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 Post subject: Insulated Gloves when metering 120V industrial control circuits
PostPosted: Mon May 06, 2013 7:16 am 
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Hey guys, I imagine this topic has been beat like a dead horse...but at the end of the day I don't have a clear answer in my mind. Currently we are deciding this at our industrial facility. We currently wear insulated Class 0 gloves with leathers to meter anything above 300V (including 277V). However, for circuits below 240V we currently do not wear insulated gloves for metering using the standard Fluke 87V.

I'm aware the infamous table states the RAB to "avoid contact", which causes much confusion and debate. I want some honest experiences with industrial control facilities. What are you electricians, technicians and engineers doing? As an electrician turned electrical engineer, I value being practical and realize that troubleshooting 120V circuits in a control panel is just about impossible while taking gloves off and on every other voltage reading. But at the same time I want to place safety at the forefront. Thanks in advance for any input.

RonD


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PostPosted: Tue May 07, 2013 7:02 pm 
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IEEE 516 is the most widely recognized standard for this. 70e, section 130.4 could not be more vague with regards to viable work methods and really provides no clear guidance. If you are using insulated tool work method (meter probes), then you don't need gloves. If you are a glove fanatic then at 69 kv, realize there is no available glove.


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PostPosted: Wed May 08, 2013 6:12 am 
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My plant requires class 0 gloves when using meters in panels that have greater than 50V anywhere in the panel. We have been doing this since 2007. Most of our control panels have 24VDC through 480VAC. We also have over 100 multi-skilled craftsmen troubleshooting inside panels. Human nature would tempt some in the population of troubleshooters to not put their gloves on when the testing moved through a certain threshold of voltage. Unfortunately our safety policies tend to be conservative in order to protect the least knowledgeable or the overconfident employee from getting injured. It is just plant easier to enforce a blanket rule based on worst case panel voltage than a sometimes you do sometime you don't policy with our large population.

I have not had anyone ask me to reduce the PPE required to measure 240V and below since the policy was implemented. I am interested in what you come up with at your plant.


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PostPosted: Wed May 08, 2013 7:05 am 
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Paul, thanks for the info. I've browsed through IEEE 516 and it appears it deals mainly with voltages at the transmission level...I don't see anything for low voltage? You refer to the insulated tool method, and this allows a worker to meter 120V without gloves?

App NC, we only allow qualified electrical workers to meter the voltage inside a control panel. I imagine there would be other hazards letting unqualified workers inside these cabinets, but each location is unique. In our case, we meter 120V control circuits for the purpose of troubleshooting or testing...in some cases this may last several hours. Keep in mind these are in PLC panels with din rail mount terminal blocks, usually 6mm wide, and can involve potentially hundreds of readings through a session. Wearing class 0 insulated gloves and leather overs for measuring voltage on a fused 3A 120V control circuit in this instance seems quite insane. I'd go so far to say that wearing them in this instance actually creates more hazards than it may mitigate.

In my opinion, it's impossible to compare a 3A non-delay fused 120V control circuit to a 60A thermal breaker 120V distribution circuit. I understand we're talking about shock here and not arc flash, but these types of factors must be considered when applying rules. I'm not a fan of blanket rules, they tend to set up people for failure and are often times a way of avoiding the nitty gritty details that should be discussed. Checking voltage in a 120/240V breaker panel I'd have no issues with insulated gloves, but in a control or PLC panel...I'm skeptical.


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PostPosted: Wed May 08, 2013 3:35 pm 
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RonD,
I do not want to promote that multi-skilled = unqualified. Our multi-skilled craftsmen are trained per 70E for the electrical tasks they are expected to perform.

My plant has a pro glove mindset. We wear cut resistant gloves for most mechanical tasks and electrical gloves for most takes in a panel (other than operating finger safe devices or connecting processor communication cables). I have been involved in many lengthy troubleshooting situations; I wear thin cotton liners under the rubber gloves when long term use is expected. Touching meter leads to terminal blocks does not require a high level of dexterity. Our policies are trying to prevent the fluke combination of inadvertent movement and exposed contacts in an environment where most contacts are not finger safe. If our gear was mostly of a modern finger safe design I would push for a different policy. The statistics below have been quoted in many locations. I have personally been shocked above the let go threshold when I was a teenager and do not wish to push my luck again.

