I want to add a split load consumer unit to take some of the circuits away from the existing unit and to add new ones. There is no room where the existing one is so I plan to take new tails through the wall and install the new unit in the garage.
Are there any points to be noted? For instance how high should it be mounted and how long can the tails be?
Don't like to sound unhelpful, but the fact you are asking the question could mean that a qualified electrician should be doing this work.
Have a look on the projects page on this site under part p of building regs.
Sorry not to helpful http://www.diydoctor.org.uk/projects/partp.htm KB
There are consumer units designed for Split Load and Dual Tariff with two banks top and bottom height 450mm width 241mm for 8 MCB ways from Wylex I am sure there are also other makes which may fit in the space available. The connection between the original place and new place has to follow some strict rules concerning the protection given which could require trunking, steel wired armoured cables or other items required to make this safe. Who ever designs the system will need to have the reverent qualifications and will be able to plan this. Also the Installer will need qualifications and he will verify the design. And should that all fail then the person doing the Inspection and testing is likely to pick up on it. Non of the work can be really completed by a DIY person especially when it will all be checked at some point by a professional would is likely to fail it on any parts which donâ€™t conform. To attempt to renew a consumer unit new for old is full of problems with earth leakage faults becoming apparent to which before the change the owner would not have suspected any faults. To move position as well is really asking for problems. Remember you will need as minimum tools a insulation tester which will test at 500 volts, I continuity tester using at least 200ma, I earth loop impedance tester, a prospective short circuit current tester and an RCD tester able to measure the milliseconds it takes for the trip to activate. The whole lot will also need a traceable record as to calibration and you should be able to buy the whole lot for just under Â£750 add to that the LABC fees and I suspect it will be cheaper to employ someone to do the job for you. As to qualifications you will most likely get away with a C & G 2381 which will cost about Â£275 for course and exam but the LABC may require a C & G 2391 which without some formal training would be hard to pass. You have been given the link to Part P look at pages 23 onwards and see if you think you could complete the installation cert. Remember ionisation should it happen is enough to blow a hole in a wall. It is very dangerous and fitting a consumer unit if you make a mistake you have at least 100 amp may be 500 amp to blow sub station fuse it is not like wiring a plug top wrong. And you will need the supply authority to remove and replace the supply or at least replace seals which means you can hardly do the job on the QT. I would also look at the new regulations 17th Edition.
However I am afraid you have read far too much into the question. There is no question of doing this "on the QT" and I am well aware of the implications regarding testing and have checked the rest of the web site for relevant info.
As a "Competent Person" I prefer to fully understand what I am planning and designing before deciding which elements I can do myself and what I need assistance with.
As a â€œCompetent person. A person who possesses sufficient technical knowledge, relevant practical skills and experience for the nature of the electrical work undertaken and is able at all times to prevent danger and, where appropriate, injury to him/herself and others.â€