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 Post subject: Rubber gloves vs. Arc flash clothing
PostPosted: Fri Jul 23, 2010 3:17 pm 
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I have a question for the forum, I searched some and found nothing on this issue.
Looking at worker safety rules working on energized equipment, gloving to be specific, we are always told to use the highest voltage available, and protect ourselves.

Does this apply to amperage as well?


An exagerated example, gloving 3 phase, unisulated energized bus bars in a network system, at 480v, you must wear rubber gloves rated at 480v. If you cover two phases and work one 277v phase, you cannot wear 300v gloves, you must wear 480v gloves.
So if a worker is gloving a 30,000 amp uninsulated bus, the worker must wear arc flash clothing for that rating. If the workers covers two phases, with rubber blankets, with intent to work on one phase, does this now reduce the available amperage to say 10,000 amps, and reduce the arc flash rating on the clothing a worker must wear?

In other words, you cannot reduce the voltage by covering up, so can you legally reduce the amperage by covering up?


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PostPosted: Sun Jul 25, 2010 9:51 am 
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hurricane harry wrote:
I have a question for the forum, I searched some and found nothing on this issue.
Looking at worker safety rules working on energized equipment, gloving to be specific, we are always told to use the highest voltage available, and protect ourselves.

Does this apply to amperage as well?


An exagerated example, gloving 3 phase, unisulated energized bus bars in a network system, at 480v, you must wear rubber gloves rated at 480v. If you cover two phases and work one 277v phase, you cannot wear 300v gloves, you must wear 480v gloves.
So if a worker is gloving a 30,000 amp uninsulated bus, the worker must wear arc flash clothing for that rating. If the workers covers two phases, with rubber blankets, with intent to work on one phase, does this now reduce the available amperage to say 10,000 amps, and reduce the arc flash rating on the clothing a worker must wear?

In other words, you cannot reduce the voltage by covering up, so can you legally reduce the amperage by covering up?


Great Question. Unfortunately I am probably not giving the answer you will want to hear. The arc rated clothing is rated in calories/cm^2 which must exceed the prospective incident energy from an arc flash. This energy is based on both short circuit current, arc duration, and a few other variables.

Covering up one or more phases does not reduce the short circuit current that could flow if a fault occured since the current is limited by the impedance of the conductor and everything back towards the source - transformers, feeders, utility systems etc. The blanketing is intended to reduce exposure to electric shock but the arc flash hazard techincally still exists based on NFPA's definition which includes "interacting" with the equipment (bus). If the blanket failed during an arc flash, the short circuit current still exists on all three phases.

Hope it helps and let me know if you have any other questions.

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PostPosted: Wed Jan 19, 2011 10:18 am 
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Insulating blanket increases working distance?

Can the blanket be used to increase your working distance? If I'm working at a location, not working on energized conductors, but standing near energized conductors... and I use an insulating blanket on the energized conductors close to me, can I now consider that either the energized conductors are now not exposed or that I have increased my working distance from the energized conductors or the possible arcing point? My thinking is this... if I was 24 inches from the energized bus, and I now use a 48" insulating blanket on the energized bus, have I not increased my working distance?


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PostPosted: Thu Jan 20, 2011 11:36 am 
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I would probably say yes, you have installed a temporary barrier that helps prevent contact.
But if you were to comprimise that barrier in some way, you still have all the amperage available of the initail arc.


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PostPosted: Fri Jan 21, 2011 6:00 am 
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It depends on site's PPE Matrix. For us a Class 1 rated gloves are the MINIMUM for all live work - from installing a breaker in a panel (that has a rating of .2 cals) or taking amperage readings on a motor feeder.

The best way I have found to minimize the Arc Flash rating is to de-energize the equipment, verify it and work on it with leather gloves...

Prime example of taking Arc Flash to the extreme... The client I work with primarily went out and bought 2 sets of insulated (1 kv) tools COMPLETE... I asked "What for??" They said "So that when you need to retorque the main lugs and bus bars in a 208 volt or 480 volt piece of equipment you can do it LIVE." I said "I can't change a light bulb out here without a 6 page work permit, and you expect that doing this kind of live work will be easier and with less paperwork? Why not do a shutdown and do it with the Main Source locked out?" The tools have never been used and are still in plastic....


