Installing an RCD?

[1john]

It's kind of hard to say no to that question. IMHO i would advise upon having a PIR done before the installation of RCD's RCBO's or consumer unit upgrades, as i myself wouldnt undertake any of those jobs without prior testing.

It doesnt look good to install things that will leave the customer facing either no electricity or a suprise bill for fault finding which they were not previously warned or notified about.

 

[kai]

It can be better to replace the entire CU when buying a second hand house that's more than about ten years old, You will NOT know know the condition of the old breakers, and were they subjected to a heavy fault current etc.
Just suggesting - it can be safer than faffing around with the existing consumer unit.