Branch Circuits, Feeders & Services — Electrician Practice Questions

75 questions · 16% of the Electrician exam

Worked questions

1. A feeder supplies a 65-ampere continuous load plus a 40-ampere noncontinuous load. Before any temperature correction or conductor bundling adjustment, what minimum ampacity must the feeder conductors have?

A105 amperes
One hundred five amperes is the simple sum of 65 and 40 with no continuous factor applied. It undersizes the conductors for the all-day portion of the load.
121.25 amperes
C131.25 amperes
One hundred thirty-one and a quarter amperes results from multiplying the entire 105-ampere load by 1.25. The noncontinuous portion does not get that factor.
D150 amperes
One hundred fifty amperes is a standard device rating and a common conductor size, but it is well above the calculated minimum and does not follow from the numbers given.

Why B is correct

Splitting the load and multiplying only the continuous portion gives 81.25 plus 40, or 121.25 amperes. The noncontinuous portion is always taken at 100 percent. That 121.25-ampere figure is the number you carry into the conductor ampacity table and into the overcurrent device selection, before any ambient correction or bundling adjustment is applied.

What this question is testing

Whether you correctly separate continuous from noncontinuous load before applying the multiplier, which is the defining skill for all feeder and service sizing.

On the job

The next step in the field is choosing a conductor whose table ampacity meets 121.25 amperes in the temperature column matching your terminations. A 1 AWG copper conductor at 75 degrees carries 130 amperes and covers it. Then the overcurrent device is sized to the same 121.25-ampere minimum, giving a 125-ampere device. Skipping the split calculation is how undersized shop feeders end up running warm.

Memory technique

Continuous gets the bonus, noncontinuous rides at face value.

Exam tip

Write the two loads on separate lines. Multiply only the continuous line by 1.25, then add.

Where to look it up

Section 215.2(A)(1) for feeder conductor sizing and 215.3 for the feeder overcurrent device. The branch-circuit equivalents are in Article 210.

2. A 120/240-volt, single-phase feeder has a calculated maximum unbalanced load on the grounded conductor of 260 A, with no nonlinear loads present. What minimum ampacity is required for that feeder neutral?

A182 amperes
One hundred eighty-two amperes results from applying the 70 percent factor to the entire 260-ampere unbalanced load. The reduction applies only to the excess above 200 amperes.
B200 amperes
Two hundred amperes treats 200 as a hard cap on the neutral. The rule reduces the excess, it does not eliminate it.
242 amperes
D260 amperes
Two hundred sixty amperes ignores the demand factor entirely. It is a safe but oversized answer and not the calculated minimum.

Why C is correct

Only the portion above 200 amperes gets the reduction. Two hundred at full value plus 42 from the reduced excess gives 242 amperes. The demand factor applies only to a three-wire single-phase or comparable system with no nonlinear load content, and the resulting neutral still may not be smaller than the minimum size required for the feeder.

What this question is testing

Whether you apply a stepped demand factor to only the qualifying portion of a load, a pattern that repeats throughout the load calculation article.

On the job

The reduction exists because on a large mixed load, the odds of the two ungrounded legs being severely unbalanced at the same moment drop as the load grows. Two important limits: no reduction is permitted for the portion of the load that is nonlinear on a four-wire wye system, because harmonic currents add in the neutral rather than cancel, and range and dryer neutral loads are handled by their own provisions.

Memory technique

First two hundred at full price, the rest at seventy percent off the top.

Exam tip

Everything through 200 amperes stays whole. Only what is above 200 gets multiplied by 0.70.

Where to look it up

Section 220.61 covers feeder and service neutral load, with the demand factor and the nonlinear-load restriction in separate subdivisions. Section 215.2(A) sets the floor size for a feeder grounded conductor.

3. A dwelling dishwasher is rated 120 volts to ground and 15 amperes on a single-phase circuit. Under 2023 NEC 210.8(D), which statement applies?

GFCI protection is required whether hardwired or connected by cord and plug
BGFCI protection is required only for cord-and-plug connection
CHardwiring eliminates the protection requirement
DProtection is required only within 6 feet of a sink

Where to look it up

https://captaincode2023.leviton.com/node/308

Why A is correct

Dishwashers are included, and this appliance falls within the provision’s voltage and current limits. Protection applies to the supplying branch circuit or outlet; hardwiring and distance from the sink do not remove it. This provision does not mandate a circuit-breaker implementation as the only possible method. Source: https://captaincode2023.leviton.com/node/308

4. An ordinary feeder has 1,140 A allowable conductor ampacity after all adjustments and a 950 A noncontinuous load. No special conductor-protection exception applies. Select a fixed, nonadjustable standard-rated overcurrent device; the standard ratings bracketing 1,140 A are 1,000 A and 1,200 A. Under 2023 NEC 240.4(C), what is the largest qualifying standard rating?

