Electrical Circuits
15 free questions with worked answers, and 161 more in the full bank.
Free questions
A technician is running a new 50A branch circuit to a range. They pull 8 AWG THHN copper wire through an attic where the ambient temperature reaches 120°F. During inspection, the installation fails. Why?
4 marks · Hard
While remodeling a residential bathroom, an apprentice wires a new 20A receptacle directly to the vanity light switch circuit without GFCI protection. What specific code violation has occurred?
3 marks · Medium
A homeowner complains that a newly installed bedroom outlet trips the breaker whenever a lamp is turned on. The panel has a dual-function AFCI/GFCI breaker. What is the most likely cause?
1 mark · Easy
During an inspection of a commercial kitchen, you notice the 125V, 15A receptacles near the sinks lack GFCI protection. The manager claims they are exempt because they are dedicated for refrigerators. How should you respond?
3 marks · Medium
An electrician installs a 100A subpanel in a detached garage using a 3-wire feeder (two hots, one neutral) and bonds the neutral to the ground bus at the subpanel. What is the primary safety risk here?
4 marks · Hard
A maintenance tech uses a megohmmeter to test a 480V 3-phase pump motor. The reading from phase A to ground is 0.5 MΩ. What should the tech conclude?
3 marks · Medium
You place a clamp-on ammeter around an extension cord powering a running 12A space heater, but the meter reads 0.00A. What is the reason for this reading?
1 mark · Easy
A technician measures voltage at a standard 120V receptacle and gets 120V between hot and neutral, but 0V between neutral and ground, and 60V between hot and ground. What is the most likely fault?
3 marks · Medium
When checking a 3-phase panel, you read 120V from Phase A to Neutral, 120V from Phase B to Neutral, and 208V from Phase C to Neutral. What type of electrical system are you testing?
4 marks · Hard
An industrial oven keeps tripping its breaker intermittently. A tech checks the amp draw and finds it steady at 38A on a 40A breaker. Why is the breaker tripping?
3 marks · Medium
You are replacing a 10 HP, 460V, 3-phase motor. The nameplate lists the Full Load Amps (FLA) as 14.0A and the Service Factor as 1.15. What is the maximum setting for the overload relays according to general NEC rules?
3 marks · Medium
A large induction motor utilizes a star-delta starter to reduce inrush current. During the start sequence, the motor starts in star but trips the main breaker the exact moment it transitions to delta. What is the most likely cause?
4 marks · Hard
An operator reports that a 3-phase conveyor motor is "humming loudly and getting extremely hot" but not turning. Voltage measurements at the motor peckerhead show 480V between L1-L2, 0V between L2-L3, and 0V between L1-L3. What is happening?
3 marks · Medium
When wiring a dual-voltage (230/460V) 9-lead 3-phase motor for high voltage (460V), how should the windings be connected?
1 mark · Easy
A technician is sizing the branch circuit conductors for a single 25 HP, 460V, 3-phase motor with a table FLC of 34A. What is the minimum ampacity required for these conductors?
3 marks · Medium
More Electrical Circuits questions (page 2 of 3)
Answers and explanations are in the full bank.
