How can I tell if my fuse box has an RCD?

You currently do not have a RCD in your fuse board if you are upgrading or putting new circuits in then yes you would need to RCD protection to those new circuits.

You can get RCBOs and replace the MCBs. You can either do that for all or just the individual circuit. RCBOs are MCBs and RCDs in a combined unit. The can be easily interchanged with MCBs on most Consumer Units. ——— @IR https://www.se.com/ie/en/product-range-presentation/1098-qwikline-ii/ The reason you cannot use mixed brands is because it voids manufacturers’ warranties. In this case Schneider have bought out Square D in 1991 and slowly closed them down whilst taking over their product lines. They specifically sell the same products and state they can be used with Square D units and bars, so we can safely put some Schneider qwikline II breakers in Square D units.

Square D is an obsolete brand. When I'm working I flat refuse to mix brands of circuit breakers. I think Schneider RCBO's might fit, just make sure whoever does your electrical work is registered and willing to provide a certificate for completed works. NB. An RCBO is a circuit breaker with an integral RCD.

At the time of installation of your consumer unit rcd protection wouldn't have been required. If you are not going to do any work to your electric then it most likely isn't needed to have rcd protection. However if you are too undertake some electrical work I advise you have an EICR carried out (electrical installation condition report) this when carried out correctly will tell you all the things you may need to do to improve the safety of your electrics