I've decided I really ought to 'regularise' the wiring of my two consumer units. A while ago one of the RCDs failed and I fixed the immediate problem by adding a new RCD 'before everything', although it hasn't caused any problems I'd like to tidy things up. There's also a discrimination issue I want to sort out.
We are rural and have a TT earthed system. The company feed comes into one of our garages where there is a standard 100 amp company fuse and now a nice new electronic meter.
The present layout from the meter tails onwards is:-
100A/100mA time delayed RCDSplit load consumer unit Non-RCD MCBs feeding garage lighting RCD MCBS feeding garage sockets and other outdoor bits and pieces. A 63 amp MCB on the non-RCD side feeds the house CU
Underground armoured cable to the house (30 metres or so)
Standard split load CU in the house with, in addition, a number of separate RCBOs.
The initial 100A/100mA time delayed RCD is the one I added because the incomer 100A/100mA RCD in the garage consumer unit failed.
I'd really like to take the house off the 63A MCB in the garage consumer unit and feed it direct. Does the following approach seem reasonable:-
'Henley' block close to meter.
One feed to a 60Amp switch/fuse unit I have already (from our original installation) which will feed the house via the underground cable.
The other feed from the Henley block to the garage consumer unit.
Replace the failed incomer on the garage consumer unit with a new 100A/100mA time delayed RCD.
Replace the present ordinary switch incomer on the house CU with a 100A/100mA time delayed RCD.
I know I *could* insert a master switch before the Henley block but it would be tight for space and, to my mind, it could be a bit confusing with the separate switch/fuse for the house only.
The house and garage/outside CUs will be entirely independent, faults on one won't affect the other and the discrimination issue due to the house CU being fed by an MCB is eliminated. There's a possible issue of discrimination between the 100A company fuse and the 60A fuse in the switch/fuse but it would take a spade through the underground cable to blow them and if that happens discrimination is hardly likely to be the major worry!
The only remaining question is that of earth rods, currently I have three earth rods, one by the house, one by the garage and one where the original incomer used to be. I have these commoned together at the moment. My feeling is to keep things that way but are there any issues that might suggest it would be a good idea to separate the house and garage earthing?
Thanks in advance for any ideas and advice.