The main limitation to controlling dust collectors is the start up current surge - not the running current. In many cases the start up current can be as much as four to five times the running current and last for several seconds. This initial surge can over time damage the contacts in the iVAC Dust Collection Switch Boxes. If you have a dust collector that requires power that exceeds the specifications of the either an iVAC Switch Box or a Pro Switch Box, the iVAC Contactor is the solution to this problem. The iVAC Contactor is basically a heavy duty 3 pole relay housed in an electrical box. Used with an iVAC Switch Box, the iVac Contactor has the ability to withstand start up currents of up to 150 Amps and then maintain a running current of up to 25 Amps. It is also rated to operate at up to 240v AC, either single or three phase, and has the ability to control dust collectors up to 7 HP. The use of a iVAC Contactor is strongly recommended for any dust collectors operating on 115v AC that are over 1 HP, and for any dust collector over 1.5 HP operating on 240 v AC. Imported NOTE: Because the installation of the contactor usually requires a custom connection, the installation must be performed by a certified electrician. The installation guide can be seen on the iVAC web site. iVAC Contactor Kit: Contains a Contactor; Electrical Box; an Interconnect Cable to the iVAC Switch Box or iVAC Pro Switch S11515NA and S11520NA; and a set of required Hardware. All electrical materials are UL certified. Specifications Electrical Box - Measures 8" x 8" x 4". UL E109311. Contactor Rating - 240V AC , Surge Current 150 Amps, Running Current 40 Amps, 3 Pole, Control Voltage 115V AC, UL E249187. Control Cable - 115V AC - 6 ft. long, UL approved.