Planning or renovating the electrical system in your home starts with a wiring diagram. A good diagram shows every circuit, every outlet, every switch, and how they all connect back to the service panel. Whether you are building a new home, finishing a basement, or just trying to understand what is behind your walls, this guide covers the fundamentals of residential electrical wiring.
How Home Electrical Systems Work
Your home's electrical system starts at the utility transformer on the pole (or pad) outside. From there, the service entrance cable brings power to your meter, then to your main service panel (breaker box). The panel distributes power through individual circuits to every room in your house.
The Service Panel
The service panel is the heart of your home's electrical system. A typical residential panel receives 200-amp, 240-volt service through two hot legs (each 120V relative to neutral) and a neutral conductor.
Inside the panel:
- Main breaker: Controls all power to the panel. Rated at the total service capacity (100A, 150A, or 200A).
- Branch circuit breakers: Each protects an individual circuit. Single-pole breakers provide 120V for lights and outlets. Double-pole breakers provide 240V for large appliances.
- Neutral bus bar: All neutral (white) wires connect here.
- Ground bus bar: All grounding (bare or green) wires connect here.
Circuit Types
15-Amp Circuits (14 AWG wire)
- General lighting
- Bedroom outlets
- Living room outlets
- Most switch circuits
20-Amp Circuits (12 AWG wire)
- Kitchen countertop outlets (two dedicated circuits required)
- Bathroom outlets
- Laundry room outlet
- Garage outlets
- Outdoor outlets
- Dining room outlets
Dedicated Circuits
Some appliances require their own circuit, not shared with any other outlet or device:
- Refrigerator (20A, 120V)
- Dishwasher (20A, 120V)
- Microwave (20A, 120V)
- Garbage disposal (20A, 120V)
- Washer (20A, 120V)
- Electric dryer (30A, 240V)
- Electric range/oven (40-50A, 240V)
- Central air conditioner (30-60A, 240V)
- Electric water heater (30A, 240V)
- Furnace (15-20A, 120V)
- Sump pump (20A, 120V)
Room-by-Room Wiring Guide
Kitchen
The kitchen has the most demanding electrical requirements of any room.
Required circuits (NEC):
- Two 20A small-appliance circuits for countertop outlets (GFCI protected)
- Dedicated 20A circuit for the dishwasher
- Dedicated 20A circuit for the refrigerator
- Dedicated 20A circuit for the garbage disposal
- Separate lighting circuit(s)
Outlet placement:
- Countertop outlets every 4 feet (no point on the countertop more than 2 feet from an outlet)
- GFCI protection required for all countertop outlets and outlets within 6 feet of a sink
- Outlets at counter height (42-48 inches from floor) or just above the backsplash
Lighting:
- General ceiling light (15A circuit)
- Under-cabinet task lighting
- Consider separate circuits for general lighting and task lighting
Bathroom
Required circuits:
- Dedicated 20A circuit for the bathroom outlet(s) -- GFCI protected
- If multiple bathrooms, they may share a single 20A circuit, but a single bathroom cannot share its outlet circuit with any other room
- Lighting can be on a general lighting circuit
Key requirements:
- All outlets must be GFCI protected
- At least one outlet within 36 inches of each sink
- Vent fan on its own switch (often combined with a timer switch)
- Heated floor (if installed) on a dedicated circuit with GFCI protection
Living Room / Family Room
Typical circuits:
- One or two 15A general outlet circuits
- One 15A lighting circuit
- Outlets on walls every 12 feet (no point along a wall more than 6 feet from an outlet)
- Floor outlets for rooms wider than 12 feet (to avoid running cords across walkways)
Switch placement:
- 3-way switches at each entry point for overhead lights
- Consider dimmer switches for ambient lighting
Bedrooms
Typical circuits:
- One 15A outlet circuit per bedroom (or two bedrooms sharing a circuit)
- Lighting on a general lighting circuit
- Outlets every 12 feet along walls
- At least one outlet on each wall
Code requirements:
- All bedroom outlets must be Arc Fault Circuit Interrupter (AFCI) protected (2014 NEC and later). This requires either AFCI breakers or AFCI outlets.
- At least one wall switch controlling a light fixture or a switched outlet
Garage
Required circuits:
- At least one 20A circuit for outlets -- GFCI protected
- Dedicated circuit for garage door opener
- Separate lighting circuit (consider motion-activated lights)
Key considerations:
- GFCI protection required for all garage outlets
- If you plan to use power tools, consider a dedicated 20A circuit for the workbench area
- A 240V outlet for a welder, compressor, or EV charger may be needed
Laundry Room
Required circuits:
- Dedicated 20A outlet for the washing machine
- Dedicated 30A/240V outlet for an electric dryer (or gas dryer on 120V)
- GFCI protection required for the washer outlet (2014 NEC and later)
Outdoor / Exterior
Required circuits:
- At least one 20A GFCI-protected outlet at the front and back of the house
- Outdoor lighting on a separate circuit
- Hot tub, pool equipment, or EV charger on dedicated circuits
Key requirements:
- All outdoor outlets must be GFCI protected
- Outlets must have weather-resistant (WR) covers
- Underwater pool lighting requires specific GFCI and bonding requirements
Planning Your Wiring Diagram
Step 1: Draw the Floor Plan
Start with a basic floor plan showing walls, doors, and windows. You do not need architectural precision -- a rough layout with correct proportions is fine.
