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iec year 2 part 3 EXAM TEST BANK
WITH ALL VERSIONS OF THE EXAM
WITH ALLMODULES COVERED |
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1. When a large service is built, CT cans are utilized. These enclosures contain ___ transformers. A. Voltage B. Power C. Current D. Step-down ✅ Correct Answer: C. Current Rationale: CT cans house Current Transformers used for metering and protection in large services. 2. Large dry-type distribution transformer enclosures have steel bottoms that are punched for ___. A. Conduits B. Wires C. Screws D. Ventilation ✅ Correct Answer: D. Ventilation Rationale: Per NEC, ventilation holes dissipate heat from the transformer. 3. When a transformer’s windings are encapsulated, the resin encapsulation ___. A. Protects against moisture B. Reduces sound C. Increases mechanical strength D. All of the above ✅ Correct Answer: D. All of the above Rationale: Resin encapsulation provides insulation, noise reduction, and protection. 4. A transformer enclosure that is ventilated ___ air from outside the enclosure to circulate through it. A. Blocks B. Filters
C. Does not allow D. Does allow ✅ Correct Answer: D. Does allow Rationale: Ventilated enclosures are designed to allow airflow for cooling.
5. An example of an autotransformer is a ___. A. Buck-boost transformer B. Variac C. Isolation transformer D. Both A and B ✅ Correct Answer: D. Both A and B Rationale: Buck-boost and variac types use a common winding like autotransformers. 6. A step-down transformer’s secondary winding is connected to ___. A. Ground B. The supply C. The load D. The neutral ✅ Correct Answer: C. The load Rationale: The secondary supplies power to the load at a lower voltage. 7. An ___ has no direct electrical connection between primary and secondary windings. I. Autotransformer II. Isolation transformer A. I only B. II only C. Both I and II D. Neither ✅ Correct Answer: B. II only Rationale: Only isolation transformers have electrically isolated windings. 8. Dry-type transformer insulation is based on an ambient temperature of ___°C. A. 25 B. 30 C. 40 D. 55 ✅ Correct Answer: C. 40 Rationale: Industry standard insulation class is based on 40°C ambient. 9. A transformer with a ___ enclosure is permitted to be installed inside a building. A. Ventilated
14. When operated within its ratings, a transformer can be expected to operate for about ___ years. A. 10– 15 B. 20– 25 C. 5– 8 D. 30– 35 ✅ Correct Answer: B. 20– 25 Rationale: Transformers are typically designed for 20–25 years of service when not overloaded. 15. A transformer requires 32 amps at 480 volts on the primary to deliver 120-volt power to a 14.6 kW load. The efficiency of this transformer is ___%. A. 90 B. 92 C. 95 D. 98 ✅ Correct Answer: C. 95 Rationale: Efficiency = Output/Input power = 14.6 kW / (480V × 32A) ≈ 0.95 or 95%. 16. A new transformer must be sized at 125% of the existing 79.2 kVA load. The minimum calculated size is ___ kVA. A. 89 B. 92 C. 99 D. 105 ✅ Correct Answer: C. 99 Rationale: 79.2 × 1.25 = 99 kVA. 17. Turns ratio can be written as ___. A. Primary:Secondary B. Voltage ratio C. Number of turns D. Any of these ✅ Correct Answer: D. Any of these Rationale: The turns ratio can be expressed in various forms depending on context— number of turns, voltage ratio, or current ratio. 18. A 120 VA load is the only load connected to the secondary of a 250 VA transformer. To supply this load, the transformer must be supplied with at least ___ VA of power on the primary. A. 250 B. 200 C. 120 D. 100
✅ Correct Answer: C. 120 Rationale: The primary must provide at least what the load demands—120 VA.
19. A CT with a current ratio of 500:1 is used in a metering circuit. If the meter shows 67 mA, the actual current is ___ amps. A. 33. B. 67 C. 500 D. 134 ✅ Correct Answer: A. 33. Rationale: 0.067 A × 500 = 33.5 A in the primary circuit. 20. A transformer has a 240 V primary and a 120 V secondary. A 10 A load on the secondary draws how much primary current? A. 5 A B. 10 A C. 15 A D. 20 A ✅ Correct Answer: A. 5 A Rationale: Power is conserved: 240 V × I = 120 V × 10 A → I = 5 A. 21. Transformers are rated in ___ indicating maximum output power. A. kW B. HP C. VA D. V ✅ Correct Answer: C. VA Rationale: Transformers are rated in Volt-Amperes (VA) because they handle apparent power. 22. A 1Ø transformer rated at 500 VA can supply ___ amps at 120 volts. A. 2. B. 3. C. 4. D. 5. ✅ Correct Answer: C. 4. Rationale: Current = Power / Voltage = 500 / 120 = 4.17 A. 23. A 120 V primary, 12 V secondary transformer has a turns ratio of ___ to 1. A. 5 B. 10 C. 15 D. 20
✅ Correct Answer: B. 5: Rationale: 120 / 24 = 5:1 ratio.
