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Hi using 25.0mm tails and a 16.0mm earth gets over any bonding issues and the way you could run the supply to the second consumer unit is to use a small 100amp switch fuse which you could rate at 60 / 80amps which are readily available (assuming a standard domestic installation supply) to provide some discrimination over the supply fuse and any load on the existing area. The only problem is that the cabling needs to be below 50mm to comply with the current regs on buried cables otherwise this requires RCD protection and therefore an SWA would be required to comply with this unless you can meet the conditions of the regs by protection, placing in a route where it is not going to be subject to being nailed through and deep enough. Of course if this is a TT supply it will require RCD protection anyway? I am assuming a TN-C-S / PM-E supply in this instance but you also need to check the earth loop of the incoming supply and disconnection times of the BS fuse used in the switch fuse for disconnection times over the length of the cable run and final circuits fed from there on in. I am further assuming that the final circuits will be twin and earth and less than 50mm buried and will be RCD protected thus using a 30ma RCD given the touch voltage of 50v divided by the trip current allows a maximum earth loop value of 1666.66 ohms. A more realistic value on a TN-C-S /PME installations is likely to be at maximum 0.35 ohms at the origin and final circuits not in excess of the rated values for Mcb's as per Current IET wiring regs.
Probably a a bit over the top but hope this gives a good guide and this is how I would approach it.
Don't you just hate it when customers go off and have half the information and because we drive a van they instantly know more than we do with only part of the information GOOD LUCK!
Probably a a bit over the top but hope this gives a good guide and this is how I would approach it.
Don't you just hate it when customers go off and have half the information and because we drive a van they instantly know more than we do with only part of the information GOOD LUCK!