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 Post subject: Creating electrically safe work conditions with permanently mounted voltage detection
PostPosted: Wed Aug 31, 2011 12:48 pm 
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This white paper (draft) covers the core LOTO issues in using permanently mounted electrical safety devices. Since many of you are using such devices, I would like to have your comments on this white paper.

Since the procedures contained in NFPA 70E 120.1(1)-(6) /CSA Z465-08 4.2.1 were written around around portable voltage detectors, I would also like to get your comments on ways (if any) these procedures could better accommodate permanent voltage detection devices.

You can get this paper at:http://www.graceport.com/pesd.cfm

thanks phil


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PostPosted: Thu Sep 01, 2011 3:32 pm 
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SOSDD?

http://www.arcflashforum.com/showthread.php?t=1730


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PostPosted: Fri Sep 02, 2011 5:30 am 
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This appears to be a different device than was the subject of the previous thread. That device was an indicator only. The Thru-Door voltage detector might satisfy NFPA 70E LOTO procedures. See http://graceport.com/assets/files/Data%20Sheets/Thru-Panel_Voltage_Detection_Fits_NFPA_70E.pdf. The question is, do you trust the capacitive voltage detection to be reliably there whenever the voltage is present on the bus? I think it would be acceptable if you tested the voltage before de-energizing and it showed voltage present.


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PostPosted: Fri Sep 02, 2011 9:15 am 
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"120.1(5)... Before and after each test, determine the voltage detector is operating satisfactorily."

Also known as "test the tester, test the circuit, test the tester." The second test ensures the tester did not fail following the first test.

With any permanently mounted device, the only way to perform the second test would be to re-energize the circuit; but that would then require us to start over at number 1.

Phil is asking us to wave the second test because it was written around portable devices and is not a "core" part of 120.1.

Fig 1 states the capacitance to the NCVD is fixed. The rest of the circuit involving a human in the ground path is not fixed, and will vary with how the device is held and how the person operating it is standing.


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PostPosted: Fri Sep 02, 2011 9:26 am 
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You could say that the voltage detector is the portable instrument that you touch to the capacitive device. You can test on an energized panel that also has the thru-panel capacitive device.

Wouldn't this be the same as testing a 15 kV loadbreak elbow at the capacitive test point. On deadfront MV equipment, there is no other practical way to test if the equipment is energized.


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PostPosted: Fri Sep 02, 2011 9:28 am 
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Interesting article and concept.

First problem I see is the person testing for voltage is relying on a cheap $12 NCVT that may or may not work. I've seen several NCVT's on the market that aren't cat III or UL approved and made in China. I'm not sure I would be willing to put my life on the line based on China's quality control standards.

Second, NCVT's in my experience have a hard time isolating a non energized conductor in panels where other energized conductor are present, especially 480 volts. Seems the test ports are pretty close together so you are relying on the senstivity of the NCVT to pick out a non energized leg. Although I guess the point is testing if it's de-energized. What if the tester is not functioning and tells you all phased are dead?

Third, what's stopping someone from sticking a screwdriver in the test slot and breaking off the insulating material? Or breaking off the tip of the NCVT? Granted this might not happen but I've seem some pretty strange suff that makes good fodder for the Darwin awards. :eek:

I guess my biggest concern is relying on a bargin basement NCVT. Our policy is non contact voltage testers are not allowed to be used for anything that requires hand - conductor contact, or used as a LOTO test device.


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PostPosted: Fri Sep 02, 2011 12:40 pm 
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I don't believe a human is used in the test circuit when measuring voltage on an elbow. Controlled capacitance to the test point with another meter lead directly to ground.

Vincent had the final word when this was discussed before: http://www.arcflashforum.com/showthread.php?t=505


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PostPosted: Sat Sep 03, 2011 5:50 am 
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stevenal wrote:
"The rest of the circuit involving a human in the ground path is not fixed, and will vary with how the device is held and how the person operating it is standing.


What if they are in an insulated lift? What if they are wearing EH rated boots?


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PostPosted: Mon Sep 05, 2011 9:22 pm 
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geh7752 wrote:
Third, what's stopping someone from sticking a screwdriver in the test slot and breaking off the insulating material? Or breaking off the tip of the NCVT? Granted this might not happen but I've seem some pretty strange suff that makes good fodder for the Darwin awards. :eek:


What is to stop someone after verifying an isolated state, from sticking a screwdriver on the line side of the breaker? Throwing a glass of water in the cubicle? Putting sheet metal screws through the insulation on 15 kv cables (I know where this happened during constrcution)..99.94% of us would NEVER dream of it.. But that is why they have Darwin awards.. "Only the strong and smart will survive..."

The way one client uses the Grace lights in their facilities is by educating and labelling what a normal operating one should look like and what an isolated one looks like. IF an operator goes to isolate a piece of equipment and the lights a) don't look as they are supposed to, or b) don't go out when they open the switch they are trained to call a qualified electrician to repair and isolate the equipment.

