heat on cable terminal MCC

[jpamungkas]

hi, we have a thermograpy test,showing excessive heat in cable power near breaker MCC for motor 15 kW. Our cable rating is capable to bring the motor load. Temp is about 50degC. this phenomenon only occur on sharp bending of the cable. anyone can tell what actually happen?
thanks before.

 

[itsmoked]

A common problem is induction heating caused by metal structures separating the phases. Is there anything separating the phases at your turns?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[asekhar]

Could be the lug is not fitted properly or the termination surface is uneven causing insufficient contact.

Anand Sekhar

 

[itsmoked]

Welcome asekhar.

He sez it only happens at a bend in the cable not really at a cable lug connection.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jpamungkas]

thanks for the quick replies to you all.yes right! this problem only occur in the bending,not because poor connection. it separated with nothing, only cable it self. is it any possibility of cracking inside the cable?

 

[dV8r]

Not likely cracking but not impossable either. Most likely due to a slight decrease in the diameter of each strand within the cable as it is bent into a too short radius. This is one reason that cabling has recommended minimum bend radius information. This along with maximizing the cables current carring load could cause a problem. But is 50 Deg C a problem? Maybe, maybe not?

 

[jpamungkas]

some location even showing hotter than 74 degC. about the carrying capacity, this cable more than suitable enough to carry the current. installation need a sharp bending because of little space in cubicle.

 

[Tmoose]

Is this at 50/60 Hz, or a higher frequency?

 

[jpamungkas]

it is 50 Hz.

 

[HCBFlash]

Actually somewhat typical for tight bends, I expect to see it. Some of what you'd be showing is thinning of insulation on the back of the bend, which always affects photo-infrared viewers showing as hot spots. It is also typical for some strands to be damaged by extremely tight bends because of the methods used to obtain them.

Is your cable in fact correctly sized (to obtain a lower operating temperature)? I'm doubtful. What factors were used in determining it's size? Remember that cable sizing is based to some degree on conductor temperature, which is why higher temperature rated insulation on cables show higher ampacity on sizing tables.

Running load amperes should be measured and compared to ampacity charts for the size (circular mils or gage). This is a simple way to determine the expected operating temperature for the wiring. Especially if you have moderate to extended startup time, the additional heating from that additional startup current will not just disappear when the current drops. Time between startups and unloaded time are all factors.

You also mention small space in the "cubicle". This is also another factor which contributes to higher temperatures. Is the MCC placed for good ventilation and cooling? Do the cables run high in the MCC? Heat from all other cabling, thermal units in other starters, transformers, VS drives,etc will contribute and rise to the top of the MCC.

LOTS of considerations. 50' C isn't very hot at all in my experience. Perhaps it ought to be, but it's not likely with all efforts being put into minimizing costs particularly as opposed to heating.



flash

Me wrong? I'm just fine-tuning my sarcasm!