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 Post subject: Infrared thermography and arc flash hazard.
PostPosted: Tue May 05, 2015 8:47 am 

Joined: Tue May 05, 2015 8:31 am
Posts: 3
I do work at a plant that has a lot "Beyond Category Hazard Switchgear". Our work in this switchgear is restricted to dead work only.
They also hire us to accompany the person doing thermography accessment. This guy wants these panels opened, i refused based on the "No energized work " restriction.
Is there some rule that would allow this.
This equipment has not been serviced or maintained.
Chet


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 Post subject: Re: Infrared thermography and arc flash hazard.
PostPosted: Tue May 05, 2015 8:58 am 
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Joined: Tue Jan 19, 2010 2:35 pm
Posts: 132
I agree with you, it's not safe, (even wearing category 4 PPE) to open up a board or panel that's above 40 calories. And what's the arc flash boundary listed on the gear? It could be well over 20 or more feet. If you remove a bolt or screw from the gear, I'd say it's not considered closed or safe. Good luck,


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 Post subject: Re: Infrared thermography and arc flash hazard.
PostPosted: Tue May 05, 2015 9:34 am 
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Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
Equipment that has been properly installed and maintained does not pose an arc flash hazard if you are doing work that is not interacting with the equipment in a way which would cause an arc to occur. That's in the definition of "arc flash hazard" in 70E. This has nothing to do with the hazard itself.

By way of example, let's just consider being struck by lightning. People can and have been struck by lightning even on a clear sunny day with no clouds around. This does not mean that playing golf on a clear, sunny day with no clouds is inherently dangerous because the likelihood of being struck by lightning without a thunderstorm nearby is very low.

Similarly even if the arc flash hazard is so great that serious injury or death is certain if one to occur, if the likelihood of its occurrence while performing a particular task is very low, then PPE is not required. So we can do SOME work with equipment even if PPE is not available. For the IR scan itself, there is no interaction with equipment and you can stand outside the restricted approach boundary so there is no interaction to be concerned with. That leaves opening and closing doors. You have to consider the design and condition of the equipment in that regard. For instance if cables were improperly installed to where they are stuffed in the cabinets and can be pinched in the doors, or if there are electrically conductive dusts or liquids laying on the cabinet that can enter while opening and closing doors, then the act of opening or closing a door would be considered interacting in a way that can cause an arc. Otherwise, it's not.

Furthermore, this question has to be taken seriously at a management level for two reasons. There are roughly 3 ways to test for loose connections and loose connections are a very common cause of arc flash. The first way is using an IR scan but this must be done while energized. The second way is using milliohm meters but these are fraught with all kinds of issues with reliable testing issues. The third method is torque testing but the latter flies in the face of basic mechanical engineering and has gone from a recommended practice to a practice which is considered poor practice. Only the latter two can be done offline though so generally you are stuck with milliohm testing if you can't do IR scans, which is considered the best method.

All maintenance standards for "properly maintaining" equipment specify IR scans. Not doing them is not properly maintaining equipment. So the risk of an arc flash is increased by not doing IR scans for all tasks other than the IR scan itself, which is in itself a relatively low risk task since no direct interaction with equipment occurs. So refusing to do an IR scan because of a concern over the risk of doing it increases the risk for everything else.

Also, improper maintenance makes the whole incident energy calculation pure garbage because the reliability of the overcurrent protection devices becomes an issue. So if you don't maintain it, then don't bother putting arc flash stickers on it no matter what the value is because they're meaningless anyways.


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 Post subject: Re: Infrared thermography and arc flash hazard.
PostPosted: Wed May 06, 2015 8:43 am 
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Joined: Tue Jan 13, 2009 5:00 pm
Posts: 524
I would consider opening any bolted door that might fall inward to be a possible interaction. Hinged doors with hinges in good shape would be an exception. Might want to consider installing thermography windows while you're at it.


