Second Year IEC Final TEST QUESTIONS ALL VERSIONS 2025 | LATEST AND ACCURATE REAL EXAM QUESTIONS WITH DETAILED ANSWERS | VERIFIED FOR GUARANTEED PASS | LATEST UPDATE

In reality, transformer efficiency can never be 100% because of: • A. Eddy-current losses • B. Copper losses • C. Both A and B • D. Hysteresis losses only Correct Answer: C. Both A and B Rationale: Transformer inefficiency is mainly due to copper losses in the windings and eddy-current losses in the core. Transformers power ratings can be in: • A. VA • B. MVA • C. KVA • D. All of the above Correct Answer: D. All of the above Rationale: Transformer ratings are commonly expressed in volt-amperes (VA), kilovoltamperes (KVA), or megavolt-amperes (MVA), depending on size. Most commonly, the supply circuit to a transformer is connected to the leads, terminals, or lugs marked as the: • A. Secondary • B. Ground C. Primary • D. Load Correct Answer: C. Primary Rationale: The input side where power is supplied to a transformer is called the primary winding. The principle upon which transformers operate is: • A. Static electricity • B. Resistance heating • C. Electromagnetic induction • D. Thermoelectric generation Correct Answer: C. Electromagnetic induction Rationale: Transformers function based on electromagnetic induction, where a changing magnetic field induces voltage. A transformer's primary winding and secondary winding are actually connected together. • A. True • B. False Correct Answer: B. False Rationale: The primary and secondary windings are electrically isolated from each other and linked through a magnetic field. A load that uses 6.2 KW of power is using _____ watts. • A. 0.62 • B. 0.062 • C. 0.620 • D. 6.2 • E. None of these Correct Answer: E. None of these Rationale: 6.2 KW equals 6200 watts, which is not listed among the options. Generally transformers have an efficiency of more than 90%. • A. True • B. False Correct Answer: A. True Rationale: Most modern transformers achieve efficiency levels greater than 90%, especially at full load. The efficiency of the transformer described (15.9A at 480V supplying 7.4 KVA at 240V) is: • A. 94.87% • B. 96.96% • C. 92.15% • D. 89.54% Correct Answer: B. 96.96% Rationale: Given values and calculations indicate an efficiency of 96.96%. ______ in utility transmission lines reduces the power losses in the transmission conductors. • A. Lowering current • B. Increasing frequency • C. Increasing the voltage • D. Decreasing resistance Correct Answer: C. Increasing the voltage Rationale: Increasing voltage reduces current and, therefore, I²R losses in conductors. Temperature _____ is the difference in temperature between the transformer windings and the ambient temperature. • A. drop • B. spike • C. surge D. rise Correct Answer: D. rise Rationale: Temperature rise measures the heat developed by a transformer compared to ambient. 40°C = _____ °F • A. 98.6 • B. 120 • C. 104 • D. 100 Correct Answer: C. 104 Rationale: 40°C is equal to 104°F (using the conversion formula F = 9/5C + 32).* When a transformer is loaded beyond its rating the effects are: • A. Excessive temperature • B. Deterioration of insulation • C. Coil failure • D. All of the above Correct Answer: D. All of the above Rationale: Overloading a transformer causes heat buildup, insulation breakdown, and potential winding failure. Dry-type distribution transformers are equipped with _____ to reduce mechanical noise due to vibration. • A. Ballasts • B. Dampers • C. Isolation pads • D. Rubber grommets Correct Answer: C. Isolation pads Rationale: Isolation pads are used to minimize vibration-related noise. If rated voltage is applied to the primary of a small transformer with compensation in its secondary, the secondary voltage will be: • A. Lower • B. Equal • C. Fluctuating • D. Higher Correct Answer: D. Higher Rationale: Small transformers may have slightly higher secondary output due to built-in compensation. You must use a transformer built specifically for step-up applications to change from 240 volts to 480 volts. • A. True • B. False Correct Answer: B. False Rationale: Many transformers are bidirectional in operation as long as voltage/current ratings are respected. A 240/480V primary and 120/240V secondary transformer can be connected to a 2-pole breaker in a: • A. 120/240V 3-phase 4-wire panel • B. 277/480V 3-phase 4-wire panel • C. Either of the above • D. Neither Correct Answer: C. Either of the above Rationale: The transformer can be used with both types of panelboards depending on configuration. Minimum KVA size needed for listed loads: • A. 6.75 KVA B. 7.25 KVA C. 7.92 KVA D. 8.10 KVA Correct Answer: C. 7.92 KVA Rationale: The total calculated load equates to 7.92 KVA based on circuit currents. If two 1-phase conductors from a 100 KVA, 1.8% Z transformer are shorted, approx. how many amps will flow? • A. 18,450 • B. 19,880 • C. 23,148 • D. 20,000 Correct Answer: C. 23,148 Rationale: Using the short-circuit current formula, the calculated fault current is about 23,148A. Demand Factor is defined as: • A. Total load ÷ connected load • B. Connected load ÷ actual use • C. Maximum demand ÷ connected load • D. None of the above Correct Answer: C. Maximum demand ÷ connected load Rationale: The demand factor is the ratio of the highest usage to total possible connected load. The ______ rating is the ampere rating or setting of the overcurrent device protecting the conductors. • A. Feeder • B. Panelboard • C. Branch circuit D. Service Correct Answer: C. Branch circuit Rationale: The branch circuit rating limits the ampacity of conductors it protects. General lighting loads for dwelling units are calculated at: • A. 2 VA per square foot • B. 3 VA per square foot • C. 5 VA per square foot • D. 180 VA per square foot Correct Answer: B. 3 VA per square foot Rationale: Per NEC, dwelling general lighting is calculated at 3 VA/ft². Each receptacle on a single strap is calculated at: • A. 90 VA • B. 150 VA • C. 180 VA • D. 120 VA Correct Answer: C. 180 VA Rationale: NEC requires 180 VA per receptacle.