Discuss Length of cable in the Electrical Engineering Chat area at ElectriciansForums.net
Does the length of cable de rate the cable as it creates a greater resistance and as a result heats up the cable reducing its current carrying capacities?
Yes, at a point you would find it fails to meet the VD or disconnection limits.My question was if the circuit say was run in 1.5 cable and can take 10 amps if I had a long run would that reduce that 10amps sorry for being unclear. Thanks for your help guys
Agreed pc1966, the wording of the question does'nt help and of course many other things to take into consideration but got the impression trainee asking a simple question looking for a simple answer! We all know though nothing is that simple or straightforward when it comes to circuit design.I think we are all looking at the OP's statement from differing points of view!
Yes, at a point you would find it fails to meet the VD or disconnection limits.
So as the length increases from near-zero you have a constant limit, the thermal CCC, but then you reach one or more points when you need to derate it to maintain either the required VD (say 5% or 3% for lights), or to allow adequate fault clearance.
Maybe, you would need to limit the circuit current but you really need to do some proper circuit calcs to be sure. It wont drop automatically to 5A as in your example.So say for an example it could take 10 amps at 10 meters if we went up to 100meters would we expect that to drop to day 5 amps for example?
It depends on the application:So say for an example it could take 10 amps at 10 meters if we went up to 100meters would we expect that to drop to day 5 amps for example?
It depends on the application:
They will give you different current limits for the same cable!
- Is it 3% or 5% drop you have to meet?
- Are you on 230V single phase or 400V three-phase?
the main question I was trying to clear up was that when the length of the conductor increases so does the resistance meaning the conductor gets hotter and effecting the current carrying capabilities.
Heat per unit length is exactly the same. Total wasted power is higher, of course!Surely an excessive volt drop from a very long run would cause the conductors to heat up.
Yes but is the cable run vertically? Then the hotter air will rise and heat your cable more.No. Think about it - if you keep the current the same but double the length, then you double the resistance and double the heat generated. But, you have also doubled the length of the cable - so the amount of heat generated per length of cable is exactly the same.
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