Breaker interlock kit. Buy a UL rated device that fits your specific breaker box. These have been tested and validated to work. Many insurance companies and jurisdictions require the UL rating. 30 Amp 2 pole (double) breaker.Again you will need to buy one that fits your breaker box. All ...
it may be false economy to attempt to build one. There are other solutions out there, one is an interlock system that you can get for your house breaker panel, it creates an interlock system where your main breaker must