Compatible Models：QYZZRS Generator Interlock Kit Compatible with Thomas & Betts, Challenger 150 or 200 Amp Panel. Interval Space Required：1 TO 1 1/8 Inch Spacing Between Main and Branch Breaker. Installation Note: Before installing the interlocking kit, Attach the screws to the interlock kit first. Let's simulate the use of the test, so that we can better align the installation position, to avoid errors in the installation position, resulting in failure to use. Safe use：The manual transfer switch device allow portable generator safe back feeding power supply to distribution panel and home line. Prevent utility and generator supplies from being ON at the same time. Aren't putting electrician in dangerous and damage electric devices during power outages. Package：Our Generator Interlock kit include 1 × Interlock plate, 3 × Screws kit, 1 × Drill Bit, 1 × Instruction Bulletin, 2 × Generator Start-Up Procedure Label, 8 × Remind Label, 2 × Zip Ties. The manual transfer switch device allow portable generator safe back feeding power supply to distribution panel and home line. Prevent utility and generator supplies from being ON at the same time. Aren't putting electrician in dangerous and damage electric devices during power outages.