[color=#141414][font=Tahoma][color=#141414][font=Tahoma]I do not think PPE for 3amps sounds insane at all[/font][/color][/font][/color]

50 to 150 mA
The victim gets an extremely painful shock.
The [font=Tahoma]breathing stops (respiratory arrest).[/font]
Severe muscle contraction: flexor muscles may cause holding on, extensor muscles may cause intense pushing away.
Death is possible.
([font=Tahoma]At 75 mA and above – The victim undergoes ventricular fibrillation (very rapid, ineffective heartbeat). This condition can cause death within a few minutes. The only way to save the victim is by a special device called defibrillator.)[/font]

[font=Tahoma]1 A and above[/font]
Uneven heartbeats occurs (Ventricular fibrillation).The muscles will contract.
Damage to the nerves.
Death is likely.
http://lee65.hubpages.com/hub/Electric-Shock-Injuries

http://ecmweb.com/content/basics-electric-shock


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PostPosted: Wed May 08, 2013 8:15 pm 
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The quoted information about physiological effects is incorrect most of the time. The table has been widely published with varying information. The problem is that the voltage, current, and time all play a role. The definitive source although more recent work has refined some of it is Dalziel. IEEE 80 contains much more info. A basic design principle in many resistance grounded systems as well as substation grounding is to maintain conditions where there is not enough current or more specifically energy to exceed the fibrillation threshold. As an example, a contractor at my site unlocked a 4160 v contactor to test it, went to lunch, forgot to reinstall the lock, and received a shock while attempting to remove a ground and his arm brushed a PT in the same compartment. The resistance ground worked and the relay tripped nearly immediately. He walked away with minor welts near the two points of contact and no long term injury. If it had been phase to phase, it would have been around 4 A and most of the voltage drop across the electrician, before magnetically launching his corpse from the equipment.

IEEE 516 does look like "high voltage" but the approach distance tables in OSHA, 70E, and NESC come from that standard. It lays out about 7 or 8 work methods. 70E mentions them in 130.4 but doesn't give any explanation on how they work. If you get IEEE 516, get the newer version. The old versions especially prior to 2009 have some math errors and incorrect approach distances although it only matters over 25 kv.


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PostPosted: Tue May 14, 2013 10:53 am 
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There is a rubber glove "slightly" thinner than a Class 0 which is usable UP TO 500 volts a/c or 750 volts dc. This is Class 00. For user comfort, I suggest Type 1 over Type 2. I will ALWAYS endorse the use of insulating gloves & protectors. In a humid environment, I have personally witnessed current tracking to an individual who was not touching the source, but close enough for the current to "jump". Humidity obviously is a factor involved with how far this "jump" will occur.

Although I endorse the use of PPE; by using a thinner glove and using Natural Rubber over Synthetic, this WILL enhance hand dexterity resulting in a more comfortable working environment.


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PostPosted: Tue May 14, 2013 11:09 am 
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Greg Cain wrote:
There is a rubber glove "slightly" thinner than a Class 0 which is usable UP TO 500 volts a/c or 750 volts dc. This is Class 00. For user comfort, I suggest Type 1 over Type 2. I will ALWAYS endorse the use of insulating gloves & protectors. In a humid environment, I have personally witnessed current tracking to an individual who was not touching the source, but close enough for the current to "jump". Humidity obviously is a factor involved with how far this "jump" will occur.

Although I endorse the use of PPE; by using a thinner glove and using Natural Rubber over Synthetic, this WILL enhance hand dexterity resulting in a more comfortable working environment.


The current tracked through the insulated meter probes? :confused: Keep in mind these are "finger safe" terminal blocks.


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PostPosted: Fri Aug 16, 2013 6:14 pm 
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Greg Cain wrote:
There is a rubber glove "slightly" thinner than a Class 0 which is usable UP TO 500 volts a/c or 750 volts dc. This is Class 00. For user comfort, I suggest Type 1 over Type 2. I will ALWAYS endorse the use of insulating gloves & protectors. In a humid environment, I have personally witnessed current tracking to an individual who was not touching the source, but close enough for the current to "jump". Humidity obviously is a factor involved with how far this "jump" will occur.

Although I endorse the use of PPE; by using a thinner glove and using Natural Rubber over Synthetic, this WILL enhance hand dexterity resulting in a more comfortable working environment.


Umm, huh? I don't believe it one bit. The test that the glove companies do is that the glove is filled with water to a specified depth and then immersed in a tank of water, and then essentially hi potted from the water inside the glove to the outside. You cannot possibly get any more saturated with water than this. With insulated tools that are tested, nearly the same method is used. The tool is spritzed with water and hi potted at intervals along the entire length of the tool to verify that it is effective up to 100 kV per foot. Now one major reason that this is done...do linemen get called out to work on utility distribution systems on bright sunny days or on the darkest, wettest days with lightning coming down everywhere? Yep, the stuff has to work while soaked with rain water.

That is not to say that you can't receive a shock. In fact, IEEE 516 even documents the fact that shock protection PPE is specifically DESIGNED to operate with a small amount of current passing through the user. That is one of the major reasons for avoiding "doubly protected" conditions such as wearing dielectric overboots AND gloves...because the line worker then becomes a floating object and all other objects in the vicinity whether grounded or at line voltage are at a much different voltage potential relative to the line worker. The goal as with all equipment designed for utility use is to avoid LETHAL conditions.


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