If the motor of the illustrated circuit...

Question 1 / 2066636eed28f7522a1c51d7e9

Question 1 of 2066636eed28f7522a1c51d7e9

If the motor of the illustrated circuit fails to start and gives a loud hum when the start button is pushed, what is most likely the problem? Illustration EL-0007

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Question 1 of 20

66636eed28f7522a1c51d7e9

If the motor of the illustrated circuit fails to start and gives a loud hum when the start button is pushed, what is most likely the problem? Illustration EL-0007

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🔍 Key Concepts

• Follow the power flow in the control circuit to see if the main contactor coil 'M' can still energize when the symptom occurs. • Understand what a three‑phase motor sounds/does when it is single‑phasing (one line open but the others energized). • Note where the overload (OL) heaters and the OL relay contact are located in relation to the motor and the M coil.

💭 Think About

• If the motor gives a loud hum, is it completely de‑energized, or is it getting some power but not enough torque to turn? What does that tell you about the state of the M coil and DS? • Look at which component, if open, would cut off ALL power to the motor versus only ONE phase to the motor. Which of the choices would still allow the control circuit to operate and pull in the contactor? • Compare the function of the OL heater element in the power legs to the OL auxiliary contact in the control leg. Which one being open would stop the coil from pulling in, and which one would mainly affect current to the motor windings?

✅ Before You Answer

• Verify whether the M coil is energized in this situation (does the circuit allow it to pick up when you press START?). • Check if an open DS or open OL relay contact would allow any voltage to reach the motor windings at all. • Identify which device, when open, would remove only one phase to the motor while leaving the control circuit and contactor operation normal.

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Question 1 of 20

If the motor of the illustrated circuit fails to start and gives a loud hum when the start button is pushed, what is most likely the problem? Illustration EL-0007

an open overload "OL" relay contact

an open overload "OL" heater

an open main contactor "M" coil

the disconnect switch "DS" is open

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Question 1 / 2066636eed28f7522a1c51d7e9

Question 1 of 2066636eed28f7522a1c51d7e9

If the motor of the illustrated circuit fails to start and gives a loud hum when the start button is pushed, what is most likely the problem? Illustration EL-0007

Back

Question 1 of 20

66636eed28f7522a1c51d7e9

If the motor of the illustrated circuit fails to start and gives a loud hum when the start button is pushed, what is most likely the problem? Illustration EL-0007

No comments yet

Be the first to share your thoughts!

If the question has a related picture, it will appear here.

🔍 Key Concepts

💭 Think About

✅ Before You Answer

👋 Hi! I'm Genie, your AI study assistant. How can I help you with this question?

Quick actions

— No credit card needed