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OLD_CURMUDGEON
User Rank
Platinum
"HOT" SPOTS
OLD_CURMUDGEON   8/8/2012 12:11:35 PM
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I can vouch for several occurrences of "hot" spots in facilities wiring systems.  The supply voltage surely doesn't have to be in the kilovolt range either.  I've seen dedicated 208/240 (delta / wye) lighting panels explode.  The problem with these panels is NOT ONLY a possible loose lug on the busbars, but also excessive harmonic currents due to the inductive ballasts of large quantities of fluourescent fixtures in place.  These i²r losses can come back to haunt a good lighting load design.

Personally, I've experienced similar scary moments at home.  Since the air handler is situated in the attic crawlspace, separate from the circuit panel, the code requires a disconnect at that location.  One day I happened to be up there inspecting things, when I decided to remove the cover from the 2-circuit circuit breaker disconnect.  Aluminum cable supplied the load (heat strips for wintertime use).  One of the poles of the circuit breaker was blackened due to heat treating because of the oxidation of the aluminum conductor & resultant i²r losses.  The insulation within about 2" of the lug was evaporated.  It was a lucky thing that the electrician dressed the conductors in such a manner that they were not resting on each other, OR there would have been an "interesting" series of phone calls ....... first to the fire department to put out the roof fire, and then to the insurance company for a loss claim.  I was lucky that there was plenty of slack in the supply cable, so I replaced the mini-panel & doused the lugs & conductors with heaping gobs of NO-ALOX, anti-oxidizing compound.  Been fine ever since, and ever year I instruct the A/C service person to check the connections in that disconnect!

 

Rob Spiegel
User Rank
Blogger
Re: FLIR Camera to identify hot spots
Rob Spiegel   8/8/2012 10:59:21 AM
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Carmine, were these infrared pictures sufficient to determine the health of the electrical panels. Or, were they combined with additional inspections?

Island_Al
User Rank
Gold
Re: FLIR Camera to identify hot spots
Island_Al   8/8/2012 9:24:24 AM
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We used an IR camera the same way on a 3 phase 13.8kv line feeding our military facility. At every insulator on the 1/2 mile run, I had a guy take a monthly photograph. We were working next to the ocean and salt residue would build up on the insulators decreasing the resistance, causing heat, and eventually burn through. Fixing these was a nasty job and we had to post a guard at the power transfer switch. But using the camera, most of the time we would kill the power and simply clean the insulator using a pressure washer. It would seem like insulators are perfect, but a few meg ohm resistance (cable insulation/insulator) could have knocked the site off line for days. Nasty stuff that HV power is. I hate it. Explains why I love TTL so much.

Carmine
User Rank
Iron
Re: FLIR Camera to identify hot spots
Carmine   8/7/2012 3:45:54 PM
At regular intervals (I think it was yearly) a PM task for Panel Imaging would be created.  The contractors would be contacted and would come and take Infrared pictures of all the Electrical panels (including panels containing control circuitry such as motor drives and PLCs). 

They would then visually analyze these pictures to locate any "hot spots"  These hot spots could be caused by a loose connection that just needed to be tightened or a failing component, etc.

TJ McDermott
User Rank
Blogger
Re: Another loose connection
TJ McDermott   8/7/2012 3:38:02 PM
NO RATINGS
Checking the torque of electrical terminations is a normal part of scheduled electrical maintenance of industrial machinery.  I don't know that I would check every low voltage connection, all of the high voltage connections (those that could likely heat up by being loose) should be.

 

Rob Spiegel
User Rank
Blogger
Re: FLIR Camera to identify hot spots
Rob Spiegel   8/7/2012 3:34:36 PM
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So I take it, Carmine, that the program was successful at identifying faulty panels. How exactly did it work?

Carmine
User Rank
Iron
FLIR Camera to identify hot spots
Carmine   8/7/2012 10:00:20 AM
NO RATINGS
Years ago I worked for a company that contracted a service to image each electrical panel in the plant with a FLIR camera. This process was part of their Preventative Maintenance (PM) program and was designed to identify these types of failures before they interrupted production. FLIR camera prices have fallen over the years making this type of PM much more affordable.

naperlou
User Rank
Blogger
Another loose connection
naperlou   8/7/2012 9:01:09 AM
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Happens all the time.  There have been numerous articles on this site about such situations.  I know I have "fixed" plenty of problems where it was just a loose wire.  It is tragic that someone was killed by the circuit breaker situation.  Repeatedly doing the same thing is inviting a problem.  Thankfully, it is not usually so deadly.

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