Applying Capacitor Contactors

Capacitor contactors are used when switching a single step or multi step capacitor or condenser bank. They are required due to the very high inrush current (up to 60 x In) caused by energizing a capacitor. The LS Electric capacitor contactor units mount directly to the applied contactor. They consists of a dampening resistor which absorbs the high current to prevent contactor damage. This is standardized in IEC60947-4941, UL, and CSA.

Contactor with AC-9 unit mounted on the front.

Schematic

Sizing and Selection

Selecting a contactor for a capacitor switching application requires knowing the kVar. LS Electric offers capacitor contactor units for up to the MC-100a frame. For higher ampacities you can oversize the contactor. Use the below Tables for easy selection.

Contactor with Capacitor unit

Contactor only

- Capacitors must be discharged (<50V) before the contactor is closed.

- To prevent short circuit current, fuse must be 1.5-2 times the rated current.