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Measuring Current With Multimeter

1. Two Ways Of Measuring Current

Current is incredibly dangerous and can kill you. Touching a high current wire can be like getting struck by a lightning bolt. Use extreme caution when handling live wires or measuring current.

Recall that “A” stands for amps. Amps is the unit of current. Before taking any current readings, look at the “A” port on your multimeter. The number next to the “A” is the maximum current your multimeter can handle. Do not measure any current that will exceed this limit.

There are two ways to measure current.

• Using a clamp meter

• Using a digital meter

This chapter will teach you how to measure current with a clamp and digital meter. Let’s start by learning how to use a clamp meter.

2. How to measure current using a clamp meter?

A clamp meter is the simplest and safest way to measure current. A clamp meter does not require you to touch any wires. This significantly reduces chances for an injury. Let’s start by learning how to set your multimeter dial to measure current.

Recall that there are two types of current, AC and DC. Recall that in AC current, the direction of flow alternates direction. DC current only flows in one direction. The schematic diagram for the equipment will indicate if the system is AC or DC.

If you are measuring AC current, point the dial towards the “A” with a wave over the top. If you are measuring DC current, point the dial towards the “A” with a straight and dashed line on top. You may need to press the yellow function key to set the meter to AC or DC. See the meter to the right for an example.

Since you will be using the clamp to measure the current, you do not need multimeter leads. Remove any multimeter leads that you have plugged into your multimeter.

Press the button on the left hand side of the multimeter. This will open the clamp jaws. Move the multimeter so that one wire is inside the clamp - then release the button so that the jaws close. Do not touch the wire during this process. Only move the multimeter.

Once the wire is inside of your closed meter, position the wire in the center of the clamp. The wire should not be touching any surrounding edges of the clamp or the multimeter. Read the current and unit on the multimeter’s display. For example, 200mA.

Recall that a live wire refers to a wire with power running through it. When you are using a clamp meter, do not touch the wire you are measuring. Your hand should be on the bottom half of the meter. The farther your hand is from the live wire, the safer you are.

3. How to measure current using a digital multimeter?

Next, you will learn how to measure current with a digital multimeter. Measuring current with a digital multimeter can be very dangerous. Use extreme caution. Always treat wires as if they have power.

When measuring current, you should always start with the A port. Some multimeters will have a port for measuring small amounts of current. This port is labeled “mA”. Do not use the mA port until you have confirmed that the current is small. You risk injury by using the mA port on large amounts of current.

If you are measuring AC current, point dial towards the “A” with a wave over the top. If you are measuring DC current, point the dial towards the “A” with a straight and dashed line on top.

To measure current, you cannot just touch your probes to the circuit. You must connect your multimeter leads in series with the circuit. Recall that an in series circuit only has one path for the current to flow. Current moves from one component to the next.

To measure current you must connect your meter leads in series with the circuit. To do this, you will have to disconnect the circuit. This step can be extremely dangerous. If possible, use a clamp meter instead of a digital meter. A clamp meter does not require you to disconnect a circuit.

To connect your multimeter in series, turn off the power to the circuit. Once the power is off, continue to act as if the circuit has power. Confirm that the circuit is de-energized by measuring the voltage of the circuit. If there is no voltage then you can continue.

Disconnect the wire leading into the component you are measuring. There should be an open gap in the circuit now. Press one multimeter lead to the end of the disconnected wire. The other lead should be pressed into where the wire would connect into the component.

Turn the power back on once you have safely connected your multimeter in series. Do not touch any live wires or you can be fatally injured. Hold your probes as far from the metal tips as possible while maintaining control.

The current should be reading on your multimeter display. The units will be shown on the multimeter display as well. In the example to the right, your meter is reading 0.79A of AC current.

4. Conclusion

In this section, you learned how to measure the current across a component with a digital and clamp multimeter. In the next section, we will teach you how to measure resistance.

Question #1: Current can easily kill you if you are not careful.

1. True

2. False

True, current is incredibly deadly. Be very careful. Note the maximum current your meter can handle.

Question #2: A clamp multimeter can only measure the current of one wire at a time.

1. True

2. False

True. When you are measuring current, only place one wire in the multimeters clamp.

Question #3: You should hold the wire you are measuring the current of.

1. True

2. False

False, you should never touch a live wire with your hands.

Question #4: What port does your black lead plug into while measuring current?

1. A

2. mA

3. COM

Your black lead will always be plugged into the COM port when measuring current.

Question #5: You should use the “mA” port when measuring large amounts of current.

1. True

2. False

False, you should always use the “A” port when measuring current. Once you know the current, you can move to the “mA” port for better resolution.

Question #6: To measure current with a digital multimeter, you must connect your leads in:

1. Series

2. Parallel

3. Line

4. Rotary

When you are measuring current with a digital multimeter, you must disconnect the circuit and attach your leads in series.

Question #7: When disconnecting the circuit, you must:

1. Turn the power off

2. Wear all necessary safety gear

3. Confirm the circuit is de-energized

4. All of the above

Disconnecting the circuit can be extremely dangerous. You must turn the power off, wear all safety gear, and confirm the wire are de-energized.

Question #8: It is okay to touch a live wire with your hand.

1. True

2. False

False, you should never touch a live wire with your hand. Always turn off the power and confirm there is no power before handling a wire.

Question #9: Digital multimeters are safer than clamp multimeters when measuring current.

1. True

2. False

False, clamp multimeters are safer than digital multimeters. With a clamp multimeter, you do not need to disconnect the circuit.

Question #10: Once you turn the power off, it is safe to assume that the circuit does not have power.

1. True

2. False