Three pole, Four wire, Fusible mechanical interlock. 20 amp, 120/240VAC. 20A 3P4W 120/240VAC FUS MECH INT Legrand-Pass & Seymour http://www.legrand.us/product-detail/PassAndSeymour/IEC-309-Products/Fusible-NonFusibleMechanicalInterlock/Fusible-Mechanical-Interlock/20-Amp/PS420FMIR12W.pdf MECHANI