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BASIC NEC 2023

Open/Short/Ground Fault Theory Practice Test

Free online open, short, and ground fault theory practice test. 25 basic electrical questions on fault symptoms, voltage and resistance testing, and troubleshooting series and parallel circuit faults. Good for electrician exam prep.

TOPICS COVERED

Open Circuit Definition Short Circuit Definition Ground Fault Definition Symptoms of an Open Circuit Symptoms of a Short Circuit Voltage Across an Open Point

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Three fault types show up again and again in troubleshooting. An open circuit is a broken path — no current flows, and a voltmeter across the break reads full source voltage. A short circuit is an unintended low-resistance path — current spikes way up (I = V/R, with R near zero), tripping the breaker fast. A ground fault is a specific kind of short: an unintended path to ground. In a SERIES circuit, one open point kills the whole circuit; in a PARALLEL circuit, an open only kills that one branch. Know your test readings: an ohmmeter reads near-infinite resistance at an open, and near-zero resistance across a short.

25

Questions

38 min

Time

75%

Pass

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Open/Short/Ground Fault Theory Practice Test — Question List

Question 1: An "open circuit" is best described as:

A broken path in a circuit that prevents any current from flowing
A path with extremely low resistance that allows excess current to flow
A perfectly normal, fully functioning circuit
A circuit with no source voltage connected by design

Question 2: A "short circuit" is best described as:

An unintended, low-resistance path that allows excessive current to flow
A broken path that prevents any current from flowing
A perfectly normal, fully functioning circuit
A circuit intentionally left disconnected

Question 3: A "ground fault" is best described as:

An unintended electrical connection between an energized conductor and ground
A planned, intentional grounding connection made during installation
A complete break in a circuit with no path at all
A normal condition present in every properly working circuit

Question 4: A telltale symptom of an open circuit is that the affected device:

Simply does not work at all, since no current can flow to it
Trips the breaker instantly with visible sparking
Runs hotter than normal while working perfectly fine
Runs faster than its rated speed

Question 5: A telltale symptom of a short circuit is that:

The circuit breaker trips or the fuse blows almost immediately, often with sparking
The affected device simply stops working with no other symptoms
Nothing changes at all — the circuit behaves completely normally
The circuit slowly loses voltage over several days

Question 6: When measuring voltage across an open switch or broken connection in an energized circuit, a voltmeter will typically read:

The full source voltage, since all of the voltage drop appears across the open point
Exactly zero volts, always
A random, unpredictable value with no relationship to the source
Twice the source voltage

Question 7: When measuring voltage across a good, closed connection carrying normal current, a voltmeter will typically read:

A very small voltage, close to zero, since a good connection has very little resistance
The full source voltage
A value that has nothing to do with the connection's condition
Always exactly half the source voltage

Question 8: Using an ohmmeter (on a de-energized circuit) to test for an open circuit, you would expect to see a reading of:

Infinite (or very high) resistance at the point of the break
Exactly zero ohms
A steady, moderate resistance reading
A reading that fluctuates randomly with no pattern

Question 9: Using an ohmmeter (on a de-energized circuit) to test for a short circuit, you would expect to see a reading of:

Very low (near zero) resistance between two points that should normally be isolated from each other
Infinite resistance between those two points
No reading of any kind is possible
A reading identical to a fully open circuit

Question 10: If an open circuit occurs anywhere in a SERIES circuit, the effect is that:

The entire circuit stops working, since there is only one path for current
Only the component nearest the source stops working
Nothing changes — series circuits are unaffected by open faults
The circuit current increases significantly

Question 11: If an open circuit occurs in one branch of a PARALLEL circuit, the effect is that:

Only that branch stops working; the other branches continue operating normally
The entire parallel circuit stops working immediately
All branches immediately short circuit
The source voltage drops to zero everywhere

Question 12: If a short circuit occurs across one component in a SERIES circuit, the most likely effect is that:

Current bypasses that component, and the circuit current increases significantly
The entire circuit immediately goes to zero current
Nothing changes — short circuits have no effect on series circuits
The circuit voltage doubles automatically

