Wiring Diagrams For Homes

wiringschematicsWiring Diagrams for homes is essential to your wiring projects. Knowing how electricity works and careful planning is essential for your safety, success of the project, and to ensure you have enough power with plenty to spare for future expansion.

Understanding basic-household-wiring is essential to tackling a wiring project safely. Knowing what each components function is, is a good place to start.

Beginning with the power to your home, it will arrive from the power company from overhead wires to a service head or from wires buried underground.

The service mast or head is that half mushroom looking thing where the wires connect on top of your house. The service head (Sometimes called a weather head) anchors the main wires.Three wires carry the standard 240-volt service to your home (two wires carry 120-volt current and one grounded neutral wire)

The electric meter, you know, that thing that measures how much power you use and mysteriously sends you a bill every month.

The main service panel or breaker box (old homes have fuse boxes) distribute power to all the individual circuits throughout the house. Each circuit has a fuse or breaker that can shut itself down in the even of a short or overload.

Safety Note: Wires that carry electricity from the service head to the electric meter and then to the main service panel are always live unless the power company shuts them off. If you feel there is a problem, call your power company, never attempt to service them yourself!

Electrical boxes are where you close any wire connections. The National Electrical Code requires connections, either spliced, to a switch, receptacle, or other device, be contained within a plastic or metal electrical box.

Switches control the current going to a light, ceiling fan, garbage disposal or other appliance or receptacles.

Receptacles sometimes called outlets provide the “plug-in” access to the power. 125-volt, 15-amp, three-prong outlets are the most common since 1965.

Grounding wire connects the entire system to the earth through grounding rods or metal water pipes. Electricity always seeks to complete a continuous circuit and return to it’s source. That path is provided by the (usually white) neutral wires that return the power current to the main service panel.

Wiring For Home Safety: Electricity always takes the path of least resistance. If you touch a device, tool, or appliance that is shorted out, the current could return to it’s source by passing through your body.

The introduction of a grounded system is designed to minimize this danger, providing a safe path for the current to follow back to it’s source. If you touch a short circuited device that is properly grounded your chances of getting a severe shock is greatly reduced.

Circuit Load Calculation For House-Wiring-Diagrams

Your house-wiring-diagram will help to determine if you need a larger main service panel. To do this, you are going to have to calculate the load on not only your existing circuits but your new ones as well. Calculating the supply and demand of your house is essential for creating a wiring-diagram for your home.

This planning process will ensure you have properly sized circuits for the lights, fixtures or appliances they supply. Once you know all the circuits you’ll need you can add them up to see if your existing main power supply is large enough or if you need a bigger one.

Make a list of each circuit to go along with your house-wiring-diagrams. This will help your electrician or inspector to determine if you need a larger main service panel.

Wiring Diagrams For Homes… Converting Amps/Volts/Watts

x Volts
Total Capacity Safe Capacity
15 A x 120 V = 1800 watts 1440 watts
20 A x 120 V = 2400 watts 1920 watts
25 A x 120 V = 3000 watts 2400 watts
30 A x 120 V = 3600 watts 2880 watts
20 A x 240 V = 4800 watts 3840 watts
30 A x 240 V = 7200 watts 5760 watts

When calculating supply and demand of a circuit first determine the safe capacity of that circuit, then calculate the load of all the lights, fixtures appliances etc… that will run on that circuit. This will tell you if you can add to an existing circuit, if an existing circuit is already overloaded, or how many new circuits you may need.

Find the safe capacity of a circuit by multiplying the voltage by the amperage, yielding the total capacity –  in watts. Then multiply the total capacities by 0.8 to find the safe capacity. Circuit breakers will have their amperage labeled on the switch or you will see it on the rim of the fuse. To determine the voltage, all single pole circuit breakers and plug-in fuses are 120v and double-pole breakers and cartridge fuses should be 240V.

Project Planning

Depending on the size of your project, consider all your power needs. For an addition or renovation, consider all possible ways a space might be used and plan for the electrical service to meet those needs.

Understanding how electrical service is provided will help you meet those different needs. For example, a 15 amp circuit provides adequate power for a spare bedroom but if you’re converting that space into a game room for your family, you will probably need a larger 20 amp circuit.

Now, is your main service capacity enough to handle the new load? Many older homes have a 60 amp service and need to be upgraded to at least a 150 amp service. If you need to upgrade you main service capacity, a certified electrician will need to complete this work! Map out what you plan to do and then get a recommendation as to how large the new main service panel should be.

When I added on and renovated my kitchen, I created a house-wiring-diagrams which told me my main service panel was too small to handle the new circuits. Knowing this, I had my electrician install a 200 amp panel. This was enough to handle all my additional circuits, a new sub panel in my garage and I’ve still got plenty of room for expansion.

Do yourself a favor and pre-purchase the service panel from your local home store and have your electrician install it. This will save you some money since the electrician is sure to mark it up if he purchases it. Home Depot and Lowes have experts in the electrical department to help with the purchase. Just tell them you’re upgrading your main service panel and you want to pre-purchase the panel for the electrician to install.

The wiring-diagrams for homes, planning process isn’t too complex but it is necessary if your project requires permits, which require inspections. Follow the steps below to flow through the process:

House-Wiring-Diagrams & Mapping Your System


When planning a new project, it’s easier (and safer) if you create an up-to-date map of your existing circuits. A House-wiring-diagrams or circuit map shows all of the lights, switches, receptacles, and appliances connected to each circuit. This map will also enable you to correctly label each circuit breaker on your panel door so the correct circuit can be shut off during repairs.

  • Create a sketch each room in the house on graph paper. Don’t forget the hallways, basement, attic, outside circuits and utility areas like the garage . Old blueprints of your home work great if you’ve got one.
  • Now, locate all electrical devices (mentioned above) including doorbells, thermostats, heaters, fans, and air conditioners. Use the electrical symbols key to help minimize clutter on your sketch.
  • Label each circuit at the main service panel with masking tape or label. Turn every circuit breaker off and then turn on one circuit breaker on at a time and see which switches, receptacles, fixtures and appliances are affected. Note the amperage at
    each circuit breaker.groundfaulttester
  • Turn on switches, lights, appliances, etc… to identify which ones are powered by that particular circuit. Now label each device with blue painters tape with the circuit number and amperage rating of the circuit breaker.
  • Make sure to test receptacles for power. A ground fault detector works great for this. Also, check both halves of the receptacle since they may be wired on different circuits or controlled by a switch.
  • Now you can label each circuit on the main service panel door with a summary of each circuit. Complete the house-wiring-diagrams and turn on all the circuits.


As you can see, creating a simple house-wiring-diagram is pretty simple.