Zebra Instruments , # ZAPPRO / ZAP-PRO Plug-in Surge & Spike Protector (120 - 240V) Factory Warranty only available from Airstar Supply , the ONLY Approved Zebra Instruments Vendor Plug-In Transient, Surge, Lightning, & Spike Protection for 120-240 Volt Condensing Units and Furnaces. (Full instructions with photos in package.) "The most common cause ofCircuit Board componentfailure is damage as a result of poorly conditioned voltage." This unit works with either 120v or 240v.