You can test a power cord with a basic digital multimeter in about five minutes. The process involves a visual inspection followed by continuity testing to confirm each wire inside the cord carries electricity from one end to the other. If any wire is broken internally or shorted to another, the cord needs to be replaced.
Start With a Visual Inspection
Before you reach for any tools, unplug the cord and look it over carefully. You’re checking for three things: frayed or exposed wires, cracked or brittle insulation, and burn marks or discoloration on the plug prongs or connector. Pay close attention to the spots where the cord meets the plug and where it enters the device connector, since these stress points are where internal wires most commonly break.
If you see exposed copper, melted plastic, or blackened prongs, stop testing and replace the cord. These are fire hazards, and no amount of electrical testing changes that. If the cord looks physically intact, move on to testing with a multimeter.
What You Need
A digital multimeter is the only tool required. Any basic model with a continuity mode will work. Continuity mode is usually marked with a small speaker or sound wave icon on the dial, and it’s often grouped with the resistance (Ω) setting. Some meters require you to press a separate button to activate the beeper after selecting that dial position.
Make sure the cord is unplugged from both the wall outlet and the device before any testing. You’re sending a tiny signal from the multimeter’s own battery through the cord. Plugging into a live outlet while testing could damage your meter or injure you.
How to Test for a Broken Wire
A continuity test checks whether electricity can flow through each conductor in the cord from one end to the other. Here’s the process:
- Set up the multimeter. Insert the black test lead into the COM jack and the red lead into the jack marked VΩ. Turn the dial to continuity mode.
- Verify the meter works. Touch the two lead tips together. You should hear a continuous beep, confirming the meter is functioning.
- Test the first conductor. Touch one lead to one of the flat prongs on the plug end. Touch the other lead to the corresponding pin or contact on the device connector end. If the wire is intact, the meter will beep continuously. A short, momentary beep doesn’t count as continuity.
- Test the second conductor. If the first prong didn’t produce a beep, try the other prong with the same connector pin. Once you find the matching pair that beeps, move on and repeat the process for the remaining prong and its corresponding pin on the other end.
A standard two-prong cord has two conductors to test. A three-prong cord has three: the two flat blade conductors plus the round ground pin. Test each one individually. If any conductor fails to produce a continuous beep, the wire is broken internally and the cord should be replaced.
How to Test for a Short Circuit
A short occurs when two conductors inside the cord are touching each other, which can trip breakers or damage equipment. After confirming each wire has continuity on its own, test for shorts by touching both multimeter leads to the two prongs on the plug end (don’t touch the device connector end at all). If the meter beeps, the conductors are connected to each other inside the cord, meaning it’s shorted. Replace the cord immediately and do not plug it into an outlet.
On a three-prong cord, test each combination of prongs: left to right, left to ground, and right to ground. None of these pairings should produce a beep.
Testing the Ground Pin
If you’re testing a three-prong cord, the round ground pin deserves extra attention. The ground wire is your safety backup. In a fault condition, it provides a path for stray current to flow safely to earth instead of through you.
Test ground continuity the same way you tested the other conductors: one lead on the round ground prong, the other on the ground contact at the device end of the cord. You want a continuous beep and, if you switch to resistance mode, a very low reading, ideally under a few ohms. A high or infinite resistance reading means the ground path is compromised, which makes the cord unsafe even if the other two wires test fine.
When Continuity Passes but the Cord Still Fails
A continuity test confirms a wire isn’t completely broken, but it won’t catch every problem. A wire with internal corrosion or partial damage can pass a continuity check while still dropping significant voltage under load. Visual inspections miss most of these cases because the corrosion is hidden inside connectors or under insulation.
If your cord passes both continuity and short-circuit tests but the device still malfunctions, you can check for excessive resistance. Switch your multimeter to the lowest ohms (Ω) range and test each conductor end to end. A healthy power cord should read very close to zero ohms, typically under 1 or 2 ohms for a standard-length household cord. If you’re seeing 5 ohms or more, internal wire damage is creating resistance that will reduce power delivery and generate heat.
A more advanced option is a voltage drop test, where you measure the voltage at the plug end versus the device end while the cord is carrying its normal load. This requires the cord to be plugged in and powering a device, so it’s best left to someone comfortable working around live circuits. For most people, the resistance check with the cord unplugged gives a good enough picture.
Insulation Testing for Older or High-Value Cords
Standard multimeters test what’s happening inside the wires. Insulation testing checks the material between the wires to make sure current isn’t leaking where it shouldn’t. This requires a specialized tool called a megohmmeter (sometimes called a “Megger”), which applies a higher voltage than a regular multimeter to stress-test the insulation.
The general rule used in electrical maintenance for decades: insulation resistance should be at least one megohm (one million ohms) for equipment rated up to 1,000 volts. Household power cords fall well within that range, so one megohm is the minimum acceptable reading. Anything lower suggests the insulation is degraded and current could leak between conductors or to the outside of the cord.
Most people testing a suspect laptop charger or appliance cord won’t need a megohmmeter. But if you’re evaluating older extension cords, cords stored in damp environments, or cords for critical equipment, an insulation resistance test adds a layer of confidence that a simple continuity check can’t provide.