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PostPosted: Fri Jan 21, 2011 7:19 am 
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People seem to think the 70E is some sort of guide for doing energized work, it's primary intent is to promote not working energized. You think EEWP's are a pain in the rear by accident?


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PostPosted: Fri Jan 21, 2011 2:01 pm 
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In our area, we work on a network grid. The grid remains energized all of the time. We also have spot networks built in highrise vaults, they too are to remain energized all of the time, or the building loses all power. This can be unacceptable for some businesses such as server farms, laboratories, and security sources. We work on energized conductors every single day. Taking outages for the purpose of working de-energized is not really an option for us.


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PostPosted: Sat Jan 22, 2011 7:05 am 
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hurricane harry wrote:
In our area, downtown Seattle, we work on a network grid. The grid remains energized all of the time. We also have spot networks built in highrise vaults, they too are to remain energized all of the time, or the building loses all power. This can be unacceptable for some businesses such as server farms, laboratories, and security sources. We work on energized conductors every single day. Taking outages for the purpose of working de-energized is not really an option for us.


I hear that all the time, and granted there are some exceptions, but I do outages at server farms, labs, military complexes, nuclear plants, etc all the time, it justs takes a little more coordination.

If you think the reason for not de-energizing will be agreed on by a jury after someone gets injured or killed then you can probally justify it. Then you need to do a risk analysis including an Incident Energy calulation for what you are working on. Your example in your OP greatly exceeds the limits of the 70E tables so a calulation is required, and with a 30,000A bus I highly doubt there is any PPE that can protect you if an arc flash were to occur.


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PostPosted: Sat Jan 22, 2011 8:47 am 
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After doing an Arc Flash study, the client I work with noticed several sites that exceeded their limit of safe work (35 cal/cm2). Some were approaching 50 in the sites I work at. They did some work and with some setting changes lowerred it to a safer level to work at (<10 cal/cm2)..

Granted this is not possible everywhere but as stated before, if you are going to be working on LIVE systems with extremely high Arc Flash ratings, you best make sure your PPE and safety measures are at their highest, or plan an outtage.. Everything can be shutdown, it is just a matter of how much coordinating it takes...


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PostPosted: Mon Jan 24, 2011 8:24 am 
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Zog wrote:
I hear that all the time, and granted there are some exceptions, but I do outages at server farms, labs, military complexes, nuclear plants, etc all the time, it justs takes a little more coordination.

If you think the reason for not de-energizing will be agreed on by a jury after someone gets injured or killed then you can probally justify it. Then you need to do a risk analysis including an Incident Energy calulation for what you are working on. Your example in your OP greatly exceeds the limits of the 70E tables so a calulation is required, and with a 30,000A bus I highly doubt there is any PPE that can protect you if an arc flash were to occur.


I disagree. Lineman work on energized conductors everday, you just don't know it. If they took outages everytime, your lights would be out constantly.
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PostPosted: Mon Jan 24, 2011 12:41 pm 
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hurricane harry wrote:
I disagree. Lineman work on energized conductors everday, you just don't know it. If they took outages everytime, your lights would be out constantly.


I know what linemen do, they recicve special training for live bare hand work, they do nto fall under the 70E, they fall under the NESC which has different requirements and is changing right now to incorperate some of the 70E's arc flash requirements.

Conductors in open air are very different animals than bus in a vault when it comes to arc flash.

I am sorry you do not like the answers you have been given here, which are all correct. Your OP shows a gross misunderstanding of arc flash requirements, you may want to listen and learn rather than try to justify your case. Or call OSHA and ask them.


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PostPosted: Mon Jan 24, 2011 1:02 pm 
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Zog wrote:
I know what linemen do, they recicve special training for live bare hand work, they do nto fall under the 70E, they fall under the NESC which has different requirements and is changing right now to incorperate some of the 70E's arc flash requirements.

Conductors in open air are very different animals than bus in a vault when it comes to arc flash.

