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 Post subject: Shock protection, 120v, gloves & inadvertent movement
PostPosted: Mon Apr 09, 2012 2:05 pm 

Joined: Mon Mar 19, 2012 1:21 pm
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Table 130.4(c)(a) lists the restricted approach boundary for 120 volts as "avoid contact". The column heading says "includes inadvertent movement adder". What does this mean?

If a qualified person needs to do voltage testing on a 120v circuit do they need to wear appropriately rated rubber gloves?


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PostPosted: Mon Apr 09, 2012 4:35 pm 
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Location: México, D.F.
Use Rubber Gloves Class 00 (500V). Look for Salisbury, Magid Glove, Electrosoft, Novax, etc.


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PostPosted: Mon Apr 09, 2012 4:36 pm 
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Use Rubber Gloves Class 00 (500V). Look for Salisbury, Magid Glove, Electrosoft, Novax, etc.


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PostPosted: Mon Apr 09, 2012 6:04 pm 
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Inadvertent movement adder comes from the original source (IEEE 516). At 120 VAC they aren't including one. At higher voltages, you have to consider the possibility that someone moves accidentally in such a way that they could receive a shock. Hence the reason for using insulated tools and/or gloves when you are going to cross the restricted approach boundary.

Although you see more discussion about this in the utility business, there are 4 METHODS for avoiding shock:
1. Safe working condition. Basically, eliminate the risk. However you have to use one of the other 3 methods to get there.
2. Rubber glove method. Insulate yourself and make direct contact. Also you have to insulate the nearby lines with cover up materials (blankets and line hose), essentially out to the restricted approach boundary with 100% coverage on different phases and covering the phase to be worked on within the restricted approach boundary.
3. Insulated tool method. Use insulated tools which are insulated both to prevent a phase-to-phase failure AND to protect the worker from contact. Tool must be long enough to extend outside the prohibited approach boundary. Note that mixing 2 and 3 doesn't work...effectively #3 disappears and you are just using rubber glove method when you do this. Hot sticks actually conduct a minute amount of charge on them when they are working correctly.
4. Live line, bare hands method. This involves wearing a set of conductive coveralls, gloves, and even socks. The worker uses either a boom truck or insulated ladders or helicopters to move into position and then "ground" themselves to the live line so that they are the same voltage as the energized line.

I'm not entirely sure why method #3 gets almost entirely ignored by non-utility folks even though 70E clearly has procedures for using insulated tools, and the tables refer to rubber gloves OR insulated tools.


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PostPosted: Thu Apr 12, 2012 2:28 pm 

Joined: Mon Mar 19, 2012 1:21 pm
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So just to be clear...

Upstream panel = category 0

Testing for voltage on a 120volt circuit requires 00 rubber gloves and leather work gloves (along with rest of category 0 PPE).

The fact the NFPA70E table 130.4(c)(a) says "avoid contact" for the restricted approach boundary for 120 volts does not infer that the employee does not need rubber insulating gloves, correct?


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PostPosted: Thu Apr 12, 2012 6:48 pm 
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racineboxer wrote:
So just to be clear...

Upstream panel = category 0

Testing for voltage on a 120volt circuit requires 00 rubber gloves and leather work gloves (along with rest of category 0 PPE).


No, leather protectors are required over rubber gloves. It's not the same thing. AND, you don't have to wear leathers over class 00 gloves in some special cases that I never remember (because we ignored the exception everywhere I've worked).

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The fact the NFPA70E table 130.4(c)(a) says "avoid contact" for the restricted approach boundary for 120 volts does not infer that the employee does not need rubber insulating gloves, correct?


No, it says avoid contact. There are two work methods for doing this. You can either use insulated tools or you can use rubber gloves. Your choice. This is no different than working on an overhead line except that the tool lengths are a lot smaller. That's the purpose of those expensive "1000 V insulated tool" sets with the orange handles and the insulated meter probes.


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PostPosted: Fri Apr 13, 2012 6:10 am 

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Thanks for the help Paul. You're helping me out even if it seems I'm asking the same questions over and over. :) The verbage and tables and footnotes within the tables can be a bit confusing.

So I went back and re-read the section on hand protection and see the difference between "heavy duty leather gloves" and "leather protectors". Sorry for the screw up in verbage.

The way I read this thread it sounds like a guy could do voltage testing on this circuit (120 volt, feed from cat 0 panelboard) "bare handed" as long as they are using an insulated tool, such as a Fluke multimeter and I'm just wanting to make sure I'm 100% clear on that and the reasons why.

I understand (I think) the shock protection line of reasoning. The standard says "avoid contact" and provided one is using an insulated tool they are in compliance with that shock protection requirement. But what about arc flash protection for category 0? Let's say the arc flash boundary is 13 inches. If your hands go inside 13" to do the voltage testing then they would need some level of arc flash hand protection right? What about if the arc flash boundary was 1", would the use of an insulated tool the allows you to keep your hands back further than 1" mean that you do not need any arc flash hand protection?

Thanks again for helping me through these scenarios.


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PostPosted: Fri Apr 13, 2012 4:42 pm 
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racineboxer wrote:
The way I read this thread it sounds like a guy could do voltage testing on this circuit (120 volt, feed from cat 0 panelboard) "bare handed" as long as they are using an insulated tool, such as a Fluke multimeter and I'm just wanting to make sure I'm 100% clear on that and the reasons why


Yes, this is actually called "insulated tools" method. Be careful about the bare hands reference because this is something entirely different. In live line, bare hands methods you actually first move to a floating object position (insulated against both ground and energized line), and then intentionally bond to the line so that you can work on energized lines directly without being insulated. This method is a very specialized work method though. See the following web site for video showing the helicopter variation.

[media=youtube]FrgUZNCkfFI[/media]

Quote:
But what about arc flash protection for category 0? Let's say the arc flash boundary is 13 inches. If your hands go inside 13" to do the voltage testing then they would need some level of arc flash hand protection right? What about if the arc flash boundary was 1", would the use of an insulated tool the allows you to keep your hands back further than 1" mean that you do not need any arc flash hand protection?


100% correct. If you use tools which are long enough that you don't cross the AFB, then there's no PPE requirement for arc flash at least. An example of where this comes in play where I work is that we have some 20 foot telescoping hot sticks. This allows us to reach up to fuse cutouts on a mast and pull the fuses out 20 feet up while being both outside the arc flash boundary and the restricted approach boundary.

Where it gets much more complicated is when you are somewhere in between. Say for instance that you are working on a 24 VDC control power circuit inside a panel which also has a couple 480 V contactors in the same panel. All wiring is built as non-exposed (wires are stripped only to specification). 480 V equipment is calculated as 6 cal/cm^2. This scenario is common in a lot of manufacturing plant controls these days and some machine tool type equipment. It is a bit of a grey area and different people have different conclusions. Obviously no shock protection is necessary, but do you need arc flash protection? In this case since there is no interaction some folks will say no. Others say that just in case to be on the safe side, the answer is yes. Others may say "sometimes"...depending on whether or not there is any reasonable chance of a failure where an energized wire is touching the door but once the door is open, you might be able to dress down. Some also draw a line depending on how far you are away from the 480 V wiring in case you accidentally slip with a tool.


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PostPosted: Fri Apr 13, 2012 6:28 pm 

Joined: Mon Mar 19, 2012 1:21 pm
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Thanks Paul.


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