Consumer unit question RCD vs RCBO

size, cost & discrimination.

NT

Snip

I just noticed the other thread that I missed before, so basically opting for the main switch +3*RCBOs is perfectly fine?

Lee

RCBOs are preferable as a 'leakage' fault only takes out that circuit. With a whole CU RCD, the same fault takes out all. Also helps with fault finding - as you'll know which circuit the leakage is in.

It's better than MCBs as Dave explained.

NT

All RCBO solutions are usually "best" in most circumstances. The only exception being if you specifically wanted a circuit without RCD protection - but in that case you could simply drop an RCBO for a MCB.

In a normal domestic installation, what would a circuit have to supply to make that a sensible option?

Some things can 'leak' slightly. Enough to trip an RCD while working normally. Things like immersion heaters - that type of heating element. And multiple SMPS - a room full of computers.

Now you could argue a heating element shouldn't 'leak' - but it's unlikely to cost more to run if it is switched off when not in use. Nor does something permanently wired usually present a safety hazard.

Fire alarm system (separate to lights), medical equipment and refrigeration are all options.

Typically things like:

Sub-mains - feeding other CUs (so you can maintain discrimination between circuits in the slave CU)

Circuits where you want a very low trip risk (Boiler, frost protection, or freezer supply etc)

High reliability circuits - fire protection, medical equipment, some lifting gear etc.

Circuits that tend to have high leakage currents combined with very low shock risks like mineral insulated heating elements in damp environments (immersion heaters, cookers etc)

PV

Not supplying a non RCD way is a good way to upset them when they do their install:-)