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 Post subject: Re: Infrared thermography and arc flash hazard.
PostPosted: Sat May 09, 2015 4:41 pm 

Joined: Tue May 05, 2015 8:31 am
Posts: 3
Thanks for the replies. We did the IR check, found a problem and were able to repair it with an outage today.


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 Post subject: Re: Infrared thermography and arc flash hazard.
PostPosted: Mon May 11, 2015 4:57 am 

Joined: Mon Jun 09, 2014 9:19 am
Posts: 43
I agree with Stevenal, if you are performing an Infrared Scan you are interacting with the equipment that could cause an arc flash. I was performing a scan several years ago on 4160v equipment. The tech that was helping me and I were taking the covers off the back of a panel and we dropped the cover into the equipment. it narrowly missed the energized bus, and we both messed ourselves because we thought we blew the equipment up. Fortunately it turned out ok, there was no flash, but that doesn't mean it won't happen the next time.
I would seriously consider installing infrared windows, but only after you have had the installation engineered so you know where to install them correctly.
Thanks!


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 Post subject: Re: Infrared thermography and arc flash hazard.
PostPosted: Mon May 11, 2015 5:58 am 
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Joined: Sat Feb 07, 2009 9:24 am
Posts: 32
Location: Swanton, Vermont
I've been conducting IR inspections for the past 15 years. First working as an electrician/escort removing covers and taking measurements and the past 12 years as thermographer. Removing bolted covers of equipment with an arc energy value over 1.2 cal/cm² are not usually done. An example where it may be done is a motor splice box where it is known that the splices are insulated and are not stuffed into the enclosure.
Hinged covers are usually considered of little risk and can be opened safely using a
thoughtful protocol. With equipment calculated to have higher than 1.2 cal energy the proper PPE is worn while the cover is opened. Often there will be a number of enclosures to inspect. The electrician will remove all but one or two fasteners and then don the rated PPE to remove the final fastener and open the cover. I will then approach the enclosure and scan the equipment. My standards work clothing is 12 calorie rated but I do not ordinarily were a face shield etc. while scanning gear. When the scan is complete I will retreat from the arc flash boundary and the electrician will take any required measurements, close the doors and apply one or two fasteners while wearing the required level of PPE. Then, they remove the PPE and finish with the rest of the fasteners.

Infrared windows.
Often I've found where IR windows were purchased by management and installed with no input from the maintenance dept. or the thermographer. This hardly ever works out well. Window materials must be compatible with the imager. They are not all the same. The window must transmit IR radiation in the same wavelength as the imager used. The costs of the materials vary widely and some materials have to be selected for the environment. So that you don't want to pay for a material for hundreds of windows that is not necessary nor do you want to purchase ones that will not stand up to the conditions. Window size is important as is placement. Manufacturers or often optimistic in their field of view specifications and I find that often I can not 'see' or take temperature measurements but a small percentage of the area need. But the specifications would show otherwise. Basically you have to put the imager lens straight on to the window to get adequate results. A wide angle lens is necessary for this to work in most enclosures. My advice would to always consult with the maintenance and thermography persons and to try a single application before going forward and fitting up a large number of IR windows.

This is my personal experience and it may or may not comply with your facility safety protocols.


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 Post subject: Re: Infrared thermography and arc flash hazard.
PostPosted: Mon May 11, 2015 8:11 am 
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Joined: Mon Jun 07, 2010 9:40 am
Posts: 119
Actually it is technologlically possible to do resistance checks while energized. My company developed a system to do just that for one client.
[A data center client] You wouldnn't finde me touching it with the proverbial 10' pole. [Actually it uses ~4' poles] I don't think even that client calls for it any more. I don't see where the benefit was ever worth the risk.


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 Post subject: Re: Infrared thermography and arc flash hazard.
PostPosted: Fri May 15, 2015 4:29 pm 
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Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
Not only technologically possible but its almost the definition of a shunt for DC work. However as stated it is tricky to do and get it right on a live circuit.


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