Step 2: Place Outlets and Switches
Mark the location of every outlet, switch, and light fixture on the floor plan. Follow NEC spacing requirements:
- Outlets every 12 feet along walls (6-foot rule from any point)
- Switches at every room entry
- GFCI outlets where required (kitchens, bathrooms, garages, outdoors)
Step 3: Assign Circuits
Group outlets and lights into circuits. General rules:
- Maximum 10 outlets or lights per 15A circuit
- Maximum 13 outlets per 20A circuit (practical recommendation; code varies)
- Do not mix lighting and outlet circuits in kitchens or bathrooms
- Label each circuit with a number that corresponds to its breaker
Step 4: Draw Wire Runs
Show the wire path from the panel to each outlet and switch. In practice, wires run through the attic or crawlspace and drop down to each box. Mark the wire gauge (14 AWG for 15A, 12 AWG for 20A).
Step 5: Panel Schedule
Create a breaker schedule showing:
- Breaker number and size
- Circuit description (e.g., "Kitchen countertop outlets")
- Wire gauge
- Room served
Using a tool like CircuitDiagramMaker makes this process dramatically faster. You can drag outlet and switch symbols onto your floor plan, draw wire runs with color coding, and label every circuit. The tool calculates your panel schedule automatically.
Circuit Sizing and Breaker Selection
How to Size a Circuit
The NEC limits continuous loads to 80% of the breaker rating:
- 15A breaker: 12A continuous load maximum
- 20A breaker: 16A continuous load maximum
Example: A kitchen countertop circuit with a toaster (1,200W), coffee maker (900W), and blender (400W):
- Total watts: 2,500W
- Amps at 120V: 2,500 / 120 = 20.8A
- This exceeds a single 20A circuit. You need two 20A circuits with the appliances split between them.
Wire Gauge and Breaker Matching
| Breaker Size | Wire Gauge | Typical Use |
|---|---|---|
| 15A | 14 AWG | General lighting, bedroom outlets |
| 20A | 12 AWG | Kitchen, bathroom, garage, laundry |
| 30A | 10 AWG | Electric dryer, water heater |
| 40A | 8 AWG | Electric range |
| 50A | 6 AWG | Electric range, large sub-panel |
| 60A | 4 AWG | Sub-panel feed, central AC |
Never use a wire gauge smaller than what the breaker requires. Using 14 AWG wire on a 20A breaker is a fire hazard -- the wire can overheat before the breaker trips.
Common Code Requirements (NEC Summary)
- GFCI protection: Required in kitchens (within 6 feet of sink), bathrooms, garages, outdoors, crawlspaces, unfinished basements, laundry areas, and boathouses.
- AFCI protection: Required in bedrooms, living rooms, dining rooms, family rooms, hallways, closets, and similar rooms (2014 NEC and later).
- Tamper-resistant receptacles: Required in all dwelling unit locations accessible to children (2008 NEC and later).
- Weatherproof covers: Required for all outdoor outlets -- "in-use" covers that protect even when a cord is plugged in.
- Neutral in switch boxes: Required in all new switch boxes (2011 NEC and later) to support smart switches and occupancy sensors.
Always check your local building codes, as they may amend or add to the NEC requirements. Some jurisdictions are on older NEC editions.
Common Wiring Mistakes
- Overloading circuits. Putting too many outlets on one circuit leads to tripped breakers and potential fire hazards.
- Wrong wire gauge. Using 14 AWG wire on a 20A circuit is a code violation and a fire risk.
- Missing GFCI protection. Failing to install GFCI outlets where required is both a safety risk and a code violation that will fail inspection.
- Backstab connections. Pushing wires into the back of an outlet (backstab) instead of wrapping them around the screw terminals creates unreliable connections that can arc and cause fires.
- No junction box. All wire splices must be inside an accessible junction box. Splices buried in walls are a serious code violation.
- Crowding the panel. Not leaving space for future circuits. Plan for at least 20% spare capacity.
Plan Your Home Wiring with Our Free Tool
CircuitDiagramMaker gives you everything you need to plan your home's electrical system:
- Drag and drop outlets, switches, GFCI outlets, breakers, and light fixtures
- Draw wire runs with proper color coding (black, white, red, bare)
- Label every circuit with breaker numbers and descriptions
- Automatically generate a panel schedule
- Export your diagram as a PDF for your electrician or inspector
- Share a link so your electrician can review your plan before starting work
Plan your home wiring with our free tool
Key Takeaways
- Your home electrical system flows from the utility to the meter, to the main panel, to individual branch circuits.
- Kitchens, bathrooms, and laundry rooms have the most specific code requirements, including dedicated circuits and GFCI protection.
- Match wire gauge to breaker size: 14 AWG for 15A, 12 AWG for 20A, and heavier gauges for 240V appliances.
- Follow NEC outlet spacing rules: no point along a wall should be more than 6 feet from an outlet.
- AFCI protection is now required in most living spaces; GFCI protection is required in wet or damp locations.
- Plan your wiring diagram before starting work -- it saves time, catches mistakes, and satisfies inspection requirements.
Originally published at https://circuitdiagrammaker.app/blog/home-electrical-wiring-diagram-basics.
