Choosing the right size of a wire in terms of thickness and length is important in electrical installations as it determines the maximum amount of current a conductor can carry through it safely. For this reason, always choose appropriately sized wires for every electrical wiring. Wire gauges indicate the size of wires and their corresponding maximum current capacity to make choosing the right wire easier. United States uses the American Wire Gauge standard (AWG standard) to classify wires into different sizes.
Read the manual to determine the amperage of the appliance for which you are installing the wire. The wire size you will choose is required to meet the constraints for the power rating of the appliance--for example gauge twelve sized wires are required for various heater circuits and kitchen receptacles.
Search a wire gauge table for the maximum amperage of the circuit through a particular circuit breaker. The amp rating for the circuit breaker also dictates the wire gauge as well. Wire gauges determined by circuit breaker amp ratings less than 30A correspond to the wire gauges depending on the appliance amp rating. However, wire gauges for ratings above 30 amps differ from each other for circuit breakers and appliance rating.
Determine the total amps necessary to power the entire circuit if it has more than one appliance connected to it such as a number of light bulbs or outlets. Add up the watts for all the appliances in the circuit and divide the sum by the voltage of the current, duly noted on the electric meter for the house. Refer the quotient to the wire gauge chart and determine the wire gauge necessary for the circuit. Once you size the required wire according to its gauge, it makes it easier to select the right one from an electrical supplies store.