- If the length of a conductor is doubled with the same cross-section, what happens to its resistance? · 3 marks
- In a TVET training workshop four loads are measured: 12 V across 76 Ω, 110 V across 70 Ω, 230 V across 74 Ω, 12 V across 45 Ω. Which draws the largest current? · 3 marks
- If the current through a fixed resistor is doubled, what happens to the power dissipated? · 3 marks
- Equipment in a health-centre server room runs at 230 V and draws 2.1 A. What power does it consume? · 1 mark
- In a hospital IT room four loads are measured: 110 V across 51 Ω, 12 V across 62 Ω, 24 V across 107 Ω, 12 V across 36 Ω. Which draws the smallest current? · 3 marks
- In a Kigali district office four loads are measured: 400 V across 78 Ω, 110 V across 96 Ω, 110 V across 86 Ω, 230 V across 55 Ω. Which dissipates the least power? · 3 marks
- Equipment in a hospital IT room runs at 230 V and draws 12.9 A. What power does it consume? · 1 mark
- In a hospital IT room four loads are measured: 12 V across 98 Ω, 12 V across 56 Ω, 12 V across 22 Ω, 230 V across 79 Ω. Which draws the largest current? · 3 marks
- In a TVET training workshop four loads are measured: 110 V across 95 Ω, 48 V across 53 Ω, 24 V across 94 Ω, 400 V across 88 Ω. Which draws the smallest current? · 3 marks
- In a health-centre server room four loads are measured: 110 V across 60 Ω, 12 V across 37 Ω, 400 V across 22 Ω, 48 V across 37 Ω. Which dissipates the most power? · 3 marks
- In a hospital IT room four loads are measured: 110 V across 20 Ω, 24 V across 59 Ω, 110 V across 5 Ω, 230 V across 24 Ω. Which dissipates the least power? · 3 marks
- If a second identical resistor is added in parallel, what happens to the total resistance? · 3 marks
- In a school computer lab four loads are measured: 24 V across 39 Ω, 110 V across 61 Ω, 400 V across 91 Ω, 48 V across 114 Ω. Which dissipates the least power? · 3 marks
- Equipment in a TVET training workshop runs at 230 V and draws 13.7 A. What power does it consume? · 1 mark
- In a sector office network four loads are measured: 230 V across 18 Ω, 12 V across 91 Ω, 48 V across 36 Ω, 48 V across 53 Ω. Which dissipates the least power? · 3 marks
- If the frequency of a supply is doubled, what happens to the period? · 3 marks
- In a school computer lab four loads are measured: 48 V across 22 Ω, 24 V across 26 Ω, 12 V across 24 Ω, 12 V across 70 Ω. Which draws the smallest current? · 3 marks
- If the resistance is doubled with the voltage unchanged, what happens to the current? · 3 marks
- In a Kigali district office four loads are measured: 230 V across 7 Ω, 400 V across 65 Ω, 24 V across 120 Ω, 24 V across 44 Ω. Which draws the smallest current? · 3 marks
- If a second identical resistor is added in series, what happens to the total resistance? · 3 marks
- If the supply voltage is doubled with the resistance unchanged, what happens to the power dissipated? · 3 marks
- In a hospital IT room four loads are measured: 12 V across 16 Ω, 12 V across 39 Ω, 400 V across 42 Ω, 110 V across 104 Ω. Which dissipates the most power? · 3 marks
- In a health-centre server room four loads are measured: 24 V across 13 Ω, 48 V across 9 Ω, 230 V across 34 Ω, 110 V across 18 Ω. Which draws the smallest current? · 3 marks
- In a Kigali district office four loads are measured: 110 V across 24 Ω, 400 V across 73 Ω, 400 V across 42 Ω, 24 V across 54 Ω. Which draws the largest current? · 3 marks
- In a Kigali district office four loads are measured: 48 V across 17 Ω, 110 V across 54 Ω, 230 V across 41 Ω, 400 V across 5 Ω. Which dissipates the most power? · 3 marks
- In a sector office network four loads are measured: 230 V across 89 Ω, 110 V across 114 Ω, 400 V across 58 Ω, 48 V across 8 Ω. Which draws the smallest current? · 3 marks
- In a school computer lab four loads are measured: 230 V across 106 Ω, 230 V across 112 Ω, 12 V across 42 Ω, 24 V across 57 Ω. Which dissipates the most power? · 3 marks
- In a health-centre server room four loads are measured: 24 V across 44 Ω, 24 V across 48 Ω, 230 V across 92 Ω, 110 V across 53 Ω. Which dissipates the least power? · 3 marks
- In a TVET training workshop four loads are measured: 230 V across 59 Ω, 24 V across 36 Ω, 400 V across 76 Ω, 230 V across 11 Ω. Which dissipates the most power? · 3 marks
- In a school computer lab four loads are measured: 110 V across 39 Ω, 400 V across 84 Ω, 230 V across 74 Ω, 230 V across 20 Ω. Which draws the largest current? · 3 marks
- In a sector office network four loads are measured: 110 V across 75 Ω, 24 V across 32 Ω, 24 V across 105 Ω, 110 V across 73 Ω. Which draws the largest current? · 3 marks
