CME Troubleshooting & Maintenance Techniques 3

Question 1

When performing predictive maintenance using infrared thermography on electrical panels, what temperature differential between similar components typically warrants immediate attention?

Accepted Answer

Greater than 10°C above a similar component under similar load

Answer

A temperature differential greater than 10°C between similar components under similar load conditions is the commonly accepted threshold for immediate corrective action in electrical thermography.

Question 2

A branch circuit shows correct voltage at the panel but low voltage at the last receptacle in a long run. No load is connected. What does this indicate?

Accepted Answer

A high-resistance splice or connection in the circuit

Answer

Voltage drop with no connected load indicates a high-resistance connection (loose splice, corroded terminal) rather than conductor size, since resistive drop under no-load should be negligible.

Question 3

Which test instrument is MOST appropriate for verifying the operation of an arc fault circuit interrupter (AFCI)?

Accepted Answer

A dedicated AFCI circuit tester with a test button

Answer

A dedicated AFCI tester simulates the specific arc fault waveform signature required to trip an AFCI breaker, which standard outlet testers cannot do.

Question 4

During transformer maintenance, a technician notices the mineral oil is darker than normal and has a burnt odor. What does this MOST likely indicate?

Accepted Answer

Internal arcing or overheating of windings or core

Answer

Darkened oil with a burnt odor in a transformer indicates internal arcing or overheating, which produces carbon particles and pyrolysis products that contaminate the oil.

Question 5

A disconnect switch blade shows significant discoloration and pitting at one phase only. After replacing the blade, what additional step is CRITICAL before returning to service?

Accepted Answer

Identify and correct the root cause of the overheating

Answer

Replacing only the damaged component without finding the root cause (loose connection, overloaded circuit, poor contact pressure) will result in recurrence of the same damage.

(CME) Certified Master Electrician Practice Test

(CME) Certified Master Electrician Practice Test

CME Troubleshooting & Maintenance Techniques 3