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How to Make a 240-Volt Extension Cord [8-Step Method]

Occasionally, the cord that comes with a power tool may be short for your location. To avoid this circumstance, you must take whatever steps you can to fix it.

How to make a 240-volt extension cord?

Choose a cord and calculate its power intake. Do some trimming after sliding the plugs into the cord. After that, expose the wires inside and get rid of the insulation. Insert the bare wires into the terminals carefully. Tighten each terminal screw and then you’re good to go.

Do you want more in-depth details? I’ve also got you covered! Come along and learn all you need to know!

8 Steps for Custom Length 240-Volt Extension Cord

Making a custom 240-volt extension cord is neither too easy nor too tough. And don’t confuse making 240V with 208V as they are very different in application. You need to make sure to have the right extension cord of correct length and power rating. Making your cord means you can get a cord that fits your needs. 

But before that, you will need a few tools.

Things You’ll Need
Here get the list of tools those will require:

  • 240-volt cord according to your needs
  • Male and female plugs
  • Electrician’s screwdriver
  • A knife

If you’re done collecting these items, then move on to the procedure. Here’s how you can make your extension cord-

Step 1: Select a Cord

Choose a cord that fits your requirements. Electrical cord must be able to be used indoors or outside.

For instance, in a snowy winter, a 240-volt generator is placed 30 feet away from the building to start a six-kilowatt heater. It’ll require a 240-volt outdoor-rated cable of 30 feet. Also, look for cables that have wire gauges large enough to handle the heater’s demands.

Begin by measuring the length of your cord carefully. Determine how much current the cord will need to handle. And establish what type of connections will be necessary at either end.

Step 2: Determine Appliance’s Power

Calculate how much power your appliances will need from the generator. An information plate for each appliance should show how much load it can take in kilowatts.

Divide the load by the voltage, in watts. For example, for 240 volts and a 12-kilowatt load, the current required is 50 amps.

Step 3: Plug in Extension Cords

Slide the new male and female plugs onto the cord. Ensure at least 5-6 inches of the cord through the housings of the new plugs. You’ll need enough cable between the plugs to work on the inner wires safely.

You can plug 2 extension cords in one outlet but with a risk of overloading.

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This product has good recommendations and is also reasonable in price.

Step 4: Trim-off Any Excess

Place each plug base in a way that the cord ends are even with the terminals. Take note of where the cable grip is. Then, with a knife, cut off the outer insulation from the cord just beyond the grip

Remove 2 inches of the outer insulating sleeve from each plug without breaking the wire insulation. Cut each wire accordingly to access the plug connections.

Step 5: Strengthen the Wire Ends

Expose the wires inside but leave the insulation where the cable grip will hold the cord. Trim the wire ends to prevent tugging or bunching when they reach the connections.

Get rid of the insulation. To strengthen the ends, twist the open wire filaments together.

Step 6: Wire Insertion into the Terminals

Insert the bare wires into the terminals with care. The grounding wire should be connected to the green terminal.

Connect the hot (black) and neutral (white) wires to the brass and silver terminals respectively.

The bare/ green-covered grounding wire must also be linked to the GND terminal.

Step 7: Check Terminal Screws

Tighten each terminal screw securely but not too tightly, then trim any extra wire.

Double-check that the wires are connected properly to the right terminals. Then attach the cable clamp to the remaining insulating cover.

Do inspect the wires visually to ensure they are not overtightened or trapped. Each plug should have its top housing replaced. Keep the cables tangle-free, just as you would your phone cords tangle free.

Step 8: Cross Check with Multimeter 

Before using your cord, check it with a multimeter to make sure there’s enough current. Put one of the probes from your multimeter into one of the plugs’ hot wires. But make sure to do this again between the neutral prongs and then the grounding prongs. 

In this case, all three tests show that the wires are connected correctly. The extension cord is now ready to be used!

Some Important Tips

Heavy-duty appliances require 240-volt outlets to be powered. When a big appliance is plugged into a 240-volt outlet, it runs more efficiently.

Consider these extension cord safety guidelines for you and your family.

Also, do watch out for these do’s and don’ts to make your journey smooth!


  • Acknowledge the amount of current drawn by your extension.
  • Circuit breakers should be sized appropriately for the extension.
  • The extension wire gauge should be selected according to the desired length and current draw. 
  • Maintain a short extension cable with the biggest gauge feasible.
  • Unroll extension cables to avoid a buildup of heat.


  • As a portable extension cable, use Romex or another strong wire.
  • Coil or uncoil solid wire repeatedly as it will degrade it.
  • Use a cable with a lower amperage rating than your extension or circuit. 
  • Keep extension cables coiled when in use.
  • Utilize any wire that lacks a ground plug.
  • Run multiple high-current tools concurrently on a cable or circuit.
  • Use a long extension cable if a shorter one is available.
  • Use permanent outdoor extension cords as it creates hazardous complications.

Always remember to test extension cables before using and repairing or replacing broken parts instantly.


Question: What is the best material for making extension cords?  

Answer: Firstly, you’ll need an SJ-cord that is 10/3.  You’ll also require screwdrivers, female and male cord plug caps, wire strippers, voltage tester, and wire strippers. 

Question: Can you run 240 volts through a 110-volt extension wire?

Answer: The 240v cable’s rating is the same as the 120v cable’s. Check the BS number to get an idea of how well insulated it is. The current rating is the same as 120v if the CSA is less than 2.5mm.

Question: Can you make an extension cord?

Answer: Your extension cord is usually three feet shorter than it should be. You can make it as long as you want. Remember to reduce the appliance’s power correspondingly.

Final Words

That’s all from my end. I hope you’re now clear on how to make a 240-volt extension cord.

Follow safety instructions as you’re dealing with electrical wiring. It’s better not to deal with any lethal consequences. Contact a professional if necessary. 

That’s it for today. Best of luck!