I have a standard 4/5 way rcd protected fuse box proteus type fitted 2 years ago,fully tested and certified, fuse 4 is the cooker radial only in use for my garage/workshop fed direct from MCB on 6mm armoured cable i have a Memera 2000 with a range of fuses 6A lighting 5 16A for indivdual sockets 1 20A for a circular saw that can peak at 16/18 amps on start up, 13/15 amps running, every thing works fine. do i need a rcd unit on the garage MCB ? or is the one in the house sufficient? the run to the garage is approx 10m any help would be appreciated.
Are you a tradesperson and able to answer this question?
Since the cable is running from the house, and based on your description all circuits are protected by RCD, you don't need separate RCD protection. Having said that it will be annoying if you're working in the workshop and it trips the RCD and will end up tripping all circuits in the house. It's probably worth converting the MCB that's for the workshop to a RCBO so it will trip independently to everything else. But this is based on your description which isn't absolutely clear.
If possible I would put the circuit on a mcb independent of the main rcd and then put an rcd in the garage so in the event of a trip you don't have to venture back into the house. You do not need two though.
The sub main cable from the house consumer unit does not need RCD protection.
(you state it’s armoured)
If your house consumer unit is split with 2 x RCDs then likely to already be rcd protected then it is what it is.
The best solution is to feed the sub main cable from a non rcd way in DB preferably a C type mcb and have a high integrity consumer unit in the garage all on separate B type rcbos to prevent inconvenience in the event of a fault and aid fault discrimination.
