RCD Calculations

[JUD]

Back again!

Thought I would check my DB (which has been in about 5 years) and see if calcs work out. Please advise if I have worked out correctly.

Main switch 100A this feeds

• 8 MCBs 32A x 1, 16A x 2, 20A x 1, 6A x 4

• RCD 80A then covers 5 more MCBs 32A x 3, 20A x 1, 16A x 1

Working on 100% of highest rating circuit (32A) then 40% of remaining circuits (208A @ 40% = 83.2A) giving a total of 115.2A which is higher than main switch. Therefore my DB is out of existing regs?

Thanks for your patience!

But what are the design currents of the circuits themselves.

For example, a lighting circuit, although it is on a 6A breaker, may not be drawing 6A. These are the figures you need to use for your calculation.

 

[mmax6870]

Hi JUD,

The DB was in before I started thinking about becoming a Sparky so I guess the design currents would have been calculated using diversity guidelines, this in turn would determine which size MCB is required I guess.

I was hoping that there would be some calculation, based upon the existing MCB ratings, which could be applied to determine whether there was any remaining capacity on the main switch?

Cheers