Most Cytec switching systems have an AC selectable power entry module on the rear panel with a  dual-fuse holder, voltage selector and 2-pole rocker (on/off) switch. The fuse holder can be flipped to select either 110-120V or 220-240V. The picture shown is fused for 110-120V as indicated by the arrow pointing to the bar on the module casing. The fuse holder ships with both fuses even if the switch will only ever be used for one setting.  Note: There are some systems that use universal input switching supplies that accept 90 to 260 VAC and are fused accordingly.