- Reaction score
- 2,810
I'm with e54, why would you derate a parallel cable, it seems pointless, they are both of the same origins and circuit destination so why would you not treat them as 1 cable.?? Or am I missing something?
Discuss 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fuses in the UK Electrical Forum area at ElectriciansForums.net
The larger won't emit MORE heat, it will emit the same amount of heat energy dissipated over a smaller surface area than the two parallel conductors which have a greater surface area - this is basic radiator principle. If N amount of electrical energy passing down R resistance of copper will produce J amount of heat, J becomes a fixed form. So all we are left with is simply J/circumference, of which 2 x ccc's are roughly 1/3 larger than a single one double the size. Do the maths if you don't believe me!
OK guys, it looks like I'm the only one here that applies a grouping factor to cables that are run in parallel (that are touching, Table ), when they feed a single source. So please can someone explain why they don't. As I posted in #40
(example 1:same source supply) We have 2 cables (touching, in ducting) each drawing 100A (the source requires 200A) The cables are of the same size and are both 30 meters long. You are saying you would not de-rate these cables as they are supplying a single sourse
(example 2: 2 separate sources) We have 2 cables (touching, in ducting) each drawing 100A (each source requires 100A) The cables are of the same size and are both 30 meters long. You are saying you would de-rate these cables.
You de-rate the cables due to heat disipation. Example 1 cables are producing the same heat as example 2 cables. In layman's terms, so a thicko like me can understand, why de-rate example 2 but not example 1? What is the logic in that... They are the same..
I have done the Maths lol, if think you need to!!
Example Table 4E1A
Ib = 700 amp, 2 Phase, Cables touching Ref Method C
2 x 150mm CSA
1 x 300 mm CSA
Your argument is missing a few key point's
2 x 150 = ccc = 952 amps
1 x 300 = ccc = 743 amps
Power dissiapted = I2R
Exactly my point about using worst case correction factors!! Your actually reducing any heat, by using two smaller CSA cables that ''CAN'' carry considerably more current, but actually isn't!! Who in their right mind would install a circuit that is going to be on it's limits?? lol!!
Do you apply a grouping correction factor to a circuit run in trefoil too?? Adds up to exactly the same thing after all!!
I have done the Maths lol, if think you need to!!
Example Table 4E1A
Ib = 700 amp, 2 Phase, Cables touching Ref Method C
2 x 150mm CSA
1 x 300 mm CSA
Your argument is missing a few key point's
2 x 150 = ccc = 952 amps
1 x 300 = ccc = 743 amps
Power dissiapted = I2R
Exactly my point about using worst case correction factors!! Your actually reducing any heat, by using two smaller CSA cables that ''CAN'' carry considerably more current, but actually isn't!! Who in their right mind would install a circuit that is going to be on it's limits?? lol!!
Do you apply a grouping correction factor to a circuit run in trefoil too?? Adds up to exactly the same thing after all!!
Reply to 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fuses in the UK Electrical Forum area at ElectriciansForums.net
We get it, advertisements are annoying!
Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.