Maximum length allowed for final circuits

by Steve on May 6, 2009




What is the maximum length allowed for final circuits?



There are many factors which will affect the maximum allowed length of cable runs for final circuits. Calculations must be made to take into account

  • Type of supply

  • Installation (Reference) Method

  • Ambient Temperature

  • Protective Device

  • Conductor Material

  • Volt Drop


But don’t panic!

Turn to the Final Circuits Section of your On-Site Guide where you will find the calculations have been done for you.


The tables in this section give Maximum Cable Lengths for Final Circuits in Domestic Premises or similar using PVC Insulated & Sheathed Flat Cables.


Ring Circuits

A point worth noting with Ring Main circuits is that care must be taken to equally distribute the load between the legs of the circuit.


Where installing a Ring Main circuit which could supply a washing machine, tumble dryer and/or dish washer and all appliances are near to one end of the circuit, then consideration should be given to installing a separate Ring or Radial circuit.


Source information:


BS7671:2008- Appendix 15 Ring & Radial Circuit Arrangements.

On-Site Guide -Standard Circuit Arrangements Appendix for information.


Commonly used Installation/Reference Methods

Quick Reference Link to

Installation Reference Method Codes



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