“Voltage and frequency independent” UPS in compliance with IEC 62040-3, as well as online or double conversion, offers superior protection against problems in the power supply. Here, the input voltage is fed to a rectifier, with output being supplied by an inverter. Under normal operating conditions, the inverter receives its supply directly from the rectifier, when the power supply fails it is supplied directly from the batteries. Consumers have no direct connection to mains AC power supply; the UPS protects them from all power grid problems. In critical situations and with sensitive equipment, protection by VFI technology is highly recommended.