I'm confused as I thought all 240 volts had 4 prongs. I'm thinking you may be receiving power from one power leg rather than both, something to look into. If you get the correct connector straight, you may want to consider an Interlock rather than a transfer switch. I originally was going with a Transfer Switch but decided on an Interlock. With a simple Interlock device, you power whatever you wish in your breaker panel by turning the breakers on, careful not to overload the generator, plus it's less expensive. The Interlock prohibits you from having the Main Breaker on when generator is on. With Transfer Switch, you power only the selected breakers that are wired to it. Lastly, when running 240 volts, the generator should be balanced, that is, not excessive wattage on one power leg versus the other. Just bought a watt meter to help with the balance, and the watt meters are also available at Reliance. I got the one for 30 amps and couldn't locate one any place else. Special order for exterior use but mine was shipped same day ordered.