Calculating volt drop

[TJC1]

When doing volt drop calcs, should you use the rating of the mcb/rcbo for the design current or the realistic current the circuit is going to use?

Just doing a calc for 40m or 4.0mm 3core swa feeding 6 sockets. Im going to wire them in a radial via b32 rcbo

 

[telectrix]

use the design current. not the OCPD rating.

 

[buzzlightyear]

Calculating Volt-Drop with the 18th Edition - https://the-regs.co.uk/blog/?p=481 there you go .

 

[Andy78]

Use design current based on a realistic usage of the sockets. If it will be as high as 32A then my rough calcs see you at 6mm for a single phase circuit.

 

[Deleted account]

I agree design current, but I usually do the max possible loading also just to check.

I then inform customer of results saying “this cable size is fine for the load information you have supplied, but if you use the max load the breaker can supply the volt drop would be....”

Either fine or not.

The customer then sometimes come clean with what the actual loading could be if the volt drop is not acceptable at the higher load. Quite often customer will request larger cable size.

Not Necessary, but good practice.