In article ,
"Dave" writes:
I'm still working my way through the latest IEE regs (it's many years since
I last had to do it) but I haven't yet seen anything about loading design.
If the CU has a 100A isolator must I ensure that the sum of the MCB trip
levels is less than 100A or can I use a statistical method (root of some of
squares) to combine the max loads on the basis that they won't all be
maximum at the same time?

They can add up to more than 100A, and there's a formula.
This is covered in the On-Site Guide, Appendix 1, Table 1B.
Note the figures are a guideline only based on typical usage. If you
have some situation where you know the figures are unsuitable, you
must adjust for that situation.

--
Andrew Gabriel