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Wiring and Circuits (2019)
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Wiring and Circuits (2019)

Connectors

Mini Project Testing Wires with a Multimeter

A multimeter is a handheld device that can measure ("meter") several different electrical properties ("multi"), depending on what mode it is set to.

One of its uses is to test whether there is a complete electrical connection between two points. This is helpful for checking whether a wire has been correctly constructed.

Testing Wires with a Multimeter: Required items and tools

To begin testing wires, you will need the following:

  • Digital Multimeter Digital Multimeter
Checking Continuity

A multimeter can be used to test for an unbroken electrical connection between two points. Something with no breaks is called "continuous", so this process is called "continuity" testing.

Selecting Continuity Testing Function

The continuity testing function of the multimeter tests for electrical continuity between two points that you touch the multimeter's leads to.

Tip: If there is a continuous connection, the multimeter will make a beep sound, so the icon for this mode usually looks like a "sound waves" symbol.

  • Some multimeters do not include this feature. If yours does not, follow the steps below but use the lowest-value Resistance test feature (Ω) on your multimeter instead, and instead of a beep, look for a resistance value of zero or near zero to be shown on the screen.
Safety Notice

The continuity tester does not work on circuits that have power running through them. Disconnect power from the portion of the circuit you are testing and test the parts individually. The multimeter may be damaged if you attempt to use this feature on a powered circuit.

Step 1: Plug black lead into multimeter

Plug the black lead of the multimeter into the COM terminal.

Step 2: Plug red lead into multimeter

Plug the red lead of the multimeter into the terminal with one of the following icons next to it:

  • Continuity Symbol Continuity Symbol
  • Ohms Symbol Resistance (Ohms) Symbol
  • Voltage (Volts) Symbol Voltage (Volts) Symbol
  • Diodes Symbol Diodes Symbol

Tip: The continuity test feature is electrically similar to several other multimeter functions, so it usually shares a plug and a spot on the dial with one of them. Different multimeters have it share with different modes.

Step 3: Turn dial to Continuity Testing setting

Turn the dial to the connectivity testing setting.

Some multimeters, like the orange one shown, have multiple functions on a dial setting. You may need to press the FUNC or function button to switch the multimeter to the connectivity testing setting. Look for the connectivity symbol on the screen of the multimeter.

Step 4: Touch leads together

Touch the metal parts of the multimeter leads together. The multimeter should make a sound while they are in contact (because the two leads are electrically connected to each other).

  • If no sound is played, check your connections and try again.
Step 5: Touch the leads to the wire

Touch the two leads to the ends of the wire you want to test. If you hear a sound, it means that there is a continuous electrical path between those two points.

  • This means there is no connection between the two points. Try to narrow down where the problem is by testing shorter portions of the wire. For instance, try touching the leads directly to the conductor in the wire -- if that part passes, then the problem must involve one of the connectors.
  • This either means you are trying to test for continuity across a component like an LED that cannot be tested using this mode (use Diode test mode instead), or it means the connection is loose.
  • The connector may be not be tightly crimped onto the wire conductor. Try tightening it.
  • You may also have damaged the conductor itself while attaching the connector -- for instance, you might have accidentally cut into the conductor while removing the wire insulation. This generally cannot be repaired, and you should remake that portion of the wire.
Step 6: Turn dial to Off

Turn the multimeter dial back to the OFF position when you are done.

Check Your Understanding

Which of these terminals should the BLACK lead of the multimeter be plugged into for a continuity test?
Hover over parts of the image and click to select
  • 200mA to 10A current terminal
  • COM terminal
  • V/?/Hz/uA/mA/°C terminal
Which terminal should the RED lead be plugged into for this multimeter?
Hover over parts of the image and click to select
  • 200mA to 10A current terminal
  • COM terminal
  • V/?/Hz/uA/mA/°C terminal
Which terminal should the RED lead be plugged into for this multimeter?
Hover over parts of the image and click to select
  • 200mA to 10A current terminal
  • The selected terminal only receives the red lead, to measure capacitance, temperature, hFE and 0.001mA to 200mA current.
  • Return terminal for all measurements
  • Voltage, resistance, frequency, diode, and continuity test terminal

Testing Alligator Clip Connection

Testing Alligator Clip Connection with Multimeter

Make sure there is solid electrical continuity across your entire wire, from the tip of the alligator clip all the way to the conductor on the other side.

  • Construct a new wire. You will not be able to reuse the alligator head connector (the crimped loop part cannot be un-bent), so instead cut the connector off and try again with the remaining wire.
Which of the following are appropriate ways to test whether an alligator head is correctly attached?
  • Pull firmly on the ends of the wire to see if anything comes off
  • Use a multimeter to test for continuity from one end to the other
  • Attach a battery and see if it heats up
  • Use a multimeter to test that there is NOT continuity along the insulated part of the wire
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