Hello, I am dealing with an office refurb and existing installation consisting of about 8 rotary isolators on a ring circuit wired with 2.5mm2 singles and fed by BS88 32Amp fuse. From as builts it appears isolators supposed to serve power poles which appears were never installed, but I would like to reuse the existing circuit to feed new HRU - about 3Amp 1ph supply. Do I need to change the circuit to radial/replace isolators with fused spurs or can I reuse one of the existing isolator? I feel I can't use the isolators but doubt arose in me when my boss said that he thinks using isolators is compliant with BS. Please let me know, thank you :)
Is the proposed 3A load internally fused or otherwise incapable of overload ? If so, then you can connect it directly - the 32A fuse at the origin protects the existing wiring and isolator, and the protection local to the load protects it. If not, then a fused spur to protect the new work where the wiring steps down from the 2.5mm to the smaller cable is probably the easiest answer - or if nothing else is ever going to be added to the circuit, then change the 32A fuse for a smaller one. (after all, if each isolator fed a couple of sockets, or a locally fused block of more sockets then you'd think nothing of a 13A fused spur fed from a ring final, and this is the same, but without the sockets.)
Certainly no need to create a new radial or remove anything unless there are other reasons that mean you want to do that anyway. Is the wiring route obvious, because if concealed and not in earthed containment, it could need a 30mA RCD or RCBO at the origin.
Is the proposed 3A load internally fused or otherwise incapable of overload ? If so, then you can connect it directly - the 32A fuse at the origin protects the existing wiring and isolator, and the protection local to the load protects it. If not, then a fused spur to protect the new work where the wiring steps down from the 2.5mm to the smaller cable is probably the easiest answer - or if nothing else is ever going to be added to the circuit, then change the 32A fuse for a smaller one. (after all, if each isolator fed a couple of sockets, or a locally fused block of more sockets then you'd think nothing of a 13A fused spur fed from a ring final, and this is the same, but without the sockets.)
Certainly no need to create a new radial or remove anything unless there are other reasons that mean you want to do that anyway. Is the wiring route obvious, because if concealed and not in earthed containment, it could need a 30mA RCD or RCBO at the origin.
