Thanks for the replies, but what I am asking is about the protection feeding the garage consumer unit? The garage consumer unit has a 30ma rcd and 2 mcb's for lights and sockets. What I don't want is a 30ma rcd feeding another 30ma rcd from the house to the garage. As this is a domestic premises reg 411.3.3 requires additional protection for sockets not exceeding 32A via a 30ma rcd. And reg 411.3.4 requires that AC final ciruits with luminaries requires additional protection via 30ma rcd. As this is not an "AC final circuit" I'm asking what is normally best practice. As it will be a clean run of SWA cable between the 2 is it best to use a switch fuse from the house to the garage or a 100ma rcd and mcb. My thoughts are that an rcd would be the better option. Yes the garage can be a TT system.