What Happens When 120V Is Plugged Into 240V?

Different electronic products use different volt outlets for power transmission. 120V and 240V are the two types of outlet. The former is the standard for most US homes, and the latter is used only for kitchen and utility appliances. Having both outlets does not mean you can run any appliances anywhere. 

If you plug a 120V appliance into the 240V outlet, then your fuse may blow up, or your circuit breaker will pop. The appliance will likely get overloaded, and the circuit may fuse or catch fire resulting in electric shocks and other mishaps. You can only plug it safely by using a step-down transformer.

You must use appliances in the right outlet. Otherwise, they will not work well. This guide will explain the difference between the two voltages and the result of running the appliances in the outlet having the wrong voltage. 

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What is the difference between 120V and 240V?

As a beginner, it is important to understand the difference between 120V and 240V as these are the commonly used outlets, the former being the most common. 

Understanding the difference will let you know which appliances should be used in which outlets.

120V is the standard outlet to plug in every small household appliance, like the vacuum cleaner or phone charger.

A 240V outlet is used for larger appliances that need high-voltage outlets, like air compressors, ovens, etc. 

The outlets have 3 to 4 individual plugs of various sizes. 

It is safe to go with the 120V outlets for your home. 

Most of the daily household devices can get along with this voltage. 

But, in some places, 240V will be more beneficial for some appliances. 

When is 120V enough?

Almost all the everyday appliances are good to run in the 120V outlets. 

Appliances like microwaves, dishwashers, and refrigerators can smoothly run on 120V outlets. 

These outlets are present all over your house. 

You can identify it by the size and number of prongs. 

An outlet with 2 prongs is a 120V outlet. 

A 240V outlet will look larger than a 120V outlet and have 3 prongs with a Y shape. 

When do you need 240V outlets?

Some appliances in your house will require voltages of more than 120V for adequate and flexible functioning. 

Washing machines, dryers, ovens, and air compressors are common examples that run better on a 240V outlet. 

You can also run these appliances in a 120V outlet, but they work very efficiently. 

For example, you can run an oven in a 120V outlet, but it will produce heat less than the average level. 

But, on a 240V outlet, it will produce heat as it is supposed to produce. 

To install the 240V outlets, you need to know where exactly you will put these appliances. 

You will have to install these outlets in areas where you will permanently place these appliances. 

What happens if you plug in any appliance in the wrong outlet?

While you can run certain appliances at any voltages under 100V to 240V, some appliances will require a specific voltage for smooth operation. 

These appliances are called single input voltage appliances, like:

  • Motors
  • Heaters
  • Lights
  • Hair dryers
  • Kettle 

If you connect an appliance to the wrong outlet, the appliance will not run properly. 

For example, if you run a 110V appliance to a 220V outlet, the power will quadruple right after you switch it on. 

The appliance will start operating quickly due to the overvoltage it is receiving. 

It will get accompanied by a flash, smoke, fuse melt, and damage to the part that helps protect everything. 

Due to the overvoltage, many other components will get burnt. 

This burn can also injure some parts of the appliance and damage it. 

When you do the opposite thing, i.e., plugging in a 220V appliance to a 110V outlet, the power the appliance gets will be 1/4th of the original volt outlet. 

For example, if you plug a 220V lamp into a 110V outlet, it will produce below the average light. 

Besides, the motor will turn slow or stop working. 

Sometimes, the appliances will not work at all. 

Generally, the single input voltage devices will work only at specifically rated voltages. 

You can use a volt converter to run the appliances in a different rated outlet. 

The voltage converter will help to convert the voltage to acquire the required voltage and help in a smooth and safe operation. 

What happens if I run a 120V appliance to a 240V outlet?

Though both the voltages have more or less the same physical dimensions, the prongs are different. 

A 120V outlet will have 2 vertical prongs, and a 240V outlet will have 4 holes. 

A 120V appliance that is to be run in a 120V will not be able to run the voltage in a 240V outlet. 

For example, you cannot run a microwave with 120V on a 240V outlet. 

The appliance will start burning out very quickly in a 240V outlet. 

Due to the overvoltage, you will notice flames, flashes, and smokes. 

Due to these burns and flames, the appliance parts may get damaged. 

It can also melt the fuse and start a short circuit or fire. 

The problem occurs because the plug shapes are different in different countries. 

So, you must be careful and know the appliance’s voltage and the outlet before plugging it in. 

Use the particular outlet if your appliance is specifically rated for a lower voltage, around 110 to 120V. 

Can I use converters to run a 120V appliance in a 240V outlet?

Voltage Converter, GEARGO 230W Power Converter Step Down 220V to 110V Universal Travel Adapter for Hair Straightener, Curling Iron with 4-Port USB Charging UK/AU/EU/IT/US Worldwide Plug Adapter White

You will need a power converter to run a 120V appliance in a 240V outlet. 

These converters will allow you to run appliances between 110V and 120V in 220 and 240V outlets.

However, you must be careful while running the appliance in these outlets. 

Despite using the converters, there could be chances of the appliances getting damaged. 

You also must ensure that the transformers you use have greater wattage than the appliance you plan to plug in.

Normal electrical wiring will have three wires – a hot, neutral, and ground wire. 

But a 220V or 240V wiring system will have four wires – two hot wires, one neutral, and one ground. 

Suppose you do not use any converters or transformers. 

In that case, the appliance will fail to work due to overvoltage, causing sparks and electric fire. 

It can ignite any flammable material near the appliance. 

