Basic Understanding of Electrical House Wiring

Most if not all of us have our houses wired for electricity and with some basic understanding it can remove some of the mystery that surrounds it.  This write-up will be focused on how things are done in the US.  The principles will transfer to other countries, but the details will be different.  Also it is important to note this is not enough information to qualify you to start poking around in the electrical circuits in your house.

In the united states residential electrical service brings 240 volts to the house with the capacity of somewhere between 100 to 400 amps.  Think of voltage as the pressure and amps (also called current) as the amount of electricity.  This service is connected to a distribution panel that has circuit breakers that provide electricity to all the circuits in the house.  Most of these circuits are 15 amps and 120 volts.  Kitchens and bathrooms will have 20 amp, 120 volt circuits due to the fact that they usually have devices that draw more current like blow driers, curling irons, toasters and microwaves.  High power devices like electric ranges and electric clothes driers require dedicated circuits of 240 volts.

The service coming into the house has two legs and a common.  The voltage between the two legs is 240 volts and between either leg and the common is 120 volts.  Your service panel will split this 240 volts between two sides of 120 volts each.  If you need 240 volts the circuit breaker will bridge between both sides to get 240 volts.  A good electrician will try to balance the loads between these two sides, you should never see most of the breakers on one side of the service.

The way a house is wired the “common” or “neutral” is the white wire and it should never be run through a switch.  It is electrically the same as the ground wire.  If you open up your service panel you will see all the white wires and bare wire attached to a common bus (usually a copper bar with screw terminals).  The bare wire braid coming into the house will also be attached to this.

Each circuit is a black wire and it is attached to a circuit breaker that limits the amount of current that can flow into the wire.  The gauge of the wire (how thick it is) determines how much current it can safely handle and if it is exceeded the breaker trips and shuts off the circuit.  This can happen if you turn on too many thing on the same circuit or if some kind of fault happens in the wiring.  If the breaker doesn’t protect the circuit the wiring could overheat and cause a fire.

Further anyplace there is the chance of water being near the plug you will need to have the circuit going through a Ground Fault Circuit Interrupt (GFCI).  This will either be the first plug-in the circuit in the wet area (which will protect all the plugs that come after it) or the breaker itself can have the GFCI protection.  This device monitors the current flowing on each side of the circuit and if there is a difference it will trip and cut off the electricity.  This fault conditions occurs when the electricity finds another path to ground, which is almost universally bad and this device protects you from a getting a shock.

The standard convention in the us is that 14 gauge wire that handles 15 amps is in a white sheath of insulation, yellow if for 20 amp circuits and orange is for 30 amp circuits.  You will see this wire denoted as:

  • 14-2 which is 14 gauge wire with 2 insulated wires(colored white and black) and a bare ground wire.
  • 14-3 which is 14 gauge wire with 3 insulated wires (colored white, black and red) and a bare ground wire.  This is used for 3 and 4 way switched circuits.
  • 12-2 which is same as 14-2 except the wire is thicker 12 gauge.
  • And so on

Note that electricity can kill you and this is intended for information purposes only.  You need to know a lot more that is described here before you start messing around with the electrical circuits in your house.

Author: Jerry Ward

Working on creating a 10 acre urban homestead in S.E. Michigan. To pay the bills I work as a product manager/business analyst in the IT field. Now the admin of Save Our Skills