RCD protection in an IT run office

Well Zoom, we have discussed this many times before. As Andy summarises the regs now are fairly clear (18th Amd 1) but in reality, it is not very dangerous unless one gets very unusual faults on the "Fixed wiring" to the sockets. Most of these installations should get a C3 and note that changing this to BS7671 compliance now, would be somewhat expensive because many more final circuits would be required, or the installation changed around to have an RCD local to a few sockets so that the leakage from the lot summed is less than about 10mA. At the same time, one might add high integrity Earthing to the circuits back to the board the installation is then completely compliant. It is a problem for offices with much IT equipment, as summed leakage can become quite high if there are perhaps 20 computers taking less than 3kW together but together having a leakage of 100mA. There is another point, which is the spectrum of the leakage current, and whether this will trip a typical RCD. Some is 50Hz so will, but the rest is entirely unknown and may be harmonics of 50Hz and switching frequencies and all kinds of frequencies to which the RCD may not be sensitive. The easiest way (which I have not seen anywhere!) would be to have a garage size CU by every desk with an RCD/MCB/RCBO feeding a number of local sockets. The feed to all these could be a high current ring, providing the high integrity Earth and power of whatever is needed. Fairly easy to install, even for island desks with a floor trap, and very fault resistant on any plugged-in equipment. I wonder if anyone else has seen this or any other ideas?

Well Zoom, we have discussed this many times before. As Andy summarises the regs now are fairly clear (18th Amd 1) but in reality, it is not very dangerous unless one gets very unusual faults on the "Fixed wiring" to the sockets. Most of these installations should get a C3 and note that changing this to BS7671 compliance now, would be somewhat expensive because many more final circuits would be required, or the installation changed around to have an RCD local to a few sockets so that the leakage from the lot summed is less than about 10mA. At the same time, one might add high integrity Earthing to the circuits back to the board the installation is then completely compliant. It is a problem for offices with much IT equipment, as summed leakage can become quite high if there are perhaps 20 computers taking less than 3kW together but together having a leakage of 100mA. There is another point, which is the spectrum of the leakage current, and whether this will trip a typical RCD. Some is 50Hz so will, but the rest is entirely unknown and may be harmonics of 50Hz and switching frequencies and all kinds of frequencies to which the RCD may not be sensitive. The easiest way (which I have not seen anywhere!) would be to have a garage size CU by every desk with an RCD/MCB/RCBO feeding a number of local sockets. The feed to all these could be a high current ring, providing the high integrity Earth and power of whatever is needed. Fairly easy to install, even for island desks with a floor trap, and very fault resistant on any plugged-in equipment. I wonder if anyone else has seen this or any other ideas?