Can I convert 120V to 240V?

To convert your electrical system from 120V to 240V, you must connect the two power lines and a ground wire. 

The voltage between the two power lines has to be the same. 

You must disconnect the 120V outlet from the panel by loosening the screws holding the terminals. 

Find the neutral terminal for the white wire and unplug it from the panel. 

Connect the wires to the new circuit and attach the new plastic caps to the splices. 

Make sure that the breaker is a 2-pole breaker, as these are specifically designed for both the legs of 120V and 240V. 

Use breaker panels made by Sta-blok, FPE, or Schneider. 

You might also have to change the wires if the outlet wire does not support 240V. 

That is a different project, including opening the walls to change the wire. 

Can an outlet work for both 120V and 240V?

You need an adapter if you wish to use an electrical outlet that supports and works for both 120 and 240 voltages. 

It lets you connect the 120V outlet to a 240V outlet, but you must ensure that the adapter can work for both voltages. 

If you do not have any idea, test the voltage with a neon voltage tester. 

Remove the cover and find the terminals. 

Disconnect the wires connected to the terminals with a screwdriver. 

Connect the ground wire with the green terminal screws on the outlet to test the current.

Another option is a ballast ply converter. 

This converter allows you to convert a 120V ballast plug into a 220 or 240V-style plug. 

This converter is used for customers who own 120V ballasts but want to connect them with a 240V lighting controller. 

The voltages get similar, but the wire gauge will be different. 

What about 110V outlets?

We have known till now that using a 120V appliance in a 240V outlet will result in fire, flames, flashes, and fire. 

If you have an appliance rated at 110V or 120V, you need to use the same outlet, i.e., 120V, for both. 

But is it possible to use 120V appliances in a 110V outlet?

There is no issue in plugging a 120V appliance into a 110V outlet. 

It is because there is very little difference in both the voltages. 

Besides, modern-day electrical devices can withstand 5 to 10-volt differences in the current line. 

Most US houses use 120V appliances and outlets, except for some larger appliances. 

So, it usually means that you can run the 120V appliances in outlets ranging between 110V and 120V as long as you do not go beyond 120V. 

Can I use a 120V bulb in a 110V socket?

There is no problem in using a 120V bulb in a 110V socket. 

In the US, the standard voltage is around 120V to 125V. 

If the outlet is 110V, the voltage supply won’t be less than the 120V socket due to the voltage fluctuation. 

So, 120V outlets can give low voltages, around 115 volts, and a 110V outlet can also provide up to 115 volts. 

There is not much difference between the 110V and 120v outlets. 

That is why using a 120V appliance in a 110V is completely fine. 

Will the 120V appliance run slow in the 110V outlet?

Generally, a high-voltage appliance can run slowly or stop running in a low-voltage outlet. 

But, in this case, the appliances will not run slowly because there is not much difference between 110V and 120V. 

Besides, the electric power does not completely depend on the voltage level. 

The power is the result of the multiplication of voltage and electric current. 

As long as the power output and electrical outlet are the same, the 120V device will run at a proper speed on a 110V outlet. 

Is 110V very low for 120V appliances?

It may seem low, but the running speed of the 120V appliances in the 110V outlet will not let you understand that. 

The appliances will run at the proper speed in the outlet. 

Generally, a 110V outlet is 8% low for 120V appliances. 

Still, you will not find much difference in the speed of the appliance function. 

It is because the AC or alternating current in the US never provides current at a perfectly stabilized 120V. 

It keeps fluctuating between 110V and 125V.

Also read: Can You Use US Electrical Appliances In The UK? (Problems+Solutions)

Final thoughts

You can use some appliances in any outlets ranging from 100V to 240V; some appliances specifically require a dedicated outlet. 

A 120V appliance will work only in an outlet specifically rated at 120V. 

The same goes for 240V appliances. 

Plugging a 120V appliance into a 240V outlet will make the appliance run faster than normal due to overvoltage. 

That will lead to flames, flashes, and smoke. 

The fuse will melt and start a fire or short circuit. 

The parts that are supposed to protect the outlet will also get damaged. 

Due to the overvoltage and fire, the appliance parts can also get damaged. 

If you use a high-voltage appliance in a low-voltage outlet, the product will either work very slowly or won’t work at all. 

So, it is always better to use the right outlet for every appliance. 

If you want to use a 120V appliance in a 240V outlet, you can use a converter to change the voltage. 

You can also use a plug adapter to connect 120V and 240V, but make sure the adapter works for both voltages. 


Can I plug 120V air conditioners into a 110V outlet?

You can plug the 120V AC into a 110V outlet, but it will not work. 

The outlet is designed for the 115V AC power that the air conditioning units use. 

How much will it cost to install 240V?

Installing a 240V outlet will need around $300, and conversion will require around $300 to $800.

How much will it cost to install a 120V?

Installing a 120V outlet will cost around $145 to $200.  

Reference: University of FloridaElectrical systems differIEC World Plugs, ResearchGate, Electrical Injuries.

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Arthur Smith

Howdy! I am Arthur Smith, an electrical engineer who is extremely passionate about electronics. I have lived in different parts of the US and currently reside in Wisconsin. I am one of those rare children who knew what he wanted to study and do in life right from the start. I was a curious child who wanted to know how switches work and how the AC works, and I would always observe my dad whenever he would handle the wires and fix things around the house. I currently work as an electrical engineer at a reputed company and write for this blog. And I read loads of books or play video games in my free time.

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