Volt drop and Cable length from loop impedance Calculator

Measured Ze i.e. at consumer unit.  Measured Zs i.e. at furthest point or mid position on a ring.  Size of Line conductor Size of Earth conductor Ring Main Ambient temperature
°C
Nomial volts Max permitted operating temp tp Installation Method Rating factor for grouping Cg Rating factor for ambient temperature Ca Design current for circuit Ib
°C
Tabulated current-carrying capacity of a cable It Tabulated
mV/A/m
Corrected mV/A/m Cable length meters Volt drop Impedance of Line conductors Correction factor Ct
L   E   L   E   Ω   L   E  

In 2008 the then new wiring regulations in Appendix 12 changed the permitted volt drop when supplied directly from a public low voltage distribution system from 4% to 3% for lighting and 5% other uses. It was not retrospective, but it means additions to an existing lighting circuit would need to comply. The problem was how to measure volt drop. The supply voltage varies, and it needed to be measured with consideration of the load likely to be applied. At an IET meeting the members were saying how the new rules resulted in a longer ring of 106 meters, but quick calculation did not agree with this figure. One meter most of us have is the earth loop impedance meter, and with a TN-C-S supply these reading could be used to calculate the volt drop, and with it the cable length, but there were also correction formula to be considered, and to sit down and work it all out for each circuit was a daunting task. So I decided since my phone at the time ran Excel, an Excel program was the way to go. However later phones started to charge extra for Excel, so then it was better to move to Java Script. This had a huge advantage, I could publish in the net, and others could test my program, and I will admit there were some errors. My thanks to the members of DIYnot for their assistance, and specially JohnW2 and EFLImpudence who identified some blatant mistakes? I hope now all bugs have been removed, but I did use the Excel version for 6 years without realising there were errors. However with both the 6.9 volt “lighting”, and 11.5 volt “other”, allowance one would hope is not taken to the limit. I have made three other versions going in different directions, and added installation method. Main formula is 6.1 "correction for operating temperature" page 258 original red BS7671:2008, and the Table 4D5 - 70ºC thermoplastic insulated and sheathed flat cable with protective conductor page 282 same book, is used to get the tabulated current carrying capacity and tabulated mV/A/m.