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BASIC NEC 2023

Voltage Drop Fundamentals Practice Test

Free online voltage drop fundamentals practice test. 25 basic electrical questions on why voltage drop happens, the voltage drop formula, and calculating percentage voltage drop. Good for electrician exam prep.

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Voltage Drop Basics Voltage Drop Factors Voltage Drop Formula Voltage Drop Calculations Voltage Drop Guidelines Voltage Drop Effects

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Every real conductor has some resistance, and that resistance causes a small amount of voltage to be "lost" along the way — this is voltage drop. It matters because equipment on the far end of a long circuit may not get the full voltage it needs: motors can overheat, lights can dim, and electronics can malfunction. This quiz covers the underlying theory and basic math of voltage drop, at the conceptual/formula level, before you ever open a specific code table.

25

Questions

38 min

Time

75%

Pass

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Voltage Drop Fundamentals Practice Test — Question List

Question 1: "Voltage drop" refers to:

The loss of voltage along a conductor caused by the conductor's own resistance
A type of short circuit
The voltage rating printed on a breaker
A deliberate feature that has no downside

Question 2: Voltage drop happens because, fundamentally:

Every real conductor has some resistance, and Ohm's Law (V = I x R) means current flowing through that resistance produces a voltage across it
Conductors have zero resistance, so voltage drop is purely theoretical
It only happens in conductors made of glass
It happens only when a circuit breaker is open

Question 3: All else being equal, a LONGER conductor run will have:

More voltage drop
Less voltage drop
Exactly zero voltage drop
No relationship to voltage drop at all

Question 4: All else being equal, using a LARGER (thicker) conductor for the same run will result in:

Less voltage drop
More voltage drop
No change in voltage drop whatsoever
The circuit will stop working entirely

Question 5: All else being equal, if the current flowing through a conductor INCREASES, the voltage drop will:

Increase
Decrease
Stay exactly the same
Become negative

Question 6: Excessive voltage drop can cause equipment problems such as:

Motors running hot and inefficiently, lights dimming, and sensitive electronics malfunctioning
No effect on any equipment under any circumstances
Equipment always runs better with lower voltage
It only affects the color of light bulbs

Question 7: The basic single-phase voltage drop formula is:

VD = 2 x I x R x L / 1000
VD = I / R
VD = I + R + L
VD = R / (I x L)

Question 8: In the single-phase voltage drop formula, why does the distance get multiplied by 2?

Because current has to travel out to the load AND back to the source, so the total circuit path is twice the one-way distance
It is an arbitrary safety margin with no physical reason
Because all conductors are always sold in pairs
Because voltage always doubles in every circuit

Question 9: A circuit carries 15 A over a one-way distance of 100 ft, using a conductor with a resistance of 2 ohms per 1,000 ft. What is the voltage drop?

3 V
6 V
30 V
60 V

Question 10: The formula for calculating PERCENTAGE voltage drop is:

%VD = (VD / source voltage) x 100
%VD = VD x source voltage
%VD = source voltage / VD
%VD = VD + source voltage

Question 11: Using the 6 V drop found earlier on a 120 V circuit, what is the percentage voltage drop?

0.5%
5%
20%
50%

Question 12: As a widely used general engineering guideline (not a strict legal requirement), branch-circuit voltage drop is commonly recommended to stay under about:

3%
15%
25%
50%

Question 13: As a widely used general engineering guideline, the TOTAL voltage drop (feeder plus branch circuit combined) is commonly recommended to stay under about:

5%
1%
10%
20%

Question 14: As a conductor gets HOTTER, its resistance generally:

Increases
Decreases
Stays exactly the same
Drops to zero

Question 15: A motor supplied through a conductor with excessive voltage drop will often show which symptom?

It draws MORE current than normal while producing LESS torque, running hotter as a result
It draws less current and runs cooler than normal
There is no effect on a motor from voltage drop
The motor automatically increases its own voltage rating

Question 16: If a calculated voltage drop is higher than desired, the most common practical remedy (without changing the load or distance) is to:

Increase the conductor size to reduce its resistance
Decrease the conductor size
Add more distance to the run
Increase the current draw of the load

Question 17: A circuit carries 20 A over a one-way distance of 250 ft, using a conductor with a resistance of 1 ohm per 1,000 ft. What is the voltage drop?

5 V
10 V
50 V
100 V

Question 18: Using the 10 V drop from the previous example on a 240 V circuit, what is the approximate percentage voltage drop?

0.4%
4.2%
24%
42%

Question 19: For the same conductor size and length carrying the same current, which material generally produces LESS voltage drop: copper or aluminum?

Copper
Aluminum
They produce identical voltage drop always
Neither material has any resistance

Question 20: A conductor that is correctly sized for AMPACITY (safe current-carrying capacity) is:

Not automatically guaranteed to have acceptable voltage drop -- these are two separate, independent checks
Automatically guaranteed to have zero voltage drop
The exact same thing as being sized for voltage drop
Irrelevant to voltage drop in every case

Question 21: All else being equal, SHORTENING a conductor run will result in:

Less voltage drop
More voltage drop
No change at all
The circuit will automatically fail

Question 22: Excessive voltage drop on a lighting circuit typically causes:

Noticeably dimmer lighting than expected, since the fixtures receive less than the full rated voltage
Brighter than normal lighting
No visible effect on lighting whatsoever
The lights will automatically switch to battery backup

Question 23: A circuit carries 10 A over a one-way distance of 50 ft, using a conductor with a resistance of 3 ohms per 1,000 ft. What is the voltage drop?

1.5 V
3 V
15 V
30 V

Question 24: True or false: voltage drop only occurs when there is a fault or wiring defect in a circuit.

False
True
Only true for aluminum conductors
Only true for DC circuits

Question 25: If BOTH the current AND the one-way distance of a circuit are doubled (with the same conductor size), how does the voltage drop change compared to the original?

It doubles (2 times larger)
It becomes 4 times larger
It stays exactly the same
It is cut in half

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)