Model MP-100A is a damper actuator pack used to convert the WD-100 horizontal mount backdraft damper to motorized operation. These versatile motor packs feature power opening with spring return. The springs also provide damper closure in the event or electrical failure. MP-100A motor packs are supplied with mounting hardware, assembly instructions and actuator arms for either single or double panel installation. Rated for 115-230V. UL Listed.