A1,200 A, by rounding up
B1,140 A, treating conductor ampacity as a standard device rating
C800 A
1,000 A

Where to look it up

https://docinfofiles.nfpa.org/files/AboutTheCodes/70/70_A2025_NEC_P10_FD_PIResponses.pdf

Why D is correct

For a device rated above 800 A, the protected conductors must have ampacity at least equal to the device rating. Thus 1,200 A exceeds the available 1,140 A ampacity, while 1,000 A does not and also covers the stated 950 A load. The question expressly selects a fixed standard rating; it does not rule out every possible adjustable or nonstandard design. Source: unchanged 2023 baseline 240.4(C), NFPA Public Input 705, PDF page 434 (printed 321). https://docinfofiles.nfpa.org/files/AboutTheCodes/70/70_A2025_NEC_P10_FD_PIResponses.pdf

5. A new dwelling has an attached two-bay garage. Under 2023 NEC 210.11(C)(4), which circuit arrangement is required for the receptacles required by 210.52(G)(1)?

AAn adjacent bedroom’s existing 15-ampere circuit
BThe required laundry circuit
At least one 120-volt, 20-ampere garage circuit; outdoor receptacles may also be supplied
DAny 15-ampere circuit, provided all garage lighting shares it

Where to look it up

https://captaincode2023.leviton.com/node/310

Why C is correct

The required garage receptacles need the stated 20-ampere circuit. The outdoor-receptacle exception applies. The separate exception allowing other equipment in a single-bay garage does not apply to this two-bay case. Additional circuits of at least 15 amperes may serve garage receptacles beyond those required by 210.52(G)(1); that permission does not replace the required circuit. Source: https://captaincode2023.leviton.com/node/310

6. A communications provider proposes attaching an aerial drop to the service mast that supports a house’s electric service-drop conductors. Under 2023 NEC 230.28, how is this proposal treated?

AIt is permitted where the attachment is at least 12 inches below the electric service conductors
BIt is permitted where the mast is trade size 2 rigid metal conduit or larger and is guyed
It is not permitted; only power service-drop or overhead service conductors may be attached to a service mast
DIt is permitted where the communications drop is bonded to the intersystem bonding termination at the meter enclosure

Where to look it up

https://dos.ny.gov/nys-residential-code-noa-7242025

Why C is correct

Only power service-drop or overhead service conductors may be attached to a service mast. Additional clearance, a stronger or guyed mast, or communications bonding does not authorize the proposed attachment. Mechanical strength is a separate requirement. The rule does not establish that every improper attachment inevitably causes a roof leak or determines who is legally liable. Source: 2023 NEC 230.28, extracted at 2024 IRC E3604.5-.5.2, reproduced in the official 2025 RCNYS, based on 2024 IRC with electrical provisions extracted from 2023 NEC. https://dos.ny.gov/nys-residential-code-noa-7242025

7. A 120-volt branch circuit protected at 20 amperes serves a steady 16-ampere load 75 feet from the panel. The conductors are 12 AWG solid uncoated copper, which Chapter 9, Table 8 lists at 1.93 ohms per 1,000 feet. Treating the circuit as a simple resistance and remembering that the current travels out and back, what is the approximate voltage drop?

AAbout 2.3 volts
This uses the 75-foot one-way length. The current has to return on the second conductor, so the resistance in the loop is that of 150 feet of wire.
About 4.6 volts
CAbout 9.3 volts
This uses 300 feet, doubling the run and then doubling it again for the return path. The out-and-back doubling happens once.
DAbout 5.8 volts
This uses the 20-ampere rating of the overcurrent device instead of the 16-ampere load. Drop depends on the current actually flowing, not on the size of the breaker protecting the circuit.

Why B is correct

Total conductor length is 75 feet out plus 75 feet back, or 150 feet. Resistance is 1.93 x (150 / 1,000) = 0.29 ohm. Ohm's law then gives 16 x 0.29 = 4.63 volts, about 3.9 percent of 120 volts. Working from table resistance is the same calculation as the constant method; only the way the conductor property is expressed changes.

What this question is testing

Tests whether you can build the total loop resistance from a per-1,000-foot figure and apply Ohm's law to it, and whether you use the actual load current rather than the overcurrent device rating when computing drop.

