Volt drop from Cable length Calculator

Note:- It is considered with RCD protection there is no requirement for exact Zs information as long as it will trip the RCD that is good enough. However the prospective short circuit current ideally should still be high enough to trip the magnetic part of the trip so this is calculated here.

Measured Ze Ω i.e. at consumer unit. Measured PSCC i.e. at consumer unit. Cable length meters. Size of Line conductor Size of Earth conductor Ring Main
Ω   Amps. Meters.
Ambient temperature Nomial volts Max permitted operating temp tp Rating factor for grouping Cg Rating factor for ambient temperature Ca Design current for circuit Ib
°C Volts. °C Amps.

Tabulated current-carrying capacity of a cable It Orignal mV/A/m Corrected mV/A/m Volt drop for power should be less than 11.5 volt (5%) lights 6.9 volt (3%). Correction factor Ct Expected PSCC i.e. at circuit end. For a B32 MCB should be over 160 amp. Zs i.e. at furthest point or mid position. Total Impedance of Live conductors
amps. Volts. Amps. Ω  

Click on Calculate to get results. The default settings are for a ring main at maximum length with a 32A B type MCB/RCBO with a TN-C-S supply with a ELI of 0.35Ω the idea being to identify when parameters have been exceeded when doing an EICR. In this version no account has been made of the earth, it is assumed protected by RCD so is not a problem with normal installation. With the Design current for circuit (Ib) once the calculate button is hit a suggestion is made. It is assumed with ring the 20 amp plus half remainder is used but with radial it is the total of the MCB fitted. The suggest figure is what one would expect, but with a single appliance this may be much lower.

This has been made following theory, but as yet unconfirmed as to it these figures bare out in practice. The mV/A/m of the earth cable is not corrected.