29. A 15 kVA transformer supplying an 11.5 kW load at 120 V delivers ___ amps. A. 85. B. 95. C. 100 D. 120 ✅ Correct Answer: B. 95.83 A Rationale: I = P / V = 11,500 / 120 = 95.83 A. 30. Which statement is true about transformers? A. Voltage and current are inversely proportional B. Power in primary equals power in secondary (minus losses) C. Both A and B D. Neither A nor B ✅ Correct Answer: C. Both A and B Rationale: Transformer principles include conservation of power and inverse voltage- current relationship. 31. A transformer with 120 V primary and 24 V secondary receives only 100 V input. The output voltage is ___. A. 20 V B. 18 V C. 22 V D. 24 V ✅ Correct Answer: A. 20 V Rationale: Proportional voltage drop: (100/120) × 24 = 20 V. 32. Using an ohmmeter between transformer terminals X1 and H2, the reading would be: A. 0 Ω B. Infinite (OL) C. 12 Ω D. 120 V ✅ Correct Answer: B. Infinite (OL) Rationale: Primary and secondary are isolated, so resistance is infinite (no continuity). 33. A transformer rated 130 V primary, 16 V secondary receives 110 V. Output voltage is ___. A. 12 B. 13. C. 16
D. 10
✅ Correct Answer: B. 13.54 V Rationale: (110 / 130) × 16 = 13.54 V.
34. A 120 V primary with 24 V secondary and 2 A primary current yields secondary current of: A. 2 A B. 4 A C. 10 A D. 12 A ✅ Correct Answer: C. 10 A Rationale: Power is constant → 120 × 2 = 240 W; secondary I = 240 / 24 = 10 A. 35. A transformer delivers 332 A at 240 V. It is supplying ___ kVA. A. 72 B. 79. C. 84 D. 100 ✅ Correct Answer: B. 79.68 kVA Rationale: kVA = (332 × 240) / 1000 = 79.68 kVA. 36. A 120 V primary, 16 V secondary transformer with 1.1 A primary current implies ___ A secondary current. A. 5 B. 8. C. 6 D. 10 ✅ Correct Answer: B. 8.25 A Rationale: 120 × 1.1 = 132 W; 132 / 16 = 8.25 A. 37. Two 120/240 V transformer secondary windings connected for 240 V are in ___. A. Parallel B. Series C. Wye D. Delta ✅ Correct Answer: B. Series Rationale: Series connection combines voltages for 240 V operation. 38. A 25 kVA 120/240 V transformer delivers ___ amps at 240 V. A. 62. B. 83. C. 104
A. 1
B. 2.
C. 5
D. 10
✅ Correct Answer: B. 2. Rationale: 2.5% is standard step size in tap settings for fine voltage adjustment.
44. For a 1Ø transformer with dual-voltage secondary, power rating is total power ___ can supply. A. One winding B. The higher voltage side C. The lower voltage side D. Both secondary windings ✅ Correct Answer: D. Both secondary windings Rationale: The total transformer rating includes power from both windings. 45. For a 1Ø transformer with dual-voltage secondary, the voltages induced in each winding are equal. A. True B. False ✅ Correct Answer: A. True Rationale: Windings are identical; voltages are the same unless connected differently. 46. Which secondary transformer connection (Figure 215.52) supplies correct voltage to a 120 V load? A. I B. II C. III D. IV ✅ Correct Answer: B. II Rationale: Connection II shows parallel windings for 120 V output. 47. Which secondary transformer connection (Figure 215.52) supplies correct voltage to a 240 V load? A. I B. II C. III D. IV ✅ Correct Answer: A. I Rationale: Connection I shows series configuration for 240 V output. 48. When the ___ voltage differs from the rated voltage, transformer taps can be used to correct output voltage.