- During a workshop assessment, the reported condition is: One branch of a parallel lighting circuit is open while the other branches remain connected to the supply. What behavior should the technician expect? · 3 marks
- During a workshop assessment, the reported condition is: Measured voltage rises and drops around a closed DC loop do not sum to approximately zero. What should be suspected first? · 1 mark
- During a workshop assessment, the reported condition is: Current measurements at a junction show 4 A entering but only 2.5 A accounted for in the measured outgoing branches. What is the best next step? · 3 marks
- During a workshop assessment, the reported condition is: A replacement fuse opens immediately each time the circuit is energized. What action is most appropriate? · 1 mark
- During a workshop assessment, the reported condition is: A circuit breaker trips only after a motor has operated under heavy mechanical load for several minutes. Which cause is most plausible? · 3 marks
- During a workshop assessment, the reported condition is: Residual-current protection trips when a damaged appliance is connected, but the branch overcurrent breaker does not trip. What does this pattern suggest? · 1 mark
- During a workshop assessment, the reported condition is: A 24 V control supply measures correctly with no load but falls to 15 V when a solenoid is energized. What should be investigated? · 3 marks
- During a workshop assessment, the reported condition is: A terminal is visibly discolored and much hotter than adjacent terminals while carrying normal circuit current. What is the most likely explanation? · 1 mark
- During a workshop assessment, the reported condition is: A three-phase motor's measured current is above its nameplate value while the driven machine is mechanically jammed. What should be addressed first? · 3 marks
- During a workshop assessment, the reported condition is: A technician must work on a DC bus containing large capacitors after the supply is isolated. What additional precaution is required? · 1 mark
- During a workshop assessment, the reported condition is: A relay coil is switched off and a large voltage spike appears across the control transistor. Which component action best limits the inductive transient in a DC coil circuit? · 3 marks
- During a workshop assessment, the reported condition is: A transformer has the expected primary voltage, but its secondary voltage is lower than the turns ratio predicts even with the load disconnected. What should be checked next? · 1 mark
- During a workshop assessment, the reported condition is: An industrial load draws substantial current, but a power meter shows real power much lower than apparent power. What does this indicate? · 3 marks
- During a workshop assessment, the reported condition is: One phase current of a running three-phase motor is nearly zero while the other two phase currents are abnormally high. Which fault is most likely? · 1 mark
- During a workshop assessment, the reported condition is: A newly connected three-phase motor rotates opposite the required direction. What is the standard correction after safe isolation? · 3 marks
- During a workshop assessment, the reported condition is: An insulation-resistance test is planned on electronic equipment containing sensitive control modules. What preparation is appropriate? · 1 mark
- During a workshop assessment, the reported condition is: A continuity check is needed on a protective conductor. Under what condition should the resistance measurement be made? · 3 marks
- During a workshop assessment, the reported condition is: A variable-frequency drive output is being checked with a basic average-responding meter, and the reading appears unstable. What tool choice is more appropriate? · 1 mark
- During a workshop assessment, the reported condition is: A current transformer's primary conductor is energized while its secondary circuit is open. Why is this dangerous? · 3 marks
- During routine technical work, which statement about verification of absence of voltage should guide the technician? · 3 marks
- An RC circuit has R = 137 Ω and C = 14 µF. What is its time constant, τ? · 1 mark
- Which statement about Kirchhoff's current law is correct? · 1 mark
- On a four-band resistor, what digit does a brown band represent? · 1 mark
- On a resistor, what digit does a black band represent? · 1 mark
- A 17 Ω resistor carries 0.2 A. What voltage is across it? · 1 mark
- A 16 Ω load is connected to 3.2 V. What current flows? · 1 mark
- A circuit has 6.3 V across it and draws 0.3 A. What is its resistance? · 1 mark
- Resistors 8 Ω, 17 Ω, and 26 Ω are in series. What is the total resistance? · 1 mark
- Resistors 15 Ω and 24 Ω are connected in parallel. What is the equivalent resistance? · 1 mark