An uninterruptible power supply system comprising: an input to receive input power having an input voltage; an output to provide output power; a neutral line; an automatic voltage regulation transformer coupled to the input and the output of the UPS and having an input, an output, a core and at least a first switch and a second switch, said first switch being controllably coupled to the core and the AVR transformer input and said second switch being controllably coupled to the core and the AVR transformer output characterised in that the UPS system further comprises: a bypass switch configured to selectively couple the core of the AVR transformer to the neutral line and a controller configured to control the first switch and second switch of the AVR transformer and the bypass switch, wherein the controller is configured to control the bypass switch to isolate the core of the AVR transformer from the neutral line in the first mode of operation and to couple the core of the AVR transformer to the neutral line in a second mode of operation; wherein the controller is configured to, in the first mode of operation, couple the first switch of the AVR transformer to the core and to the AVR transformer input and the second switch of the AVR transformer to the core and to the AVR transformer output in a configuration to provide an output voltage of the AVR transformer that is equal to an input voltage of the AVR transformer. an input to receive input power having an input voltage; an output to provide output power; a neutral line; an automatic voltage regulation transformer coupled to the input and the output of the UPS and having an input, an output, a core and at least a first switch and a second switch, said first switch being controllably coupled to the core and the AVR transformer input and said second switch being controllably coupled to the core and the AVR transformer output characterised in that the UPS system further comprises: a bypass switch configured to selectively couple the core of the AVR transformer to the neutral line and a controller configured to control the first switch and second switch of the AVR transformer and the bypass switch, wherein the controller is configured to control the bypass switch to isolate the core of the AVR transformer from the neutral line in the first mode of operation and to couple the core of the AVR transformer to the neutral line in a second mode of operation; wherein the controller is configured to, in the first mode of operation, couple the first switch of the AVR transformer to the core and to the AVR transformer input and the second switch of the AVR transformer to the core and to the AVR transformer output in a configuration to provide an output voltage of the AVR transformer that is equal to an input voltage of the AVR transformer. a bypass switch configured to selectively couple the core of the AVR transformer to the neutral line and a controller configured to control the first switch and second switch of the AVR transformer and the bypass switch, wherein the controller is configured to control the bypass switch to isolate the core of the AVR transformer from the neutral line in the first mode of operation and to couple the core of the AVR transformer to the neutral line in a second mode of operation; wherein the controller is configured to, in the first mode of operation, couple the first switch of the AVR transformer to the core and to the AVR transformer input and the second switch of the AVR transformer to the core and to the AVR transformer output in a configuration to provide an output voltage of the AVR transformer that is equal to an input voltage of the AVR transformer.