Absolutely!! They are made to work both ways. Here's a link to the exact timer I use on my main filters: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 There are instructions included for wiring it "backwards" but essentially, the white wire goes to the silver terminal on your outlet. The black wire goes to the terminal on the switch marked "Load 2 In." Then another black wire is attached to the "Load 2 Out" terminal on the switch and is attached to the black (brass) terminal on the outlet. Your pump/filter/or whatever is plugged into the outlet. The switch is spring loaded and can be set for anywhere from 15 minutes to two hours. Then the circuit is closed and the pumps or whatever come back on. We've been using these for years and they are awesome.