Question 13: The key distinction between a "ground fault" and a general "short circuit" is that a ground fault specifically involves:

An unintended path to ground/earth, while "short circuit" is a broader term that can also describe a fault between two energized conductors
Nothing — the two terms are always completely interchangeable in every case
A ground fault never involves any current flow at all
A short circuit can never involve a connection to ground

Question 14: A "line-to-line" short circuit differs from a "line-to-ground" fault in that a line-to-line short involves:

Two energized (hot) conductors coming into unintended contact with each other, rather than a hot conductor contacting ground
A conductor that is completely disconnected from the circuit
A perfectly normal, intended electrical connection
A condition that can never actually occur in practice

Question 15: During a ground fault on properly grounded equipment, fault current is intended to flow back to the source through the:

Equipment grounding conductor, providing a low-impedance path that trips the overcurrent device
Ungrounded (hot) conductor exclusively, with no other path involved
Air, with no conductor path needed at all
Nothing — ground faults never produce any current flow

Question 16: A short circuit produces very high current mainly because, according to Ohm's Law, extremely low resistance combined with the source voltage results in:

A very large calculated current (I = V / R, and R is nearly zero)
A very small calculated current, near zero
No current at all, regardless of the resistance value
A current value that has no relationship to resistance

Question 17: When a short circuit occurs, the overcurrent protective device (breaker or fuse) typically responds by:

Tripping or blowing very quickly, due to the very high current involved
Taking several hours to respond, regardless of current level
Never tripping under any short-circuit condition
Increasing its trip threshold automatically

Question 18: Unlike the fast response to a short circuit, an overcurrent protective device responds to a sustained OVERLOAD condition (moderately excessive current) by:

Tripping more slowly, based on a time-delay (thermal) characteristic that allows brief harmless overloads to pass
Tripping at exactly the same instantaneous speed as it does for a short circuit
Never tripping under any overload condition
Immediately doubling the circuit voltage

Question 19: Common causes of open circuits include:

A broken wire, a loose connection, a blown fuse, or a failed switch
Perfectly tight, well-maintained connections
A properly sized overcurrent device operating normally
Correctly installed insulation with no damage

Question 20: Common causes of short circuits include:

Damaged insulation, a pinched wire, water intrusion, or a foreign object bridging two conductors
Perfectly intact insulation with no damage of any kind
A properly torqued and tightened connection
Correctly sized conductors installed to specification

Question 21: A logical troubleshooting approach for locating a fault in a circuit is to:

Isolate and test sections of the circuit one at a time using voltage or continuity testing, narrowing down the fault location
Randomly replace parts until the circuit happens to work again
Avoid any testing and guess based on appearance alone
Increase the circuit voltage until the fault becomes visible

Question 22: In a series circuit with one open component, the voltage across each of the OTHER (still good) components will typically read:

Close to zero, because no current is flowing to create a voltage drop across them
The full source voltage across every single good component
A value that increases steadily over time
Exactly double the source voltage

Question 23: Beyond simply tripping a breaker, a short circuit can also pose serious dangers such as:

Arc flash, fire, and damage to equipment from the extreme current involved
No danger of any kind beyond the breaker tripping
A permanent, harmless reduction in circuit voltage
Improved circuit efficiency and lower energy costs

Question 24: If a ground fault occurs inside a properly grounded metal appliance housing, the equipment grounding conductor's role is to:

Provide a path for fault current back to the source, tripping the breaker before the housing can become a shock hazard
Increase the appliance's operating voltage
Prevent the appliance from ever being turned on
Convert the fault current into useful working power

Question 25: A technician measures a de-energized circuit with an ohmmeter. At one suspected fault location, resistance reads very high (nearly infinite). At another nearby location, resistance reads very low between two conductors that should be isolated. These two readings most likely indicate:

An open circuit at the first location and a short circuit at the second location — two separate, different faults
Both readings indicate the exact same type of fault
The meter must be broken, since two different readings are impossible
Neither reading has any diagnostic meaning

EXAM CARD BASIC

Questions25

Time limit38 min

Pass score75%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 (NFPA 70)