Troubleshooting & Maintenance Techniques Flashcards
7 cards from real CME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Troubleshooting & Maintenance Techniques flashcards as text
A motor repeatedly trips its overload relay shortly after reset. The motor is running at rated load. What is the MOST likely cause?
Answer: Undersized supply conductors causing voltage drop
Undersized supply conductors cause voltage drop, which increases motor current draw and causes repeated overload trips under rated load conditions.
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?
Answer: The circuit is operating normally with balanced current
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.
A fluorescent lighting circuit has one lamp flickering while adjacent lamps on the same circuit are steady. What should be checked FIRST?
Answer: The lamp, ballast, and lamp holders on the flickering fixture
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.
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?
Answer: 0.1 MΩ per kV of rated voltage plus 1 MΩ
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.
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?
Answer: One phase of the supply is open (single-phasing)
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.
What does a high resistance reading across a closed switch or contactor contact indicate?
Answer: The contacts are burned, pitted, or contaminated
High resistance across closed contacts indicates burned, pitted, or contaminated contact surfaces that impede current flow and cause voltage drop and heat.
A GFCI receptacle will not reset and the test button does not trip it. What is the MOST likely cause?
Answer: The GFCI device has failed and must be replaced
A GFCI that will not reset and whose test button produces no response has an internal failure and must be replaced — the device's self-test circuitry is non-functional.