How to tell the difference between 110v and 220v

Updated April 17, 2017

Electricity is indispensible in our lives, delivered to our homes via transformers, and converted for residential use. Every home has two lines from the local transformer delivering current, and one line for returning current back to the transformer. The two lines that deliver power at 120 volts equal a total of 240 volts. There are some relatively fail-safe methods for identifying the difference between 110-volt and 220-volt wiring.

Identify the type of wires that are to be tested. If it is a fat cable with heavy gauge wire such as 6-3wg, it will be 240-volt. Otherwise, just looking at the cable will not be enough since the same type and size of wire can be used in both applications on occasion. When dealing with 120v, there will be one positive wire with current, a neutral wire and a ground. However, when dealing with 240v, there are two positive wires with current, a ground wire, but no neutral wire.

Use a voltage tester also known as a "wiggy" to determine whether you are dealing with a 110v or 220v powered line. It is important to note that the terms 110v and 220v are antiquated and have been replaced by 120v and 240v respectively.

Take the red probe and touch the tip directly to one of the two non-ground copper wires. Repeat the same process with the black probe, but make sure to connect it to the other non-grounded copper wire. The meter on the voltage tester will tell you if the current running through the wire is 120v or 240v.

Utilise powerful items such as an electric clothes dryer, air conditioner or central heating only with 240v circuits. The reason for this is that more amps and current can be drawn from 240v than from 120v.

Use only small items such as mixers, chargers, televisions and stereos for household plugs that only have a 120v current. For this reason, if shocked by 240v vs. 120v, particularly when the appliance is pulling power, it will hurt a lot more.


Make sure to use caution when working with live wires. Be sure to remove any rings or jewellery prior to working with electricity. If an accident were to occur, the metal from the jewellery could become flash-fried to your skin/bone requiring surgical removal.

Things You'll Need

  • Klien tools voltage tester
bibliography-icon icon for annotation tool Cite this Article

About the Author