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These 10 free QMED questions are organized by exam domain, so you can see how each part of the National QMED: Electrician/Refrigerating Engineer blueprint is tested. Reveal the answer and explanation under each question.
The 24 V DC contactor for a seawater pump will not pick up. During an authorized energized check with START held, the control supply remains at 24 V. A meter shows 19 V across the closed STOP contact and less than 0.2 V across each of the other closed series contacts. These readings identify:
Correct answer: C - High resistance at the STOP contact
Two identical 500 kW generators are paralleled on a ship's isolated bus, with their governors in manual droop operation. No. 1 carries 350 kW and No. 2 carries 150 kW. Frequency and reactive-load sharing are satisfactory. To transfer real load from No. 1 to No. 2 while maintaining bus frequency, the engineer should coordinate which adjustments?
Correct answer: D - Increase No. 2's governor setting and decrease No. 1's
After a motor circuit is isolated and locked out, an electrician proves a voltage tester on a known energized source, then obtains zero on every required phase-to-phase and phase-to-ground test. On the final proving check, the tester also reads zero on the known source, which a second instrument confirms is still energized. May work on the motor terminals begin?
Correct answer: B - No; the failed final proving check invalidates the absence-of-voltage verification
During normal discharge of a flooded lead-acid starting battery, electrolyte specific gravity falls when readings are compared at the same temperature. What chemical change explains this trend?
Correct answer: A - Lead sulfate forms at both plates, consuming sulfuric acid and forming water
A first ground-fault alarm appears on a 440 V, three-wire ungrounded shipboard distribution system. Line-to-line voltages and load currents remain normal, with no smoke, overheating, or protective trip. The bus supplies essential auxiliaries. What is the appropriate initial response?
Correct answer: D - Notify the watch engineer and begin controlled ground-fault localization
A cold room is warming, with low suction pressure, high evaporator superheat, and bubbles in the liquid-line sight glass. Subcooled liquid is confirmed at the filter-drier inlet. The pressure drop across the drier is 18 psi; its normal drop at this flow is less than 2 psi. Which diagnosis accounts for the localized pressure loss as well as the starved evaporator?
Correct answer: B - Restriction in the liquid-line filter-drier
A dry-expansion evaporator uses a refrigerant blend with temperature glide. At the measured evaporator-outlet pressure, the refrigerant chart lists a bubble temperature of -9°C and a dew temperature of -4°C. The pipe temperature at that same location is +3°C. The equipment's specified outlet superheat range is 5-9 K. What does the measurement show?
Correct answer: A - 7 K of superheat, within the specified range
A cold room's thermostat is satisfied and its liquid-line solenoid closes. In this automatic pump-down arrangement, the compressor continues running while suction pressure falls steadily. Suction remains above the specified low-pressure cutout, and oil pressure and discharge temperature are normal. The appropriate response during this interval is to:
Correct answer: D - Allow the compressor to reach the low-pressure cutout
A conventional single-phase hermetic compressor has terminals marked C, R, and S. After electrical isolation, safe capacitor discharge, and removal of all external terminal connections, an ohmmeter reads 3.0 ohms from C to R, open circuit from C to S, and open circuit from R to S. The internal overload, if open, would interrupt the common connection to both windings. Where is the demonstrated open circuit?
Correct answer: C - In the start winding between C and S
An accommodation air-conditioning plant removes moisture by cooling air below its dew point, drains the condensate, and then reheats the air without adding moisture. During reheat at essentially constant pressure, which pair of changes occurs?
Correct answer: A - Unchanged humidity ratio and lower relative humidity
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