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Troubleshooting a Low Voltage condition at the device. (Contactor, Coil, Relay, Brake etc.)

Example low voltage electrical condition in circuit
Problem- Voltage from A1 to A2 of contactor coil =15vdc, should be 24vdc (assume 24vdc solenoid coil is the load)

Check at power supply from +24 to 0vdc is it 24VAC?


Go to next step (Power supply good)



  1. Power down

  2. Remove all wires connected to +24, 0vdc on power supply

  3. Power up

  4. Recheck power at power supply. If 24vdc, then power supply is most likely OK unless the power supply has weekend over time. Otherwise there is an excessive amount of current drawing down power supply or something wrong with power coming into the primary side.

  5. Check out diagnosing power supply problems.

Problem could be a loose connection or bad contact in a device/relay/ or contactor.


Follow through the series circuit and tighten all wire terminals. Don't forget to check A2 (0VAC) wire terminals too.

If the CNC machine tool is relatively new also check for terminals crimped on insulation of wire

If still have problem. Check entire circuit with meter and test each point on each side of every contact, circuit board, relay or any other device in the series circuit. Looking for the voltage drop across the device and then troubleshooting that device. See points in example circuit that were checked.

Contactor relay troubleshooting - see electrical shorts for other possible solutions