I have a cable that shows overheating, it is on the 125 VDC UPS system, on the negative wire. The wire is 4/0 welding cable and pulling 28 amps. It appears to be getting warmer where the cable goes into a conduit run that is 10 feet in length, it cools down before it exits the conduit run. It is still below it's temperature rating but stands out as the other cables are pulling the same amount of current and not showing any kind of heating effects.
Has anyone had something similar? I would have thought the highest temp be at the connection, I never seen it at the middle of the cable before.

Any chance you can post an image? Nothing can be seen in your posting. Thanks.

It looks as though you've focused on the wire where it exits the enclosure, and as such it is not in focus at the terminal connection. Still, it appears that the source of heating is not at the connection. Where does the wire go at the other end. I would be suspicious of the environment that the wire travels through once it leaves this enclosure, or where it terminates at the other end. You will need to trace the wire back to the next location you can image to try to find the source of heating. Heating of wires from resistance heating is very rare between terminations, and typically requires that the cable had been severly kinked to break multiple strands. Another possibility is that the conduit travels through a hot area, or close to a hot pipe, and that the heating is non-electrical in nature. Good luck, and let us know what you find.

Rich Wurzbach
ASNT PdM Level III IR
Maintenance Reliability Group

The wire runs through a short conduit that runs to a disconnect, there is no heating at the disconnect side, it appears to cool down after about a foot through the wire entering the conduit. It's and ungrounded DC system so I am thinking wire defect but not certain, just wanted to see feedback on what others may have experienced in the past. I have notice hot spots on the connection point but not in the middle of the cabe, where it should hold 10 times as much current as it is pulling.

Like Rich I cant see the image posted.

Is this a single core cable or multicore?
How many other cables or cores in the conduit?
What is the temperature of the conduit and how did you measure it?
Is the conduit grounded?

Check for AC in cable/harmonic content. Expect to see high 3rd harmonic if it is causing this type of heating. Yes, AC and harmonics can occur if there are problems in the system (ie: damaged/failed or failing SCR) - or noisey ground system.

Check insulation to ground value of the cable. High leakage currents, especially in DC systems, can cause heating of cabling. Make sure that the cable is isolated from electronic components prior to testing. Test with the cable both hot then cold. Adjusted to 40C, the insulation to ground value should not fall beneath a minimum safe value of 5 MegOhms. In reality, for this short a run, the insulation value should be in the 100's of MegOhms, or into the GigOhm range.

If it is this case, the heating is the result of capacitive leakage between the cable and conduit.

Sincerely,
Howard