voltage.


Consider referencing NFPA 70E, for the test instruments to be applied as follows:

110.4 Use of Equipment.

(A) Test Instruments and Equipment.


The above information regarding the category of the test instruments should be adequately rated per NFPA 70E as follows:

120.1 Process of Achieving an Electrically Safe Work
Condition.
(5) Use an adequately rated voltage detector to test each phase conductor or circuit part to verify they are deenergized. Test each phase conductor or circuit part both phase-to-phase and phase-to-ground. Before andafter each test, determine that the voltage detector is
operating satisfactorily.

Informational Note: See ANSI/ISA-61010-1 (82.02.01)/ UL 61010-1

[font=Times New Roman][color=#000000][font=Times-Italic][font=Times-Italic]Safety Requirements for Electrical Equipment[/font][font=Times-Italic]for Measurement, Control, and Laboratory Use – Part 1: General Requirements[/font][font=Times-Roman], for rating and design requirements[/font][/font][/color][/font]



Hope this helps...


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PostPosted: Wed Apr 18, 2012 4:27 pm 
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strings wrote:
"Wiggies" are also on my ban list due to the propensity for destroying all electronic devices by means of inductive kick
Are you saying that troubleshooting by using a wiggie will destroy the asscociated drive or PLC?

Thanks


Yes. The device is basically a magnetic coil and a slide that indicates roughly the voltage. When you disconnect it, the coil discharges back into the system with a massive inductive kick that easily destroys triacs and similar devices. They cannot be used with semiconductor circuits of any kind because of the transient they cause. They may not destroy it today or tomorrow but you will have massively lower reliability. All manufacturers of PLC equipment have specifically posted notices warning not to use these things for years.

Furthermore, Wiggies have had a notice posted about them with respect to "Category Rating" for quite a while. Wiggies are subject to exploding from transients or if accidentally applied to too high of a voltage.


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PostPosted: Thu Apr 19, 2012 12:56 pm 
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A few years ago I saw a wiggy blow out it's guts when testing a 480V fuse. Wiggies are coiled wire around an armature. When the voltage is removed the coil's magnetic field collapses inducing a large voltage spike. Ignition coils on cars work the same way to fire spark plugs.


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PostPosted: Tue Jun 12, 2012 12:10 pm 

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I want to initiate a discussion on the acceptable work practices using, or more importantly not using non contact voltage detectors. My general perspective is that the industry has started to rely on a less than adequate device for the safety of our people. Irrespective of person’s interpretations of codes, standards, or regulations, what is the right thing to do?
With the detailed digging into the methods of how these non contact devices work, then following this up with all of the stated, implied, or other usage restrictions by the vendors, it amazes me that our people in the work force are relying on these devices for their life.
I have recently authored a global directive to the company that I work for that restricts the usage of non contact voltage detectors and mandates contact type devices be used as the final step in verification of deenergized condition.
I sure that one would argue that a qualified competent person would understand the limitations of the devices and that the individual would know how to properly use them and I would respond that you’re kidding yourself. There’s not one person that I know that doesn’t have some amount of complacency, in that if you rely on a device time and time again that when that instance arises that the usage of the device falls into the grey area of the devices capabilities, do we rely on it? Unfortunately the answer is yes, and then that the next near miss, LTA, or even fatality.
To list some shortfalls with the devices: doesn’t work on shielded cable, doesn’t work on DC, doesn’t work on 3 conductor cable, doesn’t work on low current applications, not calibrated device, doesn’t detect voltages <90 VAC, wont detect stored energy, wont detect for cable in conduit, less reliable with thick insulation, erroneous signals in heavy electrical noise environment, won’t work if user is insulated from ground. If you’re a vendor don’t respond, or do so stating you’re a vendor.


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PostPosted: Wed Jun 13, 2012 3:58 am 
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Although I may agree with all the reasons stated to ban the device and I've done so myself, there are strong reasons why noncontact voltage sensors are necessary.

