Free PSE Practice Questions

Question 1

A milled slot gives a controller PCB 8.0 mm of creepage between two conductors, but their shortest separation through air remains 2.6 mm. The applicable requirements are at least 6.4 mm creepage and 3.2 mm clearance; no coating or solid-barrier credit is claimed. Which revision resolves the remaining spacing deficiency?

Accepted Answer

Move the conductors to achieve 4.0 mm clearance while preserving the 8.0 mm creepage path.

Answer

Extend the slot to obtain 10.0 mm creepage while retaining the existing conductor positions.

Answer

Change to a higher-CTI laminate without altering the slot geometry or the conductor positions.

Answer

Apply ordinary solder mask over the conductors and retain both of the measured separation distances.

Question 2

Localized discoloration appears around one terminal during a heater's endurance test. The heater draws 8.0 A rms, the terminal's contact resistance is 0.20 ohm, and its 13 A supply fuse remains intact. Other connections show no abnormal heating. What combination of contact power dissipation and fuse behavior explains these findings?

Accepted Answer

12.8 W at the terminal; localized heating need not produce an overcurrent.

Answer

1.6 W at the terminal; the fuse can remain intact because the load current is below 13 A.

Answer

33.8 W at the terminal; the fuse rating supplies the current used to calculate contact heating.

Answer

12.8 W at the terminal; this added resistance should cause the 13 A fuse to clear an overload.

Question 3

Opening a granulator hood immediately removes motor power, but the cutter remains hazardous for 7 seconds. An operator can reach it within 1.5 seconds. Restart with the hood open is already prevented, and routine loading requires the hood to open. The unresolved design requirement is to:

Accepted Answer

Keep the hood locked until the hazardous cutter motion has ended.

Answer

Add a second opening-detection channel while retaining the same motor stopping behavior.

Answer

Require a deliberate reset after hood closure before permitting the next motor start.

Answer

Fit a hood-mounted emergency-stop button that also removes motor power immediately.

Question 4

Procurement receives a proposal for testing and NRTL certification of a laboratory instrument to UL 61010-1. The bidder's ISO/IEC 17025 accreditation covers the requested tests, but its OSHA NRTL recognition covers UL 62368-1 only. How should the manufacturer distinguish the bidder's testing competence from its certification authority?

Accepted Answer

Its accredited test results can be valid, but its stated NRTL scope does not authorize the requested certification.

Answer

Accreditation for the requested tests automatically extends its NRTL recognition to that standard.

Answer

The manufacturer may apply an NRTL mark after its own engineer reviews the accredited test report.

Answer

Its lack of NRTL recognition for UL 61010-1 prevents it from performing or reporting those tests under its existing laboratory accreditation.

Question 5

The only open finding on an insulation system reads: "Separate basic and supplementary layers cannot be identified." The system separates hazardous live parts from accessible metal and has been evaluated as reinforced insulation for the product's working voltage, environment, and required fault conditions. Which response correctly resolves the reviewer's objection?

Accepted Answer

Accept the reinforced-insulation provision; its protection is equivalent to double insulation.

Answer

Add supplementary insulation; reinforced insulation counts as basic protection.

Answer

Add protective earthing because accessible metal cannot be protected by reinforced insulation without a protective conductor.

Answer

Reclassify the system as functional insulation because basic and supplementary portions cannot be tested separately.

Question 6

A service handbook specifies a 30-second wait followed by voltage verification after all supplies are isolated. To support that wait, a 400 V DC link must decay to 60 V or less within 30 seconds. Its capacitor is 220 microfarads ±20%, and the bleeder resistor is ±5%. Use V(t) = 400 exp[-t/(RC)], with R in ohms and C in farads; neglect other leakage. All candidates have adequate voltage and power ratings. To minimize continuous bleeder loss, select the largest listed nominal resistance that meets the discharge requirement at the worst-case tolerances.

Accepted Answer

47 kilohms

Answer

33 kilohms

Answer

68 kilohms

Answer

82 kilohms

Question 7

A vented housing sits above combustible foam. At the intended wall thickness, both prescribed five-specimen conditioning sets in a UL 94 V-0/V-1/V-2 test have individual afterflame times no greater than 7 seconds, total afterflame time of 42 seconds per set, and combined second-afterflame-plus-afterglow times no greater than 24 seconds. No flame or glow reaches the clamp, but flaming drops ignite the cotton indicator. Which assessment is supported?

Accepted Answer

V-2; ignition of nearby foam still requires a separate construction assessment.

Answer

V-0; the short afterflame times eliminate the need to assess ignition of the foam.

Answer

V-1; brief cotton ignition is permitted when flame and glow do not reach the clamp.

Answer

No V classification; cotton ignition disqualifies all three vertical ratings.

Question 8

The EU compliance plan for a 3 V battery-powered wireless doorbell omits its safety assessment: "The Low Voltage Directive starts at 75 V DC, so safety requirements do not apply." The doorbell is within the Radio Equipment Directive's scope. What correction belongs in the plan?

Accepted Answer

Apply the RED safety objectives; the LVD voltage floor does not apply.

Answer

Assess safety only when a mains-powered charger is included.

Answer

Assess only spectrum use and EMC because the doorbell operates below the LVD voltage range.

Answer

Substitute general consumer-product safety requirements for the RED safety assessment.

Question 9

Door-to-PE resistance on a Class I instrument must not exceed 0.10 ohm under its acceptance procedure. A de-energized four-terminal measurement reads 0.04 ohm with an earthed, shielded data cable connected, but 0.80 ohm after that cable is unplugged. The steel door has a dedicated bonding braid; the test points and verified instrument setup are unchanged. What hidden construction problem does this reveal?

Accepted Answer

The cable shield is providing a parallel path that masks a deficient door bond.

Answer

Test-lead resistance is included despite the four-terminal measurement connection.

Answer

The door requires the data cable as its normal protective connection, so the higher disconnected reading is irrelevant.

Answer

The data cable is correcting an insulation fault by diverting normal mains-filter leakage away from the door.

Question 10

A heater's fault tree models loss of overtemperature shutdown as independent failure of controller A AND controller B. Each controller opens its own series contactor, but both use one thermistor. A credible thermistor fault makes both controllers report a temperature below the trip threshold during overheating. How must the model change to represent this dependency?

Accepted Answer

Add the shared thermistor fault as a single-event path to loss of both shutdown channels.

Answer

Add thermistor failure as a third event required alongside both independent controller failures.

Answer

Split the thermistor failure probability equally between the two independent controller events.

Answer

Keep the model; separate contactors establish independence even with a shared temperature sensor.

Free PSE Practice Questions

Domain 2: Isolation of supply

Question 1

Domain 3: Mechanical hazards

Question 2

Domain 4: Earthing

Question 3

Domain 5: Types of Insulation

Question 4

Domain 7: Resistance to fire

Question 5

Domain 8: Fire hazards

Question 6

Domain 12: Creepage

Question 7

Domain 15: Hazard analysis

Question 8

Domain 18: Legislation US, EEC and International

Question 9

Domain 21: Assessment authorities

Question 10

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