With the motor running at full load, voltmeter leads placed on L1 and T1 show 0 volts. What does this indicate?

With the motor running at full load, voltmeter leads placed on L1 and T1 show 0 volts. What does this indicate?

• A. Open circuit
• B. Shorted coil
• C. Good, clean contacts
• D. Ground fault

Answer: (C)

When the motor is running, the contactor should have its contacts closed, creating a direct, low-resistance path from the supply line to the motor terminal. Measuring the voltage between L1 and T1 and reading essentially zero volts means there is no potential difference across that path. That happens because L1 and T1 are effectively the same node through the closed contact, so the current flows with negligible drop. That is a sign the contacts are making a good, clean connection. If the contacts were dirty or loose, you’d expect a small voltage drop under load, or the motor might run with symptoms of high resistance. This reading doesn’t indicate an open circuit (the motor wouldn’t run) or a fault like a ground fault or a shorted coil, which would present differently. So zero volts here confirms the contacts are closed and conducting well.

When the motor is running, the contactor should have its contacts closed, creating a direct, low-resistance path from the supply line to the motor terminal. Measuring the voltage between L1 and T1 and reading essentially zero volts means there is no potential difference across that path. That happens because L1 and T1 are effectively the same node through the closed contact, so the current flows with negligible drop. That is a sign the contacts are making a good, clean connection.

If the contacts were dirty or loose, you’d expect a small voltage drop under load, or the motor might run with symptoms of high resistance. This reading doesn’t indicate an open circuit (the motor wouldn’t run) or a fault like a ground fault or a shorted coil, which would present differently. So zero volts here confirms the contacts are closed and conducting well.