Contactors are similar to relays in that they behave like remote switches, but are designed specifically for high current applications in power management. As such, unlike relays, they are typically used in a normally open (NO) position and are generally larger in size. Though most contactors provide the same switching function, they are typically configured for specific conditions.
Whether you require a contactor for a starter motor or as part of a more complex power control device, there are a number of important factors to consider when making your selection. Variables such as the AC number, coil voltage and power ratings will all have to be considered to be sure that the contactor is compatible with the intended device or system. It is also important to check if the contactor is certified with appropriate industrial standards.
Although they can be used as stand-alone hardware control gear such as push-button controllers, auxiliary contacts are typically internal components of a contactor and are used to reduce current power in high voltage applications. A range of auxiliary contacts is available to compliment your contactor solution.
Altivar Variable Speed Drives from Schneider Electric