Gary, you're close. The transfer switch is a good choice. You also need the appropriate power cord and power inlet box to connect everything together.

We recommend this power transfer system for the Generac 17500 watt portable generator:

http://www.electricgeneratorsdirect.com/Generac-6296/p8535.html

Features include:

• Generator Main and Utility Main are mechanically interlocked preventing utility or generator power back feed.
• Full branch circuit protection with Siemens® circuit breakers.
• Dual watt meters help monitor and balance generator load, prolonging generator life.
• Pre-Assembled wire harness for easy connection to the load center.

Other Items Needed:

• New 2-pole, 240V Breaker to mount in main load center – amperage to match utility breaker (see specifications Table I for Utility Main Breaker size – should be manufactured by same as Main load center).
• Anchors and screws to mount switch to wall.
• PVC cement (to secure connectors onto flexible conduit)
• Additional wire connectors if switch is “hard-wired”. See Table 2 for correct size.
• May need Arc-fault, GFCI or Surge protection circuit breakers. If Arc-fault, GFCI or Surge protection circuit breakers are used as the branch circuit protector in the main load center, they MUST be used in the manual transfer switch. See Table 3 for compatible breakers.
• Power Inlet Box – for “hard-wired” installations.
• Power Cord to connect generator to switch or power inlet box.

Any 50A manual transfer switch will give you a maximum of 12,500 watts which is the same for the generator you purchased. The Generac GP17500E has a 50A outlet for its largest output which provides a maximum wattage capability of 12,500 watts. (Amps x Volts = Watts).