If you are working at or below 1 kV, you'll get no argument from me.

If you are working above 1 kV however, the only "contact" meter is a phasing meter. These are not all that accurate and reliable either and the manuals for these things will give you second thoughts about them. The standard tool in the utility industry for "test before touch" is a noncontact voltage meter for applications above 1 kV. There is even an IEC standard for this. Granted EVERY claim you made about why to avoid them still exists even at elevated voltages. On shielded cable, they have a device called a capacitive tap built into the connectors that reliably allows voltage readings and without it, you can't get a reading. However since the current is too low for standard noncontact meters, a special meter is needed.

This is assuming AC. For DC above 1 kV, there is no corresponding IEC standard and you are on your own. I''ve found one particular phasing meter meant for checking HV capacitors for charge that seems to be good enough for use up to 69 kV (but only reads up to 50 kV) on the market, but that's it. Since I have an electrostatic precipitator theoretically capable of far beyond this voltage, it would be nice if there was something else out there.


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PostPosted: Wed Jun 13, 2012 5:02 am 

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Hubble makes a calibrated device for applications below 69 kV. Also on the capacitive tap, that's one of the items that brought this issue up. I haven't recieved full detail on the issue, hoever we had instance that this did not detect voltage on a hot system, not sure if the term was faulty of if the grounding method of the shield/system played into it. Granted we don't normally work with voltages at the utility levels, we do encounter voltages below 30kV (generator output and below).

For precipitators, since the energy level is low, I have always used HV test probes, I wont say their exactly rated for that but that the only type I know to use.


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PostPosted: Wed Jun 13, 2012 7:58 am 
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[font=Tahoma]I agree with your concern about the limitations of noncontact testers; however, I believe they are a useful device and wouldn’t ban their use, even for low voltage.[/font]

Banning noncontact testers and requiring only the use of digital mulitmeters does NOT make voltage testing idiot-proof. Qualified workers must still be trained to follow safe work practices such as lockout, live-dead-live testing, reading their test equipment’s user manual, understanding it’s limitations, voltage and CAT ratings; then they must evaluate the equipment they going to test and determine its voltage, evaluate it for any stored energy or possibility of induced voltages, determine the shock hazard, arc flash hazard and don the appropriate PPE.

Inside the plant (480V and below), I use a noncontact tester as a quick troubleshooting tool, but always test with a digital multimeter when establishing an electrically safe work condition. Wiggies on the other hand, shouldn’t be used anymore due to safety issues and potential damage to equipment; we have also banned any other meters that don’t have a CAT rating. Outside the plant we encounter higher voltages (i.e. padmounted capacitor bank - 13.2kV) and use only a noncontact tester to verify the absence of voltage.

There is an interesting article on Fluke’s website by Jim White from Shermco Industries, Inc. on testing for the absence of voltage; it covers proximity testers, electrical testers and digital mulitmeters.

[url='http://support.fluke.com/find-sales/Download/Asset/3392477_6003_ENG_B_W.PDF']http://support.fluke.com/find-sales/Download/Asset/3392477_6003_ENG_B_W.PDF[/url]



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PostPosted: Wed Jun 13, 2012 9:14 am 

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Your point is on target, however I want to point out a key difference to the posting I made. The word "BAN" was not used. The words used are "[font=Calibri]restricts the usage of non contact voltage detectors and mandates contact type devices be used as the final step in verification of deenergized condition"[/font]

[font=Calibri]Absolutly agree that this step, performed with any test device needs to be performed by a qualified person. Excellent reference as well.[/font]


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PostPosted: Tue Jul 03, 2012 10:51 am 
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Tired wrote:
Not being an electrician or skilled as a Qualified Person I need to understand how to verify zero voltage on MMCs and 480 disconnects.


Why? If you need to verify voltage, get someone qualified to do so or get qualified.


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