CEP Troubleshooting & System Testing 5

Question 1

During commissioning of a fire alarm system, all smoke detectors on a loop show a trouble condition immediately after installation. The most likely cause is:

Accepted Answer

An end-of-line resistor is missing or has incorrect value

Answer

Addressable and conventional fire alarm loops require a proper end-of-line resistor to establish correct loop supervision; a missing or wrong-value resistor causes a trouble fault on the entire loop.

Question 2

A ground-fault protection relay on a 480V solidly-grounded system operates at 5A sensitivity. A line-to-ground fault of 300A occurs. The relay should:

Accepted Answer

Operate because fault current exceeds pickup of 5A

Answer

Ground-fault relays operate when zero-sequence current exceeds their pickup setting; a 300A fault far exceeds the 5A pickup, so the relay will operate.

Question 3

An infrared scan of a 600A fusible disconnect reveals the phase B fuse clips are 40°C hotter than phases A and C under balanced load. The recommended action is:

Accepted Answer

Immediately de-energize, inspect and tighten or replace the fuse and clips

Answer

A 40°C temperature differential is a serious finding indicating high contact resistance that can lead to fuse failure, fire, or arc flash; immediate corrective action is required.

Question 4

A technician is verifying the operation of a transfer switch that moves a critical load from utility to generator. After a utility outage, the load transfers but a 6-second delay occurs before the generator feeds the load. This delay is:

Accepted Answer

Caused by the generator reaching rated voltage and frequency before transferring

Answer

Automatic transfer switches include a generator time delay to allow the genset to stabilize at rated voltage and frequency before closing the transfer switch onto the load.

Question 5

A variable frequency drive faults on 'DC bus overvoltage' during motor deceleration. The most effective corrective solution is:

Accepted Answer

Increase deceleration ramp time to allow energy to dissipate

Answer

During deceleration, the motor acts as a generator, pumping energy back into the DC bus; extending the decel ramp time reduces the rate of energy return and prevents overvoltage trips.

(CEP) Certified Electrical Professional Practice Test

(CEP) Certified Electrical Professional Practice Test

CEP Troubleshooting & System Testing 5