Message Board Thread - "evaluate hot crimp on control wire"

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evaluate hot crimp on control wire electricpete 9/27/2004
I am brand new to thermography and brand new to this forum. Attached is a picture of a hot-spot we are watching. Particularly interested in box#3 (left side of image) based on its position within the circuit. It started at 11C rise, went to 0C rise (above ambient marked B) for a few measurements, now bouncing aroudn 7-9C rise. We have not measured the current, but we don't think there was any significant decrease when it went to 0.

By the way, these are fused disconnects in a 125vdc control circuit, and the hot-spot is on a lug associated with the wire connected to the fuse disconnect. In fact I believe there are 2 lugs landed on that point, and based on the thermal image, the one in front is not the hot one (the hotter one is not directly visible to the camera). This conclusion based on looking at the hot wire that comes out.

Our approach is to use 0.95 emissivity for the whole image. There is a relay to the left producing heat which elevates the background behind the point of concern. No special background compensation was applied and we compare to ambient located at a cooler part of the cabinet. Any coments on this approach?

My main questions:
1 - How would you rank the severity of this?
2 - What standards are available for evaluating electrical hot-spots.
3 - Is anyone aware of similar crimped connections that were failed which had thermal history available? i.e. we are interested to get some basis for answering the question: when would it fail? Have other crimps failed rapidly after showing similar rises (noting the erratic behavior?).
Thanks for bearing with my long question and looking forward to any commnents.



 
Re:evaluate hot crimp on control wire Manuel 9/27/2004
hi there ..
welcome to this forums.

let me tell you that we saw a temperature difference there but is not a real problem due image shows temp max at Point 3 of 38C..
do you know how much warmer is your hand?..maybe 35 to 36 C.

personally i find no problems at this image.

if you can take a certificacion i course you will learn little more sharp details on this tricky situations.

regards.

roberto cruz
thermoimagen
 
Re:evaluate hot crimp on control wire pktsgt 9/28/2004
Hello and Welcome,

Have to agree with the above. I can not see a problem with is picture. I'm a Level III Thermographer(and an electrician) I suggest strongly you take a certified class.

Kat
 
Re:evaluate hot crimp on control wire electricpete 9/28/2004
Thanks. I am planning on taking a class. I personally did not see it as a big problem either but it is a very critical location and still there are some questions:

2 - What standards are available for evaluating electrical hot-spots.
3 - Is anyone aware of similar crimped connections that were failed which had thermal history available? i.e. are there any data points to connect temperature rise, absolute temperature, or erratic behavior with constant load to actual failure?
 
Re:evaluate hot crimp on control wire Bob Berry 9/28/2004
Hi Pete,

I would like to point out that that the measured and projected / normalised temperature rises and severity classifaction must be viewed along with type of equipment, cruciality to operation, and the process that the equipment operates under to truly assess the severity of the problem. It is important to understand that a piece of equipment may fail at any stage , not just at a critical level. For this reason no accurate timeline can generally be created to predict electrical failure.

If this lug is as you said on a critical piece of equipment, then it might be worth keeping an eye on it. I dont think that you should lose too much sleep over it, but schedule regular inspections until you have more information and most importantly take current readings sooner rather than later.

In answer to your questions regarding standards and severity, most of this is covered in Level 1 and 2 courses.
 
Re:evaluate hot crimp on control wire electricpete 9/28/2004
Yes - I agree a course would be good and plan to take one. I still need to try to understand as best as I can in the meantime.

type of equipment - crimped lugged connection attaching 12 AWG wire to fused disconnects in a 125vdc control circuit

cruciality to operation - open circuit WILL cause trip of a nuclear plant. At least a million dollars loss.

process that the equipment operates under - I'm not sure what you're asking.

I did locate some good standards in NETA MTS-1 for differential temperates. Two sets of limits - one based on rise above cabinet ambient and one based on rise compared to comparable point on similarly-loaded sister unit.

It is good to know there is no crystal ball, no timeframe. Still in order to make intelligent decisions we have to make some best guess at probability of failurem don't we? (otherwise what value is our service?). Any resources to assist in this effort would be appreciated. In particular I am interested to know any actual crimped connection failures where temperature history prior to failure is known.
 
Re:evaluate hot crimp on control wire Frgmn51 9/29/2004
Hi There may be or may not be a problem with the fuses you need to look at othe factors.
compare the ciruits to others, check current on each find ones that are close or equal to the one in question,take a voltage drop reading across the fuse include the connection is question, take voltage drop readings on other fuses of the same current draw. If there is a lower temperature reading on the others with same current and voltage drop look at the one in question a little closer.
 
Re:evaluate hot crimp on control wire scotsy 10/6/2004
I have a similiar circuit that looks alot like yours, mine also looks abnormal but after measuring the current and load I realized that it was normal.
 
Re:evaluate hot crimp on control wire electricpete 10/7/2004
Current in the lead to the left of box 3 is 1.5 amps. This is total current entering the daisy chain - it splits with portion through the fuse and portion to the other fuses.

I don't recall fuse size. It is 12awg wire which has ampacity at least 15A.
 


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