Can anyone help to clarify what the maximum cable length for a ring final circuit is (conditions below).
The maximum surface area that a ring circuit may provide for is well documented being 100m^2, this of course can have various cable lengths from 10m*10m=40 meters to an unlikely 100m*1m = 202 meters length. In addition it is often quoted that the maximum cable length is 50 meters is permissible in a ring final circuit wired in 2.5mm^2 with a cpc of 1.5 mm^2, however the OSG quoted figures don’t seem to agree with this…. Information from table 7.1, pg 42, OSG: For a device rating of 32A and cable size phase/cpc of 2.5/1.5 mm^2, with a Type B CB, M6 cable installation in PVC (without de-rating) and a Ze <= 0.35 ohm with the TN-C-S earth a maximum cable length of 84 meters is given. Is 84 meters the correct figure? (without considering de-rating for thermal conditions etc).
The reason why I’m asking: The final ring installation I’m planning is 17 meters from the consumer unit to the first / final socket in the ring. The supply from the CU has to go via a single story building (above bathroom & kitchen) prior to entering the main body of the house where the two ring mains are. The route of the cable shall be in the ‘single story’ loft space so I will take into account thermal de-rating as the temperature is liable to rise above 30C in summer.
Any help on this one appreciated.
Supply Information:
Supply 240V, Single Phase, PSCC = 16KA via BS1361 cartridge fuse in termination.
Earthing Type: PME terminal, Maximum earth loop impedance = 0.35R.
Installation Details:
Ring final circuit protected by Type B Single Pole MCB (MK 5932s, 32A).
The maximum surface area that a ring circuit may provide for is well documented being 100m^2, this of course can have various cable lengths from 10m*10m=40 meters to an unlikely 100m*1m = 202 meters length. In addition it is often quoted that the maximum cable length is 50 meters is permissible in a ring final circuit wired in 2.5mm^2 with a cpc of 1.5 mm^2, however the OSG quoted figures don’t seem to agree with this…. Information from table 7.1, pg 42, OSG: For a device rating of 32A and cable size phase/cpc of 2.5/1.5 mm^2, with a Type B CB, M6 cable installation in PVC (without de-rating) and a Ze <= 0.35 ohm with the TN-C-S earth a maximum cable length of 84 meters is given. Is 84 meters the correct figure? (without considering de-rating for thermal conditions etc).
The reason why I’m asking: The final ring installation I’m planning is 17 meters from the consumer unit to the first / final socket in the ring. The supply from the CU has to go via a single story building (above bathroom & kitchen) prior to entering the main body of the house where the two ring mains are. The route of the cable shall be in the ‘single story’ loft space so I will take into account thermal de-rating as the temperature is liable to rise above 30C in summer.
Any help on this one appreciated.
Supply Information:
Supply 240V, Single Phase, PSCC = 16KA via BS1361 cartridge fuse in termination.
Earthing Type: PME terminal, Maximum earth loop impedance = 0.35R.
Installation Details:
Ring final circuit protected by Type B Single Pole MCB (MK 5932s, 32A).