How to calculate the temp. a cable will reach?

On a graph you can calculate that you can use a 35mm 4 core armoured cable for 100Amps over 120m, but the cable is rated maximum 70C. How do you calculate what temp a cable will reach at a certain load?
asked 5/15/2012

4 Answers

There is software for doing this such as:

CableCALC HV -


answered 12/17/2012 battler. 2
I do hope to do a IEC 60287 cable sizing post someday. It is on my list and I will get round to it, but it is not top priority, so it may take a little time.
answered 5/30/2012 Steven McFadyen 246
Steven McFadyen
Please publish the formula in IEC 60287 & sample graph or table for a given type/size of cable. After derating the cable for ambient conditions we can calculate the temperature.
answered 5/30/2012 naban 6
Thanks for the great question. Unfortunately I don’t think the answer is that easy. Two ways that come to my mind:

1. Analyzing cables is a thermal balance problem. Heat is added to the cable (copper losses, sheath losses, solar radiation, from other cables, etc.) and removed via conduction (through the cable and surrounding environment). By balancing the heat entering the cable with what is leaving you can work out the temperature. Al l the necessary formulae for this are given in IEC 60287, although it is quite complex and does not lend itself to manual calculation – you will likely need software.

2. Simpler (but less accurate) would be to assume that temperature is proportional to the copper losses (current squared times resistance). At zero amps, the cable would be a ambient; at maximum current (from your graphs or tables) it would be at 70oC. You could use the square of the current to interpolate between these extremes to get the temperature for the actual load current. As the resistance of the conductor decreases as the temperature increases, you could consider also add this factor into your calculation as a further refinement.
answered 5/16/2012 Steven McFadyen 246
Steven McFadyen

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