How To Test An Extension Cord With A Multimeter

Have you ever plugged in an extension cord and found it doesn’t work? Annoying, right? Before you toss it out, let’s see if we can save you some cash and frustration by testing it with a multimeter.

This trusty tool can quickly tell you if the cord is the problem or if you need to look elsewhere. Let’s dive in!

How To Test An Extension Cord With A Multimeter

What You’ll Need

• A multimeter (preferably one that can test continuity)
• The extension cord you want to test
• A flat, stable surface to work on

Step 1: Set Up Your Multimeter

First, make sure your multimeter is set to the right mode. For testing an extension cord, you’ll want to use the continuity setting, which is usually represented by a symbol that looks like a sound wave or a diode symbol.

If your multimeter doesn’t have a specific continuity mode, the resistance (Ω) setting will also work, though continuity is preferable as it gives an audible beep if everything works fine.

Step 2: Test the Multimeter

Before testing the extension cord, it’s a good idea to test the multimeter. Touch the two probes together.

If you hear a beep or see a reading close to zero on the resistance setting, you’re good to go. If not, check your multimeter’s batteries or settings.

Step 3: Check the Extension Cord for Visual Damage

Before you start poking around with your multimeter, do a quick visual inspection of the extension cord. Look for signs of wear and tear, like cuts, frays, or bent prongs. If the cord looks damaged, it might be safer to replace it rather than try to repair it.

Step 4: Test the Plug End

Now, let’s get into the testing. Insert one multimeter probe into one of the slots on the plug end of the extension cord. With the other probe, touch the corresponding prong on the other end of the cord (where you plug in your devices).

• Continuity Test: If your multimeter is set to continuity mode and the cord is in good shape, you’ll hear a beep.
• Resistance Test: If you’re using the resistance setting, you should see a reading close to zero. A high reading means there’s a problem.

Repeat this process for each slot and prong combination. You should test all possible paths: hot, neutral, and ground.

Step 5: Test the Socket End

Now, let’s move on to the socket end of the cord. This time, insert one probe into one of the sockets where you’d normally plug in a device and touch the other probe to the corresponding prong on the plug end.

Like before, if everything works properly, you should hear a beep (or see a low resistance reading).

Repeat this for each socket and prong.

Step 6: Interpret the Results

• Beep or Low Resistance: Your extension cord is in good working condition.
• No Beep or High Resistance: This indicates a break or fault in the wiring, meaning your extension cord is no longer safe to use. It’s time to replace it.

Step 7: Final Check

If your extension cord has a switch, check it as well. With the cord plugged into an outlet, flip the switch on and off while testing for continuity at the socket end. A faulty switch could be the culprit if the rest of the cord tests fine.

Can You Repair a Faulty Extension Cord if It Fails the Multimeter Test?

While it’s tempting to try and fix a faulty extension cord—especially if it’s heavy-duty or expensive—it’s generally not recommended unless you’re experienced with electrical repairs. Here’s why:

1. Safety Risks: Extension cords are designed to carry a specific electrical load safely. If the cord is damaged and not repaired correctly, it can become a fire hazard or cause electrical shocks.
2. Complexity: Most extension cords have molded plugs and sockets, meaning they aren’t meant to be removed and reassembled. If the fault is in one of these areas, you’d need to cut and rewire the cord, which can compromise its integrity.
3. Cost vs. Benefit: In many cases, the cost of buying a new extension cord is low compared to the potential risks and effort involved in repairing one.

However, if you have experience with electrical work and the issue is simple—like a loose connection at the plug or socket—you might be able to fix it. Just make sure to use proper electrical tape or heat shrink tubing to insulate any exposed wires, and always test the cord with a multimeter after repairs to ensure it’s safe to use.

Can a faulty extension cord still pass a continuity test?

Surprisingly, yes! A faulty extension cord can sometimes pass a continuity test, especially if the issue is intermittent. For example, if there’s a loose connection inside the cord or the plug, the multimeter might show continuity when the wires are making contact but could fail when they shift or move.

This is why it’s important to rely on the continuity test and visually inspect the cord for any signs of damage and consider whether it has been working inconsistently. If you’ve had issues with the cord before, even if it passes the test, it might be safer to replace it to avoid potential hazards.

Conclusion

Testing an extension cord with a multimeter is a simple yet effective way to ensure it is in good working order. It only takes a few minutes and can save you from potential electrical hazards.

Plus, it’s a great way to make sure you’re not tossing out a perfectly good cord.

Frequently Asked Questions

• ABOUT AUTHOR

Author

Alex Klein is an electrical engineer with more than 15 years of expertise. He is the host of the Electro University YouTube channel, which has thousands of subscribers.