NEMA 5-20P to L14-30R Plug Adapter - 1 Foot, 20A/125V, 12 AWG - Iron Box # IBX-5184-01 NEMA 5-20P Plug to L14-30R Connector 1 Foot Length 12/3 AWG, SJT Jacket Rated for 20 Amps, 125V Wried to energize both sides of your auto-transfer switch