I have found one instance where the light would not show an isolated piece of equipment with the brekaer open. It was on an older VFD and it was reading the discharging DC bus on the drive. After verifying with a meter, we applied all the locks needed and but in a work order to remove the light as it was not right for the application..


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PostPosted: Tue Sep 06, 2011 7:25 am 

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glen1971 wrote:
The way one client uses the Grace lights in their facilities is by educating and labelling what a normal operating one should look like and what an isolated one looks like.


Great Point! Isn't the "education" concept similar to educating people to understand ground fault indicating lights? Is the light burned out or do we have a ground fault?


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PostPosted: Thu Sep 15, 2011 9:22 am 
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Zog wrote:
What if they are in an insulated lift? What if they are wearing EH rated boots?


Even more variables in the capacitive test circuit. Added dielectric thickness alters the capacitance to ground.

My point was not that putting the human in the capacitive test circuit was dangerous in itself, it is that expecting consistent results with so many variables may lead to a dangerous action.

The following is a statement from the manual from the Fluke Voltalert tester. The fourth bullet point backs up my concern:

When using the Tester, if tip does not glow, voltage could still be
present. The Tester indicates active voltage in the presence of
electrostatic fields of sufficient strength generated from the source
(MAINS) voltage. If the field strength is low, the Tester may not provide
indication of live voltages. Lack of an indication occurs if the Tester is
unable to sense the presence of voltage which may be influenced by
several factors including, but not limited to:
●● Shielded wire/cables
●● Thickness and type of insulation
●● Distance from the voltage source
●● Fully-isolated users that prevent an effective ground
●● Receptacles in recessed sockets/ differences in socket design
●● Condition of the Tester and Batteries


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PostPosted: Wed Nov 16, 2011 8:19 pm 
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A little late but I considered one alternative on the Grace devices.

Connect up a switch to the thing so that you can switch between taps on the line and load side of the disconnect, also with an "off" position. Not exactly clean but it allows one to test both "hot" and "off" settings both before and after the disconnect is opened.

Similar situation recently came up. It's the DC voltage side of an electrostatic precipitator. The whole ESP is basically a capacitor hooked to a large transformer with a HV rectifier running at around 60 kV max. That is OUTSIDE the range of even class 4 gloves so gloves won't work. Hot sticks are sort of OK but have been unable to locate a suitable HV meter.

So the idea here is to use the internal voltage divider and analog meter that is already installed on the unit. An external low voltage (9 V battery) source is used as the "test voltage" to validate that the meter is working.

In both instances obviously you want to test the circuit both energized and de-energized since there's always a small chance that the test circuit wiring and/or switch is defective.

I've looked at the codes 6 ways from Sunday about this and I can't see any valid reason to invalidate this idea.

As to testing above 1 kV AC, both online and capacitance type testers are considered acceptable (of course with the various cases) under IEC standards. There really isn't a U.S. equivalent that I know of. Below 1 kV, there are no standards for capacitance type testers and since they are not necessary, I see no reason to use one. Many of them have something right in the instructions that says specifically that they are not to be used for safety purposes and that warning is good enough for me. As a troubleshooting device ONLY, I'd consider them OK. But as a safety device (along with Wiggies), not such a good idea. Plus Wiggies destroy semiconductors with their inductive kick.


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PostPosted: Wed May 23, 2012 12:37 pm 
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phil2331 wrote:
This white paper (draft) covers the core LOTO issues in using permanently mounted electrical safety devices. Since many of you are using such devices, I would like to have your comments on this white paper.

Since the procedures contained in NFPA 70E 120.1(1)-(6) /CSA Z465-08 4.2.1 were written around around portable voltage detectors, I would also like to get your comments on ways (if any) these procedures could better accommodate permanent voltage detection devices.

You can get this paper at:http://www.graceport.com/pesd.cfm

thanks phil

The article was interesting. I am going to send it to my manager, who is also a licensed electrician. It may be something we are interested in. So that I understand, it recommends installed this device, and then also using a hand held device to verify it. Would you need to install the device on everyone of your panels?

_________________
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PostPosted: Fri May 25, 2012 12:51 pm 

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We do not allow NCVDs for safety testing as a policy. Where dangerous AFIE (> 40 cal) is available, is there a device for closed door absence of voltage testing on 480 VAC equipment? If I fuse the test port wiring at 20 A then it could permit a safe, convenient procedure such as the following:
  • View the LED indicator to verify it indicates voltage is present
  • Use a sufficiently rated meter to verify voltage is present at the test port (wearing gloves and Level 0 PPE)
  • Isolate the power feed
  • View the LED indicator to verify it indicates voltage is no longer present
  • Use the meter to verify voltage is no longer present at the test port (same PPE)
  • Test the meter on a different, energized source to verify it still works (PPE depending on alternate source)
  • Proceed to open covers and repeat the absence of voltage test inside the cabinet (same PPE)
Any thoughts on the availability of such a test port or on this procedure? I've thought about using an EU-style 3P/ 4W receptacle as a test port since that would be highly unlikely anyone would try to plug in a device here in the US.


