How to measure leakage current with a digital multimeter?

How to measure leakage current with a digital multimeter

What is leakage current? Leakage current in an electrical circuit is one type of problem with the current that flows from the circuit into the ‘ground’. To understand ground, you think of a normal grounded outlet in the US.  A grounded outlet is the one with three holes instead of two. The slightly bigger hole that’s placed below the two vertical slots is the ground. This allows the electricity to safely return from the circuit, in case of a ‘short circuit’. Without the ground, a short circuit would be dangerous for the circuit, for the appliance you’re using, or for you.

Normally, the electrical current flows from the positive side (the right hole) to the negative side on the left, with the ground in place to safely ‘return’ the electricity. When we put the example of the outlets aside, this is still how any electrical circuit works. In a normal circuit, there is hardly any leakage from the circuit into the ground.

The problem of leakage current then is the leakage of current from the normal circuit that flows from positive to negative into the grounded part of the circuit. This means a loss of efficiency at best, but leakage current can cause a lot of other problems, too.

Why is leakage current a problem?

Although a small amount of leakage is always going to occur, a noticeable change might be dangerous or even fatal. An improperly grounded device can leak into a person, which is something we always want to avoid. When working with electricity, we always want to keep it away from ourselves and contained to the circuit.

On a less serious level, a common problem with leakage current is that it unnecessarily trips some GFCI outlets, or simply causes a rise in voltage, which can cause problems in the appliances or circuits you’re working with. Sometimes, this rise in voltage can ‘blow up’ your device. In other cases, leakage current can indicate defective insulation, which is a problem that should be repaired as soon as possible. Again, we want the electricity to stay inside the circuit, and inside the insulation, too.

Measuring leakage as a current

A lot of measurements you do with your multimeter are voltage measurements. Voltage is the total capacity of a circuit or electrical component. With leakage current, you want to measure the current. If voltage can be compared with the measurement of the width of a classic plumbing pipe, indicating how much water can flow through it at any time, the current would be a measurement of how much water actually flows through. In an electrical circuit, the current is a measurement of how much electricity is flowing through the circuit.

To measure the current flow, you’ll have to intercept the circuit. This way, you technically build a detour for the current flow, at which you measure the current. This also means you’ll have to break the circuit temporarily.

How to measure leakage current with multimeter

A lot of digital multimeters have a function that will allow you to measure current. As you can imagine, this makes it a lot easier to actually perform the test. Before you set out to measure leakage current, double-check your manual to see where to insert the probes. Remember that not every test requires your leads to be in the same position.

Once you’ve set your multimeter to the current setting and put your leads in the right place. If you have a manual ranging digital multimeter, select the correct range. If you’re not sure about the range, it’s best to start high and work your way down until you find yourself in the right range. This prevents the meter from being overloaded.

Now, put each of the leads at one point on the circuit, so one end is down the line from the other. The best way to do this is by using clean and completely closed alligator clamps. Once the clamps are in place, this creates the interception we talked about before. After a little while, you can read the current on your screen.

How to measure leakage current with a leakage current clamp meter

If you suspect to encounter leakage current regularly, you might want to invest in a leakage current clamp meter. As the name suggests, this piece of equipment is perfect for measuring leakage current. Many digital multimeters have a leakage current clamp meter available as an accessory, but you could also find them as a stand-alone product.

To use the leakage current clamp meter, place the jaws of a clamp meter around the conductor. This automatically starts the reading process, and eliminates the intercepting of the circuit as we saw in measuring leakage current with a digital multimeter.

How to measure leakage current in the car

One common place you may find leakage current is in your car. Because it is so common, we want to discuss it separately, although the basics will be no different than what we’ve discussed so far. To measure leakage current in the car, make sure that your car is turned off and the key is not in the ignition.

To measure leakage current in the car, switch your multimeter to measure DC current, put the leads in the right portals, and put one lead on the negative terminal of the car battery and the other lead on different wires. When you find a big difference in the readings, you found a leakage current, which should be fixed.


Now you know how to measure leakage current with a digital multimeter. Make sure to read the manual for your multimeter and go through a ‘dry run’ before you try to measure leakage current. If you’re still unsure how to do it, it’s best to consult a professional. Always make sure you follow all the safety instructions and double check whether the circuit is turned off.

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