How to Tell the Difference Between 110V and 220V

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Have you ever tried to plug a vacuum cleaner into a dryer receptacle or a dryer into a regular household outlet? Neither fits, and there's a good reason. A dryer runs on 220 voltage, whereas a conventional receptacle supplies power at 110 volts.


110V vs. 220V Power

You may see 220-volt service described as 230, 240 or 250 volts. They are all the same, just as 110-volt service can also be described as 115, 120 and 125 volts.

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Electricity comes into the home from the power line transformer in a pair of hot wires with an effective voltage of 240 volts between them. Each wire attaches to a bus bar in the main panel, and a return (neutral) bus sends a single wire back to the transformer. The nominal voltage between each hot bus and the neutral bus is 120 volts. As electricity courses through circuits in the house, the voltage fluctuates, which accounts for the different designations.


Most household devices, including lights and appliances, run on 110-volt power. They connect to the panel via a single hot wire (which connects to one hot bus), a neutral wire and a ground. Larger appliances, such as dryers, run more efficiently on 220-volt power. They connect to the panel via two hot wires (one for each bus bar), a neutral and a ground.

220 Voltage Calls for Double Pole Breakers

Because it's a switch, a circuit breaker must be installed in the hot leg of the circuit it controls. The easiest way to accomplish this is to snap it directly to the hot bus and connect it to the hot wire for the circuit it controls.


Each 110-volt circuit connects to a single bus bar and has only one hot wire, so only one circuit breaker is needed. By contrast, a 220-volt circuit connects to both bus bars, so two breakers are needed – one for each bus bar and each wire that connects to that bar. A 220-volt breaker is known as a double-pole breaker, and it consists of two 110-volt breakers bonded together.

The Difference Between a 110 and a 220 Outlet

Virtually all 110 volt outlets look the same. They have two vertical slots placed side by side, one of which may be larger than the other if the outlet is polarized. There may also be a third semicircular slot forming a triangle with the other two. It's for a ground pin.


There is no such commonality among 220-volt outlets. The pin configuration depends on the current rating of the breaker controlling the circuit. However, there are a number of key differences between a 110 outlet and a 220 outlet:


  • The 220 outlet is larger, and it's usually round and black or dark brown, not white.

  • It can have three slots or four. Four-slot outlets have a ground wire. One or more of the slots is set horizontally or at an angle.

  • There is only one outlet, unlike 110 outlets, which are almost always installed in pairs called duplexes.


What's Inside a 110 or 220 Outlet?

If you look at a 220V to 110V wiring diagram, you'll note that a 220V circuit has two hot wires. That means a 220V plug has to have an extra hot terminal, which is brass by convention. Also by convention, the hot wires are colored black and red. A 110V outlet (and plug) has only one hot terminal, and the hot wire is always black.


Another key difference between 110 and 220 circuits is the wire size. Because 220-volt circuits carry higher current, they require 10 gauge or larger wire, whereas the normal maximum wire size in a 110-volt circuit is 12 gauge. The terminal screws in 220V plugs and outlets are accordingly larger.



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