How to choose a suitable wire size for your residential electrical applications?
Choosing a suitable wire size for your AC appliances whether supplying power to an appliance, connecting circuit breakers or a solar PV system has significant benefits to the safety and performance of your installation, namely:
- ensures your appliances receive sufficient voltage to operate satisfactorily
- minimises wastage of energy resulting from wire resistance
- prevents stress and damage to the wire insulation.
How do you select a wire size
The wire size used for an appliance depends on the appliance load current (amps), supply voltage and length of that wire or cable that will carry the current. Larger appliances draw more current therefore need larger diameter wires (lower gauges) to minimise voltage drop.
Indicative wire sizes for selected household appliances (air-conditioners, heaters, stoves, fridges, microwave and others)
|Wire size (AWG)||Wire size (sq.mm)||Wire size (mm)||Current rating and Voltage||Appliances
|18-22||0.823 - 0.326||1.024 - 0.644||Thermostats, door bells, security systems, garage opener
|16||1.31||1.29||Light duty extension cords
|14||2.08||1.63||15A/120V||light fixtures (1~ 100W) , sockets/receptables/ house outlets - TV, stereo, computer, light electronics
|12||3.31||2.05||20A/120V||Light fixtures (400,600, 800 watt lamps), sockets/receptacles, microwave,fridge, electric kettle
|10||5.26||2.59||30A/240V||window air-conditioner, washing machine, clothes dryer, water heater, dish washer
|8||8.37||3.26||40A/240V||Central air conditioner, electric range, oven
|6||13.3||4.11||55A/240V||Central air conditioner,electric furnace
*Adapted from Black and Decker: Complete Guide Domestic wiring . Note: The wire sizes are specific to NM (non-metallic sheath) type wire, ambient temperature 30°C
How to find an indicative wire size based on a current rating
Some times, you have an appliance’s current rating (amps) and want to find an indicative wire gauge that can carry that current.
For example, you need to find a wire size for a 20 amp circuit for your air-conditioner.
You can also use the calculator below to find indicative wire sizes that can safely carry a specified current. It works for both copper and aluminum conductors.
Note: Calculator is based on NEC 2017, ampacities of two or three insulated conductors, and assumes 0 to 2000 Volts with an ambient air temperature of 30°C (86°F)*, conductor temperature of 60°C.
For example, using the calculator, to carry 50A , the minimum wire size for copper is 4 AWG while 1 AWG for 100A.
How to find wire size to safely carry a specified current (amps) over given length
Longer cable runs under load may experience significant voltage drops if not sized properly. Appliances connected at the end of the cable run may not operate properly because of a lower than expected voltage drop.
You can use the calculator below to find a wire size to carry a load current over a given length.
Wire resistances used are based on NEC 2017, Table 9 Alternating-Current Resistance and Reactance for 600-Volt Cables, 3-Phase, 60 Hz, 75°C (167°F) — Three Single Conductors in Conduit
For example, if you wanted to find a wire size to safely carry 30A over 200 feet. Working with a maximum voltage drop of 3% for a branch circuit, at a voltage of 240 V, the minimum cable size is 6 AWG and final voltage drop would be 232.8A.