Handbook of Electrical Installation Practice - BeKnowledge

Standby Power Supplies 155
Fig. 6.19 Modern UPS systems need to be designed for the office environment. They need
to be compact, easy to use, quiet and stylishly designed. The unit shown is a
500VA on-line UPS, which at full load provides 15 minutes back-up power –
enough time to complete important tasks, save data and perform an orderly
shutdown. Battery extension packs can be added to extend the duty period up
to several hours running time.
The floor area, or footprint, of the unit is an important aspect. In the lower-power
market, the newer systems employ a ‘tower’ design and are small enough to sit conveniently
under a desk (Fig. 6.19). For larger systems, the weight and hence the floor
pressure exerted by the units is an important considerattion – some floors may
require strengthening with steel joists to prevent the UPS and batteries falling
through them.
Manufacturers of low-power UPS units have benefited from improved, lower-cost
power transistors and more reliable sealed, rechargeable batteries.
UPS systems are coming out of the plant room and are used more and more in
the place of work. This means they ought to blend in with the ‘high-tech’ image of
modern offices and not look like a smaller version of an industrial plant UPS. A
range of on-line UPS systems ranging from 1kVA to 5kVA output rating is shown
in Fig. 6.20.