On 24/10/2013 21:15, Stephen wrote:

Split load does not have to mean a 50/50 split. Some 17th edition CUs
may have say 4 RCDs and some unprotected (aka "high integrity") ways as
well (for feeding circuits that meet the requirements for not being RCD
protected). You can also arrange the split in various combinations of
ways as suits your application.

One thing to bear in mind. a single RCD will take at least the same
width as two or possibly 3 MCBs. WIth 4 RCD's you're loosing space for
for your MCB's.

The beauty of a RCBO is that in the same width as a single MCB, you are
combining RCD and MCB functionality in one.

So with a 19 module wide CU, two is taken up with 2 pole isolator,
leaving you with 17 spare ways.

you can then either fit:

(a) 4 RCDs (assume double width so thats 8 ways taken) and then up to 9
MCBs for up to 9 circuits, and still have the issue of 2 or more
circuits losing power when 1 RCD trips.

or

(b) fit up to 17 RCBO's, have up to 17 circuits and if any one RCBO
trips, only one circuit is affected, leaving the rest alone.

I know which I'd prefer..... :-)

Yes I am competent to do it, just nervous that I may have missed a
fundamental flaw in the idea.

The things in my limited experience is that:

You need to ensure that your choice of CU *can* accommodate RCBOs

It often helps if you use the same make for both teh CU and the RCBOs.

It certainly does in this case, as Starbreakers use their own, specific,
plug in MCBs and RCBOs and a proprietry busbar. There's no facility for
connecting normal breakers.

SteveW