Compressor cables getting warm.

[dlt27]

Hi all,
A maintenance friend today asked for a bit of advice. He said cabbles supplying compressor are very warm / hot to touch. (Also thought he could feel them vibrating slightly)
The cable is a swa 25mm and is pulling 55A per phase. I said being a compressor it might have a VFD and might be causing harmonics.
All I wanted to know is because I don't really understand harmonics etc am I wide of the mark and if so what could be causing cables to get hot and who should he call in to look at it.
Thanks again for any info...

 

[Deleted member 26818]

Solution will be to use larger CSA cables.

 

[Andy-1960]

How hot is hot? Have you measured the temperature?

 

[Bobster]

One VFD will not generate harmonics enough to cause that issue. No at the size it is. An most likely it's not using a neutral anyway.

Remember, cables are rated to operate at 70degC. Has he actually measured the temp, because just touching the cable with a hand isn't good enough.

Also, the hot weather you guys are having currently is bound to play a part into it.

 

[marconi]

What are the measured currents in each line?

http://www.aeicables.co.uk/literature/CurrentRatings.pdf

The volt drop per m for 25mm 3/4 core clipped direct 30C ambient, 90C conductor temperature is 1.65 x 10exp-3 V/A/m
So, Joule heating per m per conductor is volt drop/m x current x current =

1.65 x 10exp-3 x 55 x 55 = 5W/m

or 15W/m for 3 core cable.

 

[marconi]

I am not surprised the cable is warm. Each conductor is surrounded by three layers of plastic insulation and at the moment the ambient air temperature is high 20s maybe more inside the factory. So, conductor temperature will be higher than during periods of cooler ambient air in order produce a temperature gradient between them and surrounding air sufficient to cause a heat flux of 15W/m. Check the temperature rating of the SWA cable.

 

[Wilko]

Hi - The 25mm cable is running approx half its rating assuming no harmonic content. If somehow there were harmonics, the highest example of harmonic content given in BBB would see this still being within 25mm capacity, I reckon (42% THD on p380). Perhaps have a look for signs of heat damage near terminations? And then have a cool drink, or at least I will .

 

[dmxtothemax]

Very warm & hot to touch
are both very relative terms
Get an accurate temp measurement
remember these cables can run up to 70
so 30 or 40 would not be cause for concern.