To achieve a large capacity system at low cost, the PLZ1004W has an expandable option PLZ2004WB as a booster unit. Using 1 PLZ1004W as a master unit, a maximum of 4 booster units can be parallel connected. (Max. 9kW, 1800A) Note: PLZ2004WB(Booster unit) can be used for the PLZ1004W only. It cannot be connected and used with any other model.