CEP Troubleshooting & System Testing 3

Question 1

A transformer secondary voltage reads 10% below nameplate value at full load but is correct at no load. The most likely cause is:

Accepted Answer

Excessive transformer winding impedance causing voltage drop under load

Answer

Voltage regulation — the difference between no-load and full-load voltage — is directly caused by the transformer's internal impedance interacting with load current.

Question 2

When troubleshooting an intermittent nuisance trip on a 100A molded-case circuit breaker, which test method is most appropriate?

Accepted Answer

Infrared thermography scan under normal load conditions

Answer

Infrared thermography can identify loose connections or high-resistance joints that cause localized heating, which is a common cause of intermittent MCCB trips.

Question 3

A 480V/277V wye-connected distribution system shows a sustained neutral-to-ground voltage of 8V under balanced load. This indicates:

Accepted Answer

A high-resistance connection in the neutral conductor

Answer

A neutral-to-ground voltage above ~2–3V under balanced load indicates a high-resistance neutral connection creating a voltage drop along the neutral conductor.

Question 4

During commissioning of a large UPS system, the static bypass switch fails to transfer load from UPS output to bypass. The FIRST check should be:

Accepted Answer

Verify the bypass source voltage and phase angle are synchronized with UPS output

Answer

The static bypass switch requires the bypass source and UPS output to be phase-synchronized before a bumpless transfer can occur.

Question 5

A resistance temperature detector (RTD) on a motor bearing reads 4000 Ω at room temperature when it should read approximately 109.8 Ω. This suggests:

Accepted Answer

An open circuit in the RTD or its lead wires

Answer

A PT100 RTD should read near 100 Ω at 0°C and rises only slightly with temperature; a reading of 4000 Ω indicates an open circuit in the element or lead wiring.

(CEP) Certified Electrical Professional Practice Test

(CEP) Certified Electrical Professional Practice Test

CEP Troubleshooting & System Testing 3