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PostPosted: Fri May 25, 2012 1:18 pm 
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garyc wrote:
....Use a sufficiently rated meter to verify voltage is present at the test port (wearing gloves and Level 0 PPE)

How can you assure that there is no arc hazard at the test port?


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PostPosted: Fri May 25, 2012 3:38 pm 
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garyc wrote:
Any thoughts on the availability of such a test port or on this procedure? I've thought about using an EU-style 3P/ 4W receptacle as a test port since that would be highly unlikely anyone would try to plug in a device here in the US.


You said fused. Bad idea. How do you know if the fuse hasn't tripped or voltage is actually absent? What about using a PT (transformer) instead to lower the voltage to a safe level and mounting banana plugs in the front to take a measurement? It is common practice in utilities to use PT's to verify the absence of voltage since it is effectively impossible to measure some voltages directly.

Grace Engineering also sells "test ports" that make it possible to use a noncontact voltage tester to test for absence of voltage which does as you describe, except that these very same devices are clearly labeled and not accepted anywhere in any Code as a valid device to test for the absence of voltage because they will produce both false positives and false negatives.

Grace is not the first shameless company to claim their equipment is "70E compliant" either, whatever that means. Melcor has been recently doing some similar shameless advertising with their dead front receptacles.


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PostPosted: Sat May 26, 2012 11:43 am 

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Thank you for your thoughts. Of course the hazard exists and the equipment must be treated as energized until isolated/ locked-tagged, and verified. The purpose of these devices is to reduce risks, and since there is no acceptable PPE for > 40 cal I have a predicament for my 480 VAC service entrance equipment.

jghrist: Fuses supplying the test port would interrupt the fault quickly and thus reduce the hazard.

PaulEngr: The procedure requires testing the ports to detect voltage before and after isolation, just as the LEDs must be viewed before and after isolation to be of any use. If a fuse has tripped then it should be detected at this time. Contact testing after covers are removed is still required to establish an electrically safe work condition, but at a significantly lower risk since isolation has already been indicated by both the LEDs and the test port.


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PostPosted: Sat May 26, 2012 2:48 pm 
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garyc wrote:
Thank you for your thoughts. Of course the hazard exists and the equipment must be treated as energized until isolated/ locked-tagged, and verified. The purpose of these devices is to reduce risks, and since there is no acceptable PPE for > 40 cal I have a predicament for my 480 VAC service entrance equipment.


I disagree that you can't do anything at all. If an arcing fault does not or cannot occur, then no hazard exists. IEEE 1584 and other methods give us a way to calculate the magnitude of the hazard. They do not provide insight into whether or not the hazard actually exists.

From 70E under definition of arc flash hazard, Informational Note No. 1, "An arc flash hazard may exist...provided a person is interacting with the equipment in such a manner that could cause an electric arc."

From section 130.7, Informational Note No. 2: "It is the collective experience of the Technical Committee on Electrical Safety in the Workplace that normal operation of enclosed electrical equipment, operating at 600 volts or less, that has been properly installed and maintained by qualified persons is not likely to expose the employee to an electrical hazard."

Clearly although the best that 70E gives you is an extremely incomplete hazard analysis procedure in Annex F, the intent is to perform a risk assessment. In some cases although as you said, a hazard does exist, the likelihood that it occurs may be so remote that the risk is acceptable even with a very high severity (>40 cal/cm^2).


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PostPosted: Sun May 27, 2012 11:59 am 
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garyc wrote:
Thank you for your thoughts. Of course the hazard exists and the equipment must be treated as energized until isolated/ locked-tagged, and verified. The purpose of these devices is to reduce risks, and since there is no acceptable PPE for > 40 cal I have a predicament for my 480 VAC service entrance equipment.


If you are trying to isolate the service entrance for your switchgear, wouldn't an electrician be there to verify the isolation? If the service entrance is in a piece of switchgear, and without knowing the intimacies of how your system is set up, why not check for voltages downstream of the main disconnect? If you are in an MCC, and assuming that your AF rating is lower after the switchgear's Main Breaker, why not put on the appropriate PPE and check for voltage in a starter/breaker cubicle in the line up? Then isolate and check for the presence of voltage at the same place, while still in the PPE for that cubicle.

Just a thought.. I know I have had to measure voltages once the utility has completed work, or if a generator is online, and went downstream of the main breaker in a cubicle and checked the voltages there.. Keeping in mind that the AF rating in a cubicle would be the same as the LOAD side of the Main Breaker....


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PostPosted: Wed May 30, 2012 8:27 am 

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Most of the service entrance switches/ circuit breakers are in a single outdoor switchboard with busduct into the building to feed another switchboard. We don't test downstream because often the incident energy is still > 40 cal at that point, and there is a risk that personnel could test at the wrong place.

Our policy is not to remove covers until the utility has deenergized. We have either LED flasher devices or power meters at these locations, which help us confirm the utility has switched the correct service. I'm just considering whether to add a physical contact test point for further risk reduction prior to cover removal. It doesn't sound like anyone is doing that today.


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