CME Troubleshooting & Maintenance Techniques 2

Question 1

A motor repeatedly trips its overload relay shortly after reset. The motor is running at rated load. What is the MOST likely cause?

Accepted Answer

Undersized supply conductors causing voltage drop

Answer

Undersized supply conductors cause voltage drop, which increases motor current draw and causes repeated overload trips under rated load conditions.

Question 2

When using a clamp-on ammeter to troubleshoot a single-phase 240V circuit, you clamp around both conductors together and read zero amps. What does this indicate?

Accepted Answer

The circuit is operating normally with balanced current

Answer

Clamping around both conductors of a single-phase circuit cancels the magnetic fields, producing a zero reading when currents are equal and opposite — indicating normal balanced operation.

Question 3

A fluorescent lighting circuit has one lamp flickering while adjacent lamps on the same circuit are steady. What should be checked FIRST?

Accepted Answer

The lamp, ballast, and lamp holders on the flickering fixture

Answer

A single flickering lamp while others are steady points to a localized fault — the lamp itself, its ballast, or the lamp holders — rather than a circuit-wide issue.

Question 4

During megohmmeter testing of a motor winding, what minimum insulation resistance reading (in megohms) is generally considered acceptable using the 1-minute test method per IEEE 43?

Accepted Answer

0.1 MΩ per kV of rated voltage plus 1 MΩ

Answer

IEEE 43 recommends a minimum insulation resistance of 1 MΩ per kV of rated voltage plus 1 MΩ as an acceptable threshold for rotating equipment.

Question 5

A three-phase 480V motor is humming loudly and not starting. A voltmeter check shows 480V across two phases but zero volts on the third. What is the likely problem?

Accepted Answer

One phase of the supply is open (single-phasing)

Answer

Zero volts on one phase while the other two phases read correctly indicates an open phase (single-phasing), which prevents the motor from starting and causes the characteristic loud hum.

(CME) Certified Master Electrician Practice Test

(CME) Certified Master Electrician Practice Test

CME Troubleshooting & Maintenance Techniques 2