Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Replies 7 replies
  • Subscribers 34 subscribers
  • Views 1507 views
  • Users 0 members are here
Options
You may also be interested in

Multicore cable calculations

Martin Coward

I am instaling a piece of equipment that has a total loading of 4.5kW, but am constraint on space to run cable from the starter to the equipment. I intend to use a 7 core cable, of which only three cores are for the 3phase power the remainder are for start / stop and indicator light. Power is supplied via an MCCB and 2.5mm cable is large enough to run the cable even with the derating factor of multicore cable. My problem is the impedance, (Zc) value is adjusted by the 7 cores meaning a 4mm cable is needed as opposed to 2.5. Is it acceptable to calculate using 3 cores as these are the only cables carrying power or is 4mm cable required.

Parents
  • 0

    In the ROI we effectively use Mike’s method. There are no voltage drop tables. If you want to know the voltage drop you have to use a given formula base on resistivity of copper at 70C and a set reactance value across all cross sectional areas then multiply by 2 for single phase or root 3 for three phase.

    However, using Mikes method won’t take you a million miles from a more fastidious approach.

    If you have a 4mm2 copper cable, for example, one core will have a resistance of around 20 divided by 4 milliohms per metre. Similarly a 10mm2 core will have 20 divided by 10 milliohms. 
    Those can be multiplied by 2 or root 3 to five the single phase or three phase values per metre length of the circuit.

    have a look at Table B1 in GN3 or the voltage drop values in say Table 4D2B in Appendix 4 of BS 7671 and you will see the results are not too far apart!

Reply
  • 0

    In the ROI we effectively use Mike’s method. There are no voltage drop tables. If you want to know the voltage drop you have to use a given formula base on resistivity of copper at 70C and a set reactance value across all cross sectional areas then multiply by 2 for single phase or root 3 for three phase.

    However, using Mikes method won’t take you a million miles from a more fastidious approach.

    If you have a 4mm2 copper cable, for example, one core will have a resistance of around 20 divided by 4 milliohms per metre. Similarly a 10mm2 core will have 20 divided by 10 milliohms. 
    Those can be multiplied by 2 or root 3 to five the single phase or three phase values per metre length of the circuit.

    have a look at Table B1 in GN3 or the voltage drop values in say Table 4D2B in Appendix 4 of BS 7671 and you will see the results are not too far apart!

Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines