I have out of interest put my clamp meter around the tails on my consumer unit and it shows around 23 mA, as to if a single RCD rated at 30 mA would hold not sure, as I have 14 RCBO's which are MCB's and RCD's combined. We were suppose to ensure back ground leakage is less than 9 mA, however there was no place to record the leakage, so likely never measured.
The problem is we test with an insulation tester which uses 500 volt DC, but we are using 230 volt AC and the latter can leak due to inductive and capacitive leaking, so there is always some back ground leakage, and the more cable used in the home, the more this back ground leakage is.
So very likely just 5 mA can take the back ground leakage over the point where it trips the RCD, just a little damp in an outside lamp for example, and neutral to earth leakage can happen even when items are switched off.
It is also hard with six circuits to work out which has caused the problem. The regulations say "Every installation shall be divided into circuits, as necessary, to: (iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation" you have one single circuit as far as the RCD goes, so since 2008 when that regulation was published having one RCD for all has not really been allowed, however in the past RCBO's were simply not available, so electricians had little option but group many sub circuits together. It also says "(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit" we would not normally group sockets and lights in the same room on one RCD, although the way it was worded did not stop one using one RCD, and in a caravan one RCD for all is still common.
So you have to do a risk assessment, can you afford to loose your supply, before moving I lost two freezers full of food, which since I was not in the house when the RCD trips I could not claim for, which is why this house is all RCBO. But a new consumer unit is not cheap, so you need to consider is it worth it. This house my freezers are now on an UPS supply, so even if the grid fails my freezers still work, powered with the solar panels and a large battery. You need to work out how important it is to you.
