Running Both Air Conditioners On 30 Amp System

Always looking for simple and inexpensive. My generator is wired so that it runs the house power off of its 30 amp breaker and includes the rear A/C unit. The front A/C unit is wired to a separate 20 amp breaker. So I simply put a transfer switch on the 20 amp line to A/C unit and installed a box beside it with a plug for an extension cord. You have to set two switches and plug in the cord to a separate 20 amp circuit. Cost < $30.