Back-up power supplies

Where un-interruptible power supply (UPS) systems feed workshop supplies:

all such rooms, as well as the UPS rooms themselves, must have suitable warning signs at their entrances;
all apparatus and socket outlets served must have signs readily identifying them as such;
these must have an accessible and identifiable means of isolation for all of the sockets served which must be separate from that for any other distribution systems present;
which are 'stand alone' supplies, these must have an accessible and identifiable output switch;
all apparatus required to be so supplied must be plugged directly into the UPS sockets;
they must be suitably tested and maintained in accordance with the manufacturer's instructions.

Guidance

Particular care should be taken when working on systems where there is automatic provision of a second source of supply should the mains fail; so-called uninterrupted or uninterruptible power supplies (UPS). Detailed knowledge of such supplies is essential before work on the systems or circuits they serve is carried out as an output will continue to be present when the mains output is removed; the UPS, or any automatically switched standby supply, should be checked first to ensure it is fully isolated. Where standby mains systems are installed, check that provision has been made for:

full disconnection of loads from all sources of supply including stand-by or bypass supplies;
full labelling of the switching arrangements, including input, output and bypass;
clear indication that loads are fed from a UPS or automatic standby supply, both at the area isolator and at the loads themselves.

Where UPS systems are installed, the rooms and distribution systems they serve, and where necessary for safety reasons, individual apparatus, should be clearly indicated by means of appropriately designed and located warning signs. Such signs provide reminders for those who regularly work in the area and inform others (e.g. maintenance staff, emergency services) who may enter the area to carry out work on installations but who may not be familiar with the distribution circuits. Where there is more than one distributed feed from a UPS, each feed should be provided with an accessible and clearly identifiable isolator and the distribution sockets should be labelled as to which feed they are attached.