Attached Garage Wiring Code - Electrical - DIY Chatroom Jan 02, 2011Attached garage wiring code. We just had a building put up (40x50) about 5 feet off our house. It was wired by an electrician who knows it will be connected to out house next spring with a breezeway. He went from out 200 amp main service into the new building with 3 large wires and installed a 100 amp service in the new garage. Electrical Wiring for an Attached Garage - Ask the Electrician Planning Circuits for Wiring an Attached Garage Electrical Question: I Need to run a circuit to the attached garage to accommodate an electric heater of 5000 watts (17,000btu) and it needs a 240 circuit. I also am splitting the lights/outlets currently in the garage into at least two breakers to take load off of the single breaker that feeds the garage today (and actually part of the den).