A. Secondary B. Primary C. Load D. Neutral ✅ Correct Answer: B. Primary Rationale: Taps on the primary side adjust for input voltage variation.
49. Refer to Figure 216.21. The transformer feeding MDP must supply ___ volts to the Main Distribution Panel. A. 208 B. 240 C. 120/ D. 480 ✅ Correct Answer: C. 120/ Rationale: Based on panel and switch loads listed, a 1Ø 3W 120/240 V supply is needed. 50. A 480–120/240 V transformer is supplied with 496 V. The expected line-to- neutral output voltage is ___. A. 120 V B. 122 V C. 124 V D. 126 V ✅ Correct Answer: C. 124 V Rationale: Higher input raises output proportionally: (496/480) × 120 = 124 V. 51. Voltage taps on the transformer primary are used when input voltage is ___ rated voltage. A. Equal to B. Higher than C. Lower than D. Either B or C ✅ Correct Answer: D. Either B or C Rationale: Taps adjust for both overvoltage and undervoltage conditions. 52. A 240/480 V primary – 120/240 V secondary transformer can connect to a 2- pole breaker in a ___ panelboard and still deliver nameplate-rated voltage. A. 120 V B. 240 V C. 480 V D. B or C only ✅ Correct Answer: D. B or C only
___ surrounds the windings in typical 75 kVA dry-type distribution transformers. - Ans - Air OSHA ___ sets forth standards for fall protection training. - Ans - 1926. OSHA has standards for which of the following? - Ans - both a and b The most frequently cited OSHA construction standards change ___ from year to year. - Ans - little The general duty clause of the OSHA standard requires ___ employer(s) to provide to each of his employees, a place of employment that is free of hazards which are likely to cause death or serious harm to his employees. - Ans - each OSHA 1926.451 covers ___. - Ans - scaffold access The Powered Industrial trucks standard covers ___ plus operator training and operation.I. forklifts II. motorized hand trucks III. material handling equipment - Ans - I, II & III The OSHA ___ standard is violated more than any other in construction work and even has two standards. - Ans - Fall Protection Many three-phase generators can be connected to deliver output voltage configurations such as ___. - Ans - both a and b The rated power output (capacity) of a transformer is given on the nameplate in ___. - Ans - kVA In three-phase systems, the voltage between any two ungrounded conductors is equal. This voltage is known as ___. - Ans - any of these Which of the following statements is true of wye-configured voltage systems? - Ans - Icoil = Iline A three-phase generator has three sets of magnets on the rotor. These are mounted so that they ___. - Ans - are offset 120° from each other Which of the following statements is true of delta-configured voltage systems? - Ans - Icoil = Iline / 1.
The following are examples of a slash-rated three-phase system except for ___. - Ans - 480V three-phase, three-wire Three-phase, four-wire systems can provide power to the following loads: - Ans - all of these If the higher voltage of a slash-rated three-phase voltage system equals twice the lower voltage, the system is ___. - Ans - delta-connected When a 3Ø, 4-W supply system delivers 120/208 volts, the system is ___ connected. - Ans - wye A 480-volt 3-phase circuit is connected to the delta primary of a 480 to 240-volt 3-phase transformer. The voltage across any one primary winding is ___ volts. - Ans - 480 Which of the following is a type of electric power generating plant? - Ans - All of these Substations are used to ___. - Ans - either a or b When a 3Ø, 4-W supply system delivers 120/240 volts, the system is ___ connected. - Ans - delta When a 3Ø, 4-W supply system (typically a transformer) delivers 120/240 volts, the system has line-to-line voltages that are ___ volts. - Ans - 240 When a 3Ø, 4-W supply system (typically a transformer) delivers 120/240 volts, the system has BØ-to-neutral voltages that are ___ volts. - Ans - 208 Inverters are required to convert the output energy from ___ to AC. - Ans - solar arrays Which of these are typical high transmission voltages? - Ans - 230 kV When a 3Ø, 3-W supply system delivers 240 volts, the system is ___ connected. - Ans - delta When a 3Ø, 4-W supply system delivers 277/480 volts, the system has line-to-line voltages that are ___ volts. - Ans - 480 If the output of a 3Ø generator is 240 volts, line-to-line, and it has a neutral connection, this is a ___ system. - Ans - 3Ø, 4-W When a 3Ø, 4-W supply system delivers 277/480 volts, the system is ___ connected. - Ans - wye