I am sorry you do not like the answers you have been given here, which are all correct. [color="Red"]Your OP shows a gross misunderstanding of arc flash requirements,[/color] you may want to listen and learn rather than try to justify your case. Or call OSHA and ask them.


Yes you are correct, I have no idea what requirements are neccesary.
From what I am seeing on this forum, most posters are engineers or management personel. Perhaps you should try and learn from field personel on real work conditions, not what is percieved in some laboratory.


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PostPosted: Mon Jan 24, 2011 2:03 pm 
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hurricane harry wrote:
Yes you are correct, I have no idea what requirements are neccesary.
From what I am seeing on this forum, most posters are engineers or management personel. Perhaps you should try and learn from field personel on real work conditions, not what is percieved in some laboratory.


I spent 15 years in the field testing power systems, other members here have more experience than that. There are IEEE 1584 and NFPA 70E commitee members here as well. I don't know what else to tell you besides that electrical safety requirements have been changing over the last few years, and OSHA is agressively enforcing the new regulations.


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PostPosted: Mon Jan 24, 2011 2:48 pm 
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The daily grind, everyday.
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PostPosted: Mon Jan 24, 2011 5:35 pm 
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Cute, is that all you wear for arc flash PPE? Has an arc flash study been done on that equipment? IF you insist on working live at least make an attempt to wear the correct PPE.


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PostPosted: Mon Jan 24, 2011 6:07 pm 
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Thank you for your concern. No, we are not rogue bands of cable splicers roaming the streets. You stated in your previous post that lineman are not yet nfpa, and that is wear we are. We do have 40 cal suits. We do have our flash calculations. The reason I started this thread was to point out that there are some variations to the way things are calculated and methods being used that do not quite work in our end of the industry.


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PostPosted: Thu Jan 27, 2011 6:19 am 
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You think for arc flash hazards , what should linesman doing?


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PostPosted: Tue Jan 17, 2012 3:49 pm 
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Arc Flash and Amperage

You really can't reduce the amperage but there are two things you can do from an arc flash perspective. Don't use NFPA 70E for linework. NESC is what applies. When doing very high voltage work it is rare to have an arc flash especially when doing transmission level live work. Use the hazard assessment tools like ArcPro (what I used to do the calculations in the NESC tables) and look at work practices. You are right, this work is most often done live and pretty much has to be. The NESC does allow you to not use the full arc rating IF the hazard is increased by the PPE. This is often called the "heat stress clause" but is more applicable to barehand work. The key is a detailed, job specific hazard assessment by a qualified team and quality work procedures and specific job briefing covering the actual scope of the work. I always recommend line workers wear arc rated clothing and it is better in higher voltages to wear arc rated t-shirts in case of a "tracking arc" which often occurs when contacting medium or high voltage (which "should" never happen but does from time to time).

Wearing an arc rated t-shirt will often make the upper torso near 20 cal protection and arc rated jeans can do the same for the lower torso. That is pretty close to the energy on most Transmission systems due to the quick clearing times. The real issue in one of these arc events is that you can be "in the arc" so the arc rated gear level may not be as important as having on ONLY arc rated gear. Let me know if I can assist further. I do arc flash testing and PPE consulting. I don't sell PPE though.


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PostPosted: Wed Jan 18, 2012 9:43 am 
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hurricane harry wrote:
Thank you for your concern. No, we are not rogue bands of cable splicers roaming the streets. You stated in your previous post that lineman are not yet nfpa, and that is wear we are. We do have 40 cal suits. We do have our flash calculations. The reason I started this thread was to point out that there are some variations to the way things are calculated and methods being used that do not quite work in our end of the industry.


Hurricane Harry-I come from the private industry from operations and a safety standpoint. I now work in consulting and TVA is one of our clients. We plan very strategically with them for electrical work that HAS to be done live and what can be done during outages. They do have to work on circuits live BUT they also do A LOT of electrical work during outages. Obviously we see that 70E doesn't apply to the type of work you are mentioning in this post but I do agree with others that when 70E is applicable, that if you think-while sitting on the witness stand-that you can whole hearted say in front of victims families and a jury that we HAD to do this work live-then you have no worries my friend!


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