His the sparks defence letter
As a matter of course, when looking to wire up a new item of equipment, into an existing electrical installation, we would endeavour to isolate the circuit we intend using by tracking it back to the main fuseboard and removing that specific fuse.
We found the same confusing situation on the fuseboard as their electrician has confirmed and only by the process of elimination, did we find the circuit we needed, which was the one containing the old existing extract fan.
As a matter of course, we then carried out a safety check on this circuit by carrying out an earth loop impedence test, which gave a ZS reading well within the recommended parameters.
By introducing the new fans, we have only increased the load by less than 1 amp, which should not have caused any issues.
We cannot be held responsible for the condition of the existing circuitry and can only carry out tests to the circuit we wish to attach to, to ensure it to be sound, before we continue. Had we found the fault that their electrician claims to have found, we would not have carried on and would have had to find another circuit to attach to.
In terms of RCD protection, this is not a domestic property but considered a commercial one and any electrical work should therefore be carried out by a competent and qualified electrician, if but for nothing else, for insurance purposes. Isolators have been fitted and the installation has been carried out in accordance with the latest IIE 17th Edition Regulations. A minor works certificate will be issued in due course.