Electrician Red Seal · Question
A single-phase 2 HP, 120 V AC motor with a centrifugal switch fails to start. When you manually spin the shaft, the motor runs as expected, but without reaching full speed or power. What is the most probable cause of this failure?
If the motor starts by hand but fails to reach full power or speed, it indicates the start winding is not being used to provide the initial torque, but the run
Start free practice for Electrician Red Seal
150 questions · no signup required · 40 free questions per day
Question: A single-phase 2 HP, 120 V AC motor with a centrifugal switch fails to start. When you manually spin the shaft, the motor runs as expected, but without reaching full speed or power. What is the most probable cause of this failure?
Answer options:
- A faulty starting capacitor.
- A shorted running winding. ✅ A defective centrifugal switch that is not engaging the start winding.
- An open circuit in the main (run) winding.
Correct answer: A defective centrifugal switch that is not engaging the start winding.
Explanation: If the motor starts by hand but fails to reach full power or speed, it indicates the start winding is not being used to provide the initial torque, but the run winding is operational. A defective centrifugal switch that 'never closes' would prevent the start winding from being engaged, leading to this symptom. A faulty starting capacitor would prevent the motor from starting at all unless manually spun, but the motor would still attempt to run normally if the run winding is good. An open run winding would prevent any operation, and a shorted run winding would likely cause immediate tripping or overheating.
Start free practice for Electrician Red Seal
150 questions · no signup required · 40 free questions per day
More about Electrician Red Seal
Related Questions
- A residential garage is to be wired with a 15 A, 120 V duplex receptacle. According to the Canadian Electrical
- During a renovation of a commercial kitchen, an electrician needs to replace an old single-phase, 240 V, 5 kW
- A commercial kitchen is being renovated, and several new 4 kW, 208 V, single-phase electric ovens are being in
- What is the minimum working space depth required in front of an electrical panel rated 200 A, 120/240 V, locat
- A Red Seal electrician is setting up temporary power for a construction site. The main temporary service is a
- A new industrial facility requires a 600 V, three-phase, 150 A feeder to supply a motor control centre. The co
More for Electrician Red Seal candidates
Practice tests
Question explanations
- A residential garage is to be wired with a 15 A, 120 V duplex receptacle. According to the Canadian Electrical
- During a renovation of a commercial kitchen, an electrician needs to replace an old single-phase, 240 V, 5 kW
- A commercial kitchen is being renovated, and several new 4 kW, 208 V, single-phase electric ovens are being in
- What is the minimum working space depth required in front of an electrical panel rated 200 A, 120/240 V, locat
Ready to practice?
Free, no signup required. Build a wrong-question list as you go.
Start Free Electrician Red Seal Practice →Related courses
Other Canadian certifications candidates often prepare for alongside this one.