The 100-D140H00 contactor is an Allen-Bradley Bulletin 100-D series contactor. It is fitted with a conventional coil with a 208 Volts AC voltage rating. The contactor works like an electrically-controlled switch and it is controlled by the coil. The switched circuit carries a much higher power level than the power level carried by the contactor coil. The 100-D140H00 contactor is part of the Bulletin 100-D product line and it is suitable for switching 3-phase and 1-phase AC motors. Contactors like this one are also widely used for lighting applications. Contactors are similar to relays in that they are both used for switching circuits. However there are differences between the 2 types of devices in that a contactor is used for repeatedly establishing or interrupting an electric circuit, and a relay is a device through which contacts in one circuit are operated by an alteration in the conditions in the same circuit.

Another difference is that relays are more commonly used in single-phase circuits, and contactors like the Allen-Bradley Bulletin 100-D series 100-D140H00 contactor are commonly used for switching 3-phase loads. A third major difference is that relays are rated for up to 250 Volts and contactors are rated for up to 1000 Volts. The 100-D140H00 contactor has 3 poles but it does not have any auxiliary contacts. The current rating of the 100-D140H00 contactor is 140 Amps. The contactor should be switched off and disconnected from the power before any maintenance work is carried out. Only original spare parts and accessories should be used for the replacement of faulty or malfunctioning contactor parts. The 100-D140H00 contactor should be checked immediately after the occurrence of any short circuits that it experiences. Minor contactor welds that are caused by short circuits can be removed by using a screwdriver to separate them.