Square D EIK40602 Electrical Interlock Switch Kit Brand: Square D. Part Number: EIK40602. Square D Electrical Interlock Switch Kit, For Use With: Heavy Duty Safety Switch. Additional Description: SQD -EIK40602 KIT ELECTRICAL INTERLOCK SWITCH. Catalog Description: Interlock, safety switch, 2 x NO, 2 x NC contact, heavy duty series E4-E5 400A to 1200A..