17th Edition CU (garage consumer unit)

Hi. The cable that supplies the garage unit with power may very well need RCD protection itself. This RCD (or RCBO) will need to be located at the cables origin (i.e. in the main consumer unit of the house). It could be considered bad practice to fit two 30m/a RCD's in series like that because, in the event of an earth fault, either or both of them could trip (this would be considered impractical and inconvenient). A circuit only requires to be covered by one 30m/a RCD which is already in the main consumer unit (if it isn't, then that needs doing first), so only a main switch is needed in the garage unit. So all you need to do is change the RCD supplied with a standard main switch. Hope that helps.

The unit you describe is not compliant with BS7671:17th edition. You also need to be very wary of cheap Chinese made boards on ebay. Best bet is to get a decent brand such as Wylex, Crabtree, MK or Hager from somewhere like screwfix.

I agree with electrical safety services. I assume that this new consumer unit although being fitted in the garage is to serve the house?? I would fit a Wylex or MK board personally - these are worth the extra pennies and you know that if certain breakers were to become faulty in future you an get replacement parts. Go to an electrical wholesaler in your area - if eBay seems cheap then you are buying cheap. I haven't met an electrician who has ever bought a board from eBay.

Simple answer = Hire an electrician...and leave them to supply the parts.

yes this unit does comply with the regs as long as the cable feeding the unit is also rcd protected at the origin of the supply although you may have to look at your earthing arrangements to ensure the DNO are ok with where you are fitting it.

Yes your fine

The consumer unit if fine. The RCD would be the main isolator as it isolates everything in the CU

I think more information is required before an opinion could be offered. What is the size of the cable supplying your garage and from where does it derive its supply? Is it supplied from your existing consumer unit within your home and if so what size in amps is the mcb to which it is connected. Or is it supplied separately from the meter? Did the other electrician visit your home to make his/her assessment? A competent electrician can take in a lot within minutes of being on site. My advice would be to get someone on site to discuss each aspect of your needs.