Yes afraid so, any addition or new circuit needs a Type A Rcd unless you can prove that anything used on that circuit does not have any internal electronic circuitry.....A real ballache having to explain that to a client who had a new CU fitted last march with AC rcd's and now wants two extra sockets in lounge and has to have rcd replaced
I think we need to be more pragmetic about this than ripping out almost brand new type AC rcds just because an extra socket is required. Yes, there is new a requirement that RCDs are a minimum of type A unless load is strictly resistive, so of course any new ones we fit should be type A. However where the type AC RCD is existing and you are just adding an extra socket its more of a grey area, the issue with compliance is with the existing arrangements, and while yes, there is a a requirement to make sure that what is existing can be extended without compromising the safety of the new work, you have to ask yourself if that is an issue in this situation when maybe they are not adding any extra loads, they just want extra sockets to get rid of the extension leads running all over the place.
Its worth remembering, that while DC-loking of RCDs is plausable (theres a patent out there that covers a circiit that does that, which was incorpated into a particular brand of loop testers - and its dated over 30 years ago, this isn't a newly discovered effect) and it can be replicated on a bench, the chance of a fault occuring which causes this is probably not too likely, it can certainly happen, but I would expect a low impedance N-E fault close to the RCD, as well as RCDs which themselves just die and fail to operate to me much more common causes from RCDS which failed to trip than a type AC where it should have been a type A.
Maybe we should do a quick mental risk assessment of what loads are being added vs. what is the outcome of the RCD being in/op (obviously loosing additional protection for an outdoor socket, is worse than loosing additional protection to a surface clipped domestic lighting circuit). Of course we should also extend that to cirucits which don't actually require RCD protection, but end up on one anyway because its a dual split board, the airconditioner cirucit in SWA for instance, doesn't need RCD protection, so I'm sure a theres quite a few who woulnd't even worry about the type AC RCD ("Doesn't need RCD anyway mate, so that type AC is fine 'cos its it don't actually need nuth'ing) when that RCD also protects the downstairs sockets and the aircon will have a larger VSD than anything else you could forseeably install in a domestic installation.
The way things are going, the average consumer unit will have a lifespan of less than the average kitchen, I expect we will be ripping out a load of boards again when the 19th edition gets here as many of the makes won't have AFDDs available for the older ranges and they'll be required on a lot of the circuits.
