The hardware is normally powered by the mains, the UPS only taking over in the event of a mains power cut or major drop in voltage.

Off Line technology enables the protected appliances to be powered for long enough to save data and/or turn off the appliances correctly.

This switch over to battery power takes a little time (generally >4ms) which will not disturb computers with cutting power supplies, but it may cause a problem for more sensitive hardware (measurement instruments).

Off Line UPSs are the most cost effective. They are recommended for single station computers (PC-type) designed for office automation or games and small servers in an environment with little electrical disturbance such as an urban area.

The principle of Off Line technology is improved since the input voltage is monitored and filtered by the UPS before being fed to the equipment.

The power supplied is therefore a higher quality. A voltage regulator enables quality power to continue to be supplied during major variations and without using the batteries whose useful life is directly proportional to the number of recharging cycles. A filter and surge protector increase the security.

When there is a power cut, the UPS switches to battery mode (switch over time <2ms) and a communication software takes charge of saving files and closing down programmes.

Line Interactive technology is recommanded in areas in which the mains supply is moderately disturbed (commercial zones or rural areas) and also chosen to protect servers, CAD applications and minor accounting tasks .

A permanent source of power is supplied by the UPS thereby ensuring a constant voltage and no interference. The appliance to be protected is therefore totally disconnected from the mains which means no switch over time and no power line disturbances.

In the event of a mains power failure a communication software will automatically close down all the programmes after having carried out any necessary backups.

Tests prove that On Line UPSs offer the most stable output voltage and the best immunity to interference.

On Line technology is particularly recommended in industry . It is also chosen to protect systems in which even the smallest loss of data is inacceptable, such as calculators, automatons, cash registers, major IT systems for example and more generally, any strategic applications, sensitive electronic systems and medical apparatus .