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TitleByPosted On cowboy&dishwasher 9/1/2006
I need other opinions. This disconnect is on a buss. The owner checked it with a spot thermometerand read 90 deg. F. and thinks it is OK. To me there is a problem. What do ya'll think? Carl M 9/1/2006
In my experience, the heat shown in infrared images of fuse/switch/bus equipment in good condition would show maximum temperature rise across the fuses. Switch and bus stab assemblies should not show as much heat rise as the fuse and generally be the same temperature as the conductors. Pete 9/6/2006
To me your image is indicating a possible galled or loose termination, or a high resistance connection at the stab assembly. I would not blow this off as satisfactory. Ask the client what the spot ratio of their spot radiometer is and how far away they were. I am not really buying into the whole 90 degf. story, from the client, after looking at your image. In this case, it is not what one temperature tells you. It is what the overall comparision of all the phases tells you. In this case it tells me more investigation would be a proactive approach to maintenance.

For phase to phase comparisions, with balanced current contitions, or like for like devices we use the following critera for observed thermal anomalies at our plant:

20 degf. delta: initial concern.
40 degf. delta: increased inspection frequency.
>60 degf. delta: immediate corrective action.

We have seen these conditions on some disconnects at our plant. After maintenance has been performed the noted thermal anomalies have been corrected. As they say " An ounce of prevention is worth a pound of cure". Just my two cwnts worth.

Pete jvoitl 9/6/2006
See my article about IR thermometers in the June 2006 ITC newsletter. Also, by the looks of your image, the hottest spot is on a metal part of the disconnect. This probably has low emissivity, and thus is even hotter than your camera shows Laland 9/8/2006
can you post a photo for the image. cowboy&dishwasher 9/11/2006
Here's the photo Laland requested. Gord 10/4/2006
In my opinion, you have a loose clip on the "B" phase stab on the back of this disconnect. These stabs have a spring like clip on the sides of the stab that keep it tightr on the buss. After some heat these little stabs and springs get weak and the tension decreases.
Poor switch contact testtech 10/4/2006
The blade is making poor poor contact with the fixed contact. Exercise the switch and the problem will be gone. Alternatively, take a non-conducting tool (I use a plastic chop stick.) and tap the switch arm in. It will move a bit and the heating will disappear. (Of course this last move will probably violate NFPA 70E, but it will fix the problem.) nelly 10/4/2006
As i have seen on the image im sure that a problem exist on the center phase of the switch particularly at the blade contact and the pivot joint. The image didnt really show which were hotter between the two.If the blade contact was the problen you can recommend to clean the contacts but if the pivot joint tell the customer to replace the switch. chas2600 10/5/2006
Be safe replace the switch. B phase has a problem. who 10/6/2006
In my opion you just have a emissisivity problem. If you look closser what apears as a hot spot is actuly your reflection on the screw by the thermale conecction and from the side of thermal by otherscrew. It is not uncommone to get a braker back from maintanance this way, just trend it. kfs 10/7/2006
What's the rating of the disconnect & what was the laoding per phase during the inspection? Laland 10/8/2006
Hello cowboy&dishwasher. My opinion is that there is a problem on the B-phase. I am not familiar with the mechanism beneath but am pretty sure that there is a problem because there is heat conduction down to the fuse end. Looking at phase A and B, they are cold.If you have so have located and solve the problem, please share it with us. Geoff 10/10/2006
Tell the owner of this disconnect, that if He does not atleast remove and service this switch, better yet replace the switch, He will very shortly be replacing it and a section of BUSS. Pete 10/11/2006

I have a bit of concern with your reply to this issue. How can you say it is the Thermographers reflection? If it was the Thermographer reflection he has bigger problems than the disconnect. I don't think that even if the Emissivity was way off base the hot spot would not be from the Thermographer. According to you his body temperature is over 109 degf. Sure hope he recovered from that fever. Please explain your reasoning to me, apparently I am not understanding your view point. kfs 10/11/2006
That's not a reflection but I would be interested to know if the load is balanced acroos the phases. jvoitl 10/12/2006
I have found numerous disconnects like this and it has always been the stab assembly. If the load were unbalanced, especially this much, the wires on the left would show a temperature differece too. kfs 10/12/2006

Good point regarding the surface temperature of the cables. I'm a utility engineer based in the UK - what do you mean by the 'stab assembly'? Pete 10/12/2006
At our plant we refer to a "Stab Assembly" as the section of the disconnect where the movable contacts connect to the female stationary contacts. Or on most molded case circuit breakers where the stabs on the breaker connect to the buss. I hope this helps if not, e-mail me and I will try until I get it right.


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