i am replacing an old earth trip on a tt insulation.
i should had got a 100ma rcd, but by mistake i have a 30ma.
if i fit the 30ma rcd and it causes no problems is it ok to leave it or MUST it be a 100ma.
If there really are no problems then there is no regulation that says you cannot have a 30mA RCD as your main switch, but... All your lights will go out if you plug in a faulty appliance that causes the rcd to trip, or if you get a socket wet.. or any other accessory for that matter. 30mA RCD's are for supplementary protection from electric shock, but are prone to nuisance tripping, which is why most modern installations have a split load consumer unit. It's up to you, but I'd get a 100mA RCD for your main switch.