On the job

Manufacturers publish conductor resistance rather than a drop constant, and so does the Code's own conductor properties table, so this is the method you fall back on when a problem or a submittal hands you ohms per 1,000 feet. It also makes the physics visible: the circuit is nothing but a load in series with a length of wire, and the wire takes its share of the voltage in proportion to its resistance.

Memory technique

Out and back: the loop is always twice the run.

Exam tip

Ohms per 1,000 feet times the total feet of conductor in the loop, divided by 1,000, then multiply by the load current.

Where to look it up

Chapter 9, Table 8 lists dc resistance per 1,000 feet separately for solid and stranded, coated and uncoated conductors.

68 more in the bank

Answers and explanations for these are in the app.

In Code terminology, which conductors make up a branch circuit in a typical dwelling panelboard installation?
A 100-ampere circuit runs from the main service panel of a house to a subpanel in a detached shop. What is the correct classification for those conductors?
At minimum, how many small-appliance branch circuits must be provided to supply the receptacle outlets in the kitchen, pantry, breakfast room, and dining room of a dwelling unit?
A dwelling unit requires a dedicated 20-ampere laundry branch circuit. Which loads is that circuit permitted to supply?
A 20-ampere branch circuit serves the receptacle outlets in a dwelling-unit bathroom. Under what condition may that same circuit also supply the exhaust fan and vanity lighting?
Measured along the floor line of usable wall space in a dwelling living room, what is the greatest distance any point may be from a receptacle outlet?
Along a straight run of kitchen countertop with no sink or range breaking it up, what is the greatest horizontal distance permitted from any point on that counter to the nearest receptacle outlet serving it?
What is the minimum ampere rating permitted for the service disconnecting means of a new one-family dwelling supplied by a 120/240-volt, three-wire service?
A 125-volt receptacle is installed in a dwelling wet bar area, 4 feet from the top inside edge of the bar sink bowl. What protection does the Code require for that receptacle?
Which of these 125-volt, 15-ampere receptacle locations in a single-family dwelling requires ground-fault circuit-interrupter protection for personnel?
Which dwelling-unit area is among those where 120-volt, 15- and 20-ampere branch circuits supplying outlets must have arc-fault circuit-interrupter protection?
Which of the following values appears in the Code list of standard ampere ratings for fuses and inverse-time circuit breakers?
A set of feeder conductors has an allowable ampacity that falls between two standard overcurrent device ratings. Under what conditions may the next higher standard device rating be used to protect them?
Absent any of the specific exceptions in the Code, what is the maximum overcurrent device rating permitted to protect a 12 AWG copper branch-circuit conductor?
Tap conductors are run 22 feet from a 300-ampere feeder and terminate in a single overcurrent device in a downstream panelboard. What minimum ampacity must those tap conductors have?
For a single set of service-entrance conductors supplying a building, what is the maximum number of service disconnecting means permitted?
Where must the service disconnecting means for a building be installed relative to the service-entrance conductors?
You are setting a 120/240-volt, 200-ampere panelboard that will be examined and serviced while energized. What is the minimum required depth of clear working space in front of that equipment?
A multiwire branch circuit supplies two 20-ampere kitchen circuits from a shared neutral conductor. What does the Code require of the ungrounded conductors at the panelboard?
Which equipment is specifically permitted by the Code to be connected on the supply side of the service disconnecting means?
A 20-ampere branch circuit will supply a lighting load that operates continuously for more than three hours at a time. What is the maximum continuous load this circuit is permitted to carry?
A branch circuit supplies a 44-ampere continuous load and nothing else. What is the smallest standard-rated overcurrent device that may protect this circuit?
Three current-carrying 6 AWG copper THHN conductors are installed in a raceway in a 30-degree Celsius ambient. The equipment at both ends is listed for 75-degree Celsius terminations. Which ampacity governs this conductor run?
A 4 AWG copper feeder terminated on lugs listed for 75 degrees Celsius supplies an 82-ampere noncontinuous load, with no correction or adjustment factors required. What is the largest standard overcurrent device permitted to protect this feeder?
A restaurant kitchen contains 125-volt, 20-ampere receptacles mounted on the walls well away from any countertop or sink. What ground-fault protection does the Code require for those receptacles?
A ground-fault circuit interrupter protects a group of receptacles in a commercial garage. Where does the Code require that device to be installed?
An existing 15-ampere branch circuit supplying bedroom receptacles in a dwelling is extended to add two new outlets. What does the Code require once that work is complete?
An office building is being wired and the plans show conference rooms of 400, 800 and 1,400 square feet. The Code sets a prescriptive minimum for receptacle outlets in meeting rooms, aimed at 125-volt, 15- and 20-ampere nonlocking receptacles. Which of those rooms fall within the scope of that requirement?
