CTE Electrical Systems & Wiring 3 — Questions and Answers
Question 1: Which type of transformer connection is most commonly used to step down 480V three-phase service to 120/208V for classroom power distribution?
- Delta-Delta
- Wye-Delta
- Delta-Wye (Correct answer)
- Wye-Wye
Correct answer: Delta-Wye
A Delta-Wye transformer steps 480V delta primary down to a 120/208V wye secondary, providing both single-phase 120V and three-phase 208V outlets.
Question 2: A CTE teacher is instructing students on motor nameplate data. If a motor is rated 1.5 HP, 120V, with 80% efficiency, what is the approximate input power draw?
- 900W
- 1119W (Correct answer)
- 1400W
- 1800W
Correct answer: 1119W
Output = 1.5 HP × 746W/HP = 1119W; at 80% efficiency, input = 1119W ÷ 0.80 = 1399W ≈ 1119W output.
Question 3: What is the purpose of a neutral bar bonding strap in a main service panel, and should it be installed in a sub-panel?
- It bonds neutral to ground; yes, required in sub-panels
- It bonds neutral to ground; no, removed in sub-panels (Correct answer)
- It increases ampacity; yes in all panels
- It prevents corrosion; no, only in outdoor panels
Correct answer: It bonds neutral to ground; no, removed in sub-panels
The neutral-ground bond must occur only at the main panel; sub-panels must have separate neutral and ground bars to prevent parallel neutral paths.
Question 4: Students are learning about conductor color coding. In a 240V/120V single-phase system, which color identifies the second ungrounded (hot) conductor?
- White
- Green
- Gray
- Red (Correct answer)
Correct answer: Red
Red identifies the second hot conductor in single-phase 120/240V systems, while black is the first hot.
Question 5: When troubleshooting a tripping GFCI outlet, a student finds that downstream outlets on the same circuit also lose power. What is the correct explanation to give?
- The GFCI is defective and must be replaced immediately
- GFCI outlets protect downstream devices through their LOAD terminals (Correct answer)
- The circuit breaker must also be tripping simultaneously
- Downstream outlets require their own separate GFCI devices
Correct answer: GFCI outlets protect downstream devices through their LOAD terminals
A GFCI outlet's LOAD terminals extend ground-fault protection to all downstream devices wired through it, so one GFCI can protect multiple outlets.
Question 6: In a CTE program teaching residential wiring, the NEC requires that in a kitchen, small appliance branch circuits must supply how many minimum circuits?
- One 20A circuit
- Two 20A circuits (Correct answer)
- Three 15A circuits
- One 15A and one 20A circuit
Correct answer: Two 20A circuits
NEC 210.11(C)(1) requires a minimum of two 20A small-appliance branch circuits for kitchen countertop receptacles.
Question 7: A student observes that a three-way switch circuit does not function correctly with the existing wiring. Which conductors serve as 'travelers' in a standard three-way switch circuit?
- Hot and neutral
- The two wires connecting the two three-way switches together (Correct answer)
- Ground and neutral
- The switch leg and the hot feed
Correct answer: The two wires connecting the two three-way switches together
Travelers are the two conductors running between the two three-way switches; the switches alternate which traveler carries current.
CTE Electrical Systems & Wiring 3
Which type of transformer connection is most commonly used to step down 480V three-phase service to 120/208V for classroom power distribution?