A 208-volt, 17.2 KVA, single-phase load is connected to a 120/208-volt, three-phase, 4wire panel. The load will draw ___ amps at the applied voltage. - Ans - 82. A certain 3-phase load draws 27.8 amps and is operating on a circuit that is fed from a 120/240-volt 3-ph, 4-W panelboard. This load is using ___ kVA of power. - Ans - 11. A 3Ø 240-volt load is supplied power by a 100 KW generator. The nameplate rating on the load is 59.2 KVA. The line (circuit) conductors between the generator and the load will be carrying ___ amps. - Ans - 142 A 3Ø, 480-volt, 45 KVA, wye-connected load draws ___ a 3Ø, 480-volt, 45 KVA, deltaconnected load. - Ans - the same line current as A three-phase 69 KVA load will be connected to a circuit that is fed from a 3-pole breaker in a 120/240-volt 3Ø, 4-wire panel. This load will draw ___ amps of current through each circuit conductor. - Ans - 166 A certain 3-phase load draws 37.3 amps and is operating at 208 volts. This load is using ___ KVA of power. - Ans - 13. Three-phase loads of 16, 42, and 75 amps are fed from a 240-volt panel. This total 3Ø load is ___ kVA. - Ans - 55. The ___ shall determine if the walking/working surface has strength and structural integrity to support employees safely. - Ans - employer Each employee at the edge of ___ or similar excavation 6 feet or more in depth shall be protected from falling by guardrail systems, fences, or barricades.I. a pit II. a well III. a shaft - Ans - I or II or III Each employee in a hoist area shall be protected from falling 6 feet or more to a ___ by guardrail systems or personal fall arrest systems. - Ans - lower level When working over dangerous equipment that one could fall onto or into, one must be protected by guardrail systems, ___, or personal fall arrest systems. - Ans - machine guards Falls are the number ___ cause of construction deaths. - Ans - one Each employee on a walking/working surface with an unprotected side or edge which is 6 feet or more to a lower level shall be protected from falling by use of ___ systems.I. personal fall arrest II. guardrail III. safety net - Ans - I or II or III
The OSHA subpart on Fall Protection has many ___ that outline numerous methods to accomplish safe means to work at heights. - Ans - requirements If an employee can fall through a ___ 6 feet or more to a lower level the employee has to be protected by personal fall arrest systems, covers over the holes, or guardrail systems. - Ans - hole A ___ connection requires that the single-phase transformers be interconnected so that X1 of one transformer is connected to X2 of the next. - Ans - delta A(n) ___ delta is a variation of a three-phase, four-wire system that only utilizes two transformers. - Ans - open When equipment, a system, or a circuit has a delta or wye designation, the equipment, system, or circuit is ___. - Ans - three-phase In a three-phase four-wire delta system, the B-phase conductor is known as the ___ and is connected to the middle busbar in the panel. - Ans - high-leg If 120-volt loads are required to be connected to a delta transformer, one of the three output coils has a ___ so that two 120-volt outputs are available. - Ans - center-tap When the supply voltage is higher or lower than the nameplate rated primary voltage of a transformer ___. - Ans - it will result in a higher or lower-than-nameplate rated secondary voltage The connected load on the secondary of a transformer causes current to flow in the ___. - Ans - all of these In a three-phase transformer, if a voltage higher than the nameplate rated voltage is applied to the primary, a voltage ___ the nameplate rated secondary voltage will be delivered to a load. - Ans - higher than When transformers are installed to adjust voltage for a customer's needs, they can be configured to ___. - Ans - either of these If a transformer has a delta primary and a wye secondary, the transformer is referred to as a ___ transformer. - Ans - delta-wye In a corner-grounded delta, the grounded conductor is referred to as the ___. - Ans - dead man's leg If the load connected to the secondary of a delta-connected transformer is balanced, the coil currents are equal in each of the three windings. - Ans - True
