An uninterruptible power supply for providing AC power to a load, the uninterruptible power supply comprising: an input to receive AC power from an AC power source; an output that conveys AC power; a DC voltage source that provides DC power, the DC voltage source having an energy storage device; an inverter operatively coupled to the DC voltage source to receive DC power and to provide AC power; a transfer switch constructed and arranged to couple one of the AC power source and the inverter to the output of the uninterruptible power supply; and a chassis for housing at least the DC voltage source, inverter, and transfer switch, the UPS being characterised in that the chassis comprises: a first "L" shaped panel; a second "U" shaped panel constructed and arranged to mate with the first panel to define an enclosure with an open end; a third panel constructed and arranged to mate with said first and second panels to close said open end of said enclosure, and a first fastener securing the first panel and the second panel into a substantially fixed configuration by securing the third panel to one of the first and second panels (12, 14), wherein at least one of the first and second panels (12, 14) further comprises a support structure constructed and arranged to hold at least one of the DC voltage source, inverter, input, output, and transfer switch in a substantially fixed position. an input to receive AC power from an AC power source; an output that conveys AC power; a DC voltage source that provides DC power, the DC voltage source having an energy storage device; an inverter operatively coupled to the DC voltage source to receive DC power and to provide AC power; a transfer switch constructed and arranged to couple one of the AC power source and the inverter to the output of the uninterruptible power supply; and a chassis for housing at least the DC voltage source, inverter, and transfer switch, the UPS being characterised in that the chassis comprises: a first "L" shaped panel; a second "U" shaped panel constructed and arranged to mate with the first panel to define an enclosure with an open end; a third panel constructed and arranged to mate with said first and second panels to close said open end of said enclosure, and a first fastener securing the first panel and the second panel into a substantially fixed configuration by securing the third panel to one of the first and second panels (12, 14), wherein at least one of the first and second panels (12, 14) further comprises a support structure constructed and arranged to hold at least one of the DC voltage source, inverter, input, output, and transfer switch in a substantially fixed position. a first "L" shaped panel; a second "U" shaped panel constructed and arranged to mate with the first panel to define an enclosure with an open end; a third panel constructed and arranged to mate with said first and second panels to close said open end of said enclosure, and a first fastener securing the first panel and the second panel into a substantially fixed configuration by securing the third panel to one of the first and second panels (12, 14), wherein at least one of the first and second panels (12, 14) further comprises a support structure constructed and arranged to hold at least one of the DC voltage source, inverter, input, output, and transfer switch in a substantially fixed position.