How to Map Out Electrical Wiring Circuits for a New House

Multiply the length of the house by its width. This determines the square footage as defined by the National Electrical Code for determining the electrical circuit requirements.

Divide the square footage by 600 and round any fractional result up to the next highest number. The result is the minimum number of lighting circuits required by National Electrical Code. Lighting circuits include permanently wired lights, lamps controlled by switches and general-purpose convenience receptacles. Convenience receptacles supply vacuum cleaners, nightstand lamps or other small appliances.

Mark each room with a lighting circuit number that indicates which circuit supplies the room's lights and receptacles. Circuits usually supply more than one room. For example, if three bedrooms and a hallway total 600 square feet, they can share one lighting circuit. Mark the rooms "L1" to indicate that "lighting circuit one" supplies those rooms. The kitchen, dining room and living room total another 600 feet and share "lighting circuit two" indicated by "L2" on the map.

Locate the rooms served by the small appliance circuits. A minimum of two small appliance circuits wired with 12-gauge wire and served by 20-amp circuit breakers are required for a kitchen and pantry. Mark these in the kitchen and pantry with "SA1" and "SA2." These circuits may not supply lighting or other outlets, except for one wall-mounted clock and one gas-range receptacle.

Map additional 120-volt appliance circuits in the rooms where they are required. These include laundry receptacles, bathroom receptacles and refrigerator or freezer receptacles.

Indicate the rooms that require individual 240-volt appliance circuits. Mark each circuit with its own letter or code. The electric range might be "R" in the kitchen, while an electric dryer might be "D" in the laundry room.

Write each circuit code on the side of the floor plan followed by it's current requirements. Lighting circuits are 15-amp circuits, small appliance circuits are 20 amps. Other appliance circuits have different current requirements. An electric range is 240 volts at 50 amperes, while a refrigerator is 120 volts at 15 amperes.