Figure 220.401 Refer to Figure 220.401. The transformer bank has each of its secondary ("X") windings connected in ___. - Ans - series Figure 220.402 Each transformer in the bank, shown in Figure 220.402, is rated to deliver 120/240 when rated primary voltage is applied. Which diagram shows the correct connections for a 120/240-volt, 3-ph, 4-wire secondary? - Ans - I only Where a delta bank of three transformers is installed to serve a load that is comprised mostly of 120-volt loads (balanced), each power transformer must supply ___ required by the 120-volt loads. - Ans - about a third of the current When a 3Ø, 4-W supply system (typically a transformer) delivers 120/240 volts, the system has coil (or winding) voltages that are ___ volts. - Ans - 240 A ___ output could be produced by connecting three individual 240 ´ 480 - 120/240 volt single-phase transformers into a bank.I. 240 volt 3Ø, 3-wire II. 120/240 volt 3Ø, 4 wire - Ans - either I or II A 3Ø transformer supplies 120/240 volts to a 3Ø, 4-wire panelboard. From the breaker in space ___, there will be 208 volts to ground (or neutral). - Ans - 10 Scenario 220.21A 3Ø transformer bank supplies 120/240 volts to a 3Ø, 4-wire panelboard. There is a 30 kVA 3Ø load connected to a 3-pole breaker in spaces 1- 3 - 5. There is a 240-volt 15 kW load connected to a 2-pole breaker in spaces 2-4. There is a 120 - volt 10 kW load connected to a 1-pole breaker in space 6. Refer to Scenario 220.21. If all the loads are operating and a clamp-on ammeter were placed around the AØ feeder conductor to the panel, there should be ___ amps of current flowing in the feeder conductor. - Ans - 134. Scenario 220.23 A closed-delta bank of transformers delivers 120/240-volt power to several loads. The 1-phase loads are drawing 120 amps on AØ and 120 amps on CØ. The bank is also supplying power to a 3Ø load that draws 46 amps.Refer to Scenario 220.23. The approximate calculated size required for the "lighting" transformer(s) has a rating of ___ KVA. - Ans - 26 When a 120/240-volt 3Ø, 4-W supply system (typically a transformer) delivers power to a load, the line current equals ___. - Ans - Icoil (or winding) x 1. ___-connected primaries are more common. - Ans - Delta A bank of three 100 KVA transformers is delivering 120/240 volts to a building service. This bank can deliver ___ amps of current to the service if one of the transformers goes out. - Ans - 417
When a 120/240-volt, 3Ø, 4-W open-delta bank of transformers delivers power to a load, the line voltage equals ___. - Ans - Ecoil (or winding) An open-delta bank of transformers uses 100 KVA transformers. This bank can deliver a maximum of ___ kVA of power. - Ans - 173 When a 120/240-volt, 3Ø, 4-W open-delta bank of transformers delivers power to a load, the line current equals ___. - Ans - Icoil (or winding) When a 120/240-volt, 3Ø, 4-W open-delta bank of transformers delivers power to a load, the BØ-to-neutral voltage is ___ volts. - Ans - 208 Refer to Figure 220.301 where the secondary voltage is 240 volts. This is a(n) ___ transformer bank. - Ans - open delta When a 120/240-volt, 3Ø, 4-W open-delta bank of transformers delivers power to a load, the AØ-to-neutral voltage is ___ volts. - Ans - 120 An open-delta bank of transformers delivers ___ power. - Ans - 3Ø When a 120/240-volt, 3Ø, 4-W open-delta bank of transformers delivers power to a load, the AØ-to-CØ voltage is ___ volts. - Ans - 240 Three-phase loads of 16, 42, and 75 amps are fed from a 208-volt panel. This total 3Ø load is ___ KVA. - Ans - 47. When a 120/208-volt, 3Ø, 4-W supply system (typically a transformer) delivers power to a load, the line voltage equals ___. - Ans - Ecoil (or winding) x 1. When a 277/480-volt, 3Ø, 4-W supply system (typically a transformer) delivers power to a load, the coil (or winding) current equals ___. - Ans - IL When a 120/208-volt, 3Ø, 4-W supply system (typically a transformer) delivers power to a load, the coil (or winding) voltage equals ___. - Ans - EL ÷ 1. A 3Ø, 45 KVA load will be supplied power by a 3Ø, 480 to 120/208-volt "Y" transformer bank. This transformer bank must have a 3Ø rating of at least ___ KVA. - Ans - 45 When a 3Ø, 4-W supply system (typically a transformer) delivers 277/480 volts, the system has line-to-neutral voltages that are ___ volts. - Ans - 277 If the output of a 3Ø generator is 208 volts, line-to-line, and it has a neutral connection, this is a ___ system. - Ans - 3Ø, 4-W