A dwelling-unit bathroom has one basin set into a vanity. Where does the Code require a receptacle outlet to be installed?
A kitchen has several separate countertop spaces broken up by a range and a sink. Which of those spaces requires a receptacle outlet of its own?
Receptacle outlets are required along the wall space of a dwelling-unit room. Which description matches what the Code counts as wall space for that purpose?
A dwelling-unit living room has a receptacle installed in the floor near a wall. Under what condition may that floor receptacle be counted toward the required receptacle outlets for that wall space?
A retail store has a show window running along the sidewalk. What receptacle outlet requirement applies to that window?
A contractor proposes installing the panelboard for a dwelling unit inside the bathroom, on the wall opposite the tub. How does the Code treat overcurrent devices in that location?
A panelboard is being mounted in a utility room of a commercial building. What does the Code require about the mounting height of the overcurrent devices inside it?
A multiwire branch circuit leaves a panelboard on its way to a kitchen. What does the Code require of its ungrounded and grounded conductors at the point where the circuit originates?
Receptacles on a multiwire branch circuit have been wired so that the grounded conductor runs into one terminal of each device and out the other. What does the Code require instead?
Overhead service-drop conductors are attached to a residence and terminate at a service head on the mast. Where does the Code require that service head to be located?
Open overhead service conductors run along the side of a two-story dwelling that has windows designed to be opened. What clearance does the Code require between those conductors and the openings?
A single commercial building is to be supplied with electric power. What does the Code state as the general rule for the number of services to that building?
Tap conductors leave a 1,200-ampere feeder and run about 60 feet along the exterior of a building before entering it. Under which set of conditions does the Code permit tap conductors of unlimited length?
A design requires that the overcurrent devices in a system be selectively coordinated. What does that term describe?
A branch circuit is wired with 10 AWG copper conductors but is protected by a 20-ampere overcurrent device. How is the rating of that branch circuit determined?
A commercial building has three service disconnecting means grouped at a single location. What does the Code require regarding identification of that equipment?
A receptacle outlet is installed specifically to supply a particular piece of appliance equipment, such as a room air conditioner. Where does the Code require that receptacle to be placed?
Conductors are tapped from a larger feeder to supply a small panelboard. Where does the Code generally require the overcurrent protection for those tapped conductors to be located?
A 480-volt, three-phase feeder carries 40 amperes over a one-way distance of 300 feet, and voltage drop is to be held to 3 percent. Use the relationship in which voltage drop equals 1.732 times K times current times one-way distance divided by circular mils, with K taken as 12.9 for copper. The circular mil areas are 10,380, 16,510, 26,240, and 41,740 for 10, 8, 6, and 4 AWG respectively. What is the smallest copper conductor that holds the drop within the limit?
In an office building, general-use receptacle outlets are computed at 180 volt-amperes each and the load is not continuous. What is the greatest number of such outlets that may be placed on one 20-ampere, 120-volt branch circuit?
A 30-foot length of multioutlet assembly is installed in an office where the appliances plugged into it are unlikely to be used at the same time. Under that condition the Code assigns 180 volt-amperes for each 5 feet or fraction of the assembly. What load must be included for that assembly?
A 480-volt, three-phase, three-wire feeder is installed as two parallel sets of 3/0 AWG copper THWN-2, with all six conductors in a single raceway at an ambient of 30 degrees Celsius. The table gives this conductor 165, 200, and 225 amperes in the 60, 75, and 90 degree Celsius columns respectively. The adjustment factor for six current-carrying conductors is 0.80, and terminations are rated 75 degrees Celsius. What is the allowable ampacity of the paralleled feeder?
A bedroom in a dwelling unit is shown on the plans with no ceiling luminaire. What does the Code require for lighting in that room?
An interior stairway in a dwelling connects two floor levels with eight steps between them, and lighting outlets are installed in the stairway. What switching does the Code require?
A 20-ampere branch circuit in a dwelling supplies lighting outlets and receptacle outlets, and a piece of utilization equipment fastened in place is to be added to the same circuit. What limit applies to the rating of that fastened equipment?
An installer proposes pulling a control conductor for a utility load management relay through the same raceway that contains the service-entrance conductors. How does the Code treat that?
A set of ungrounded service-entrance conductors has an allowable ampacity of 285 amperes after all corrections. What does the Code permit for the rating of the overcurrent device protecting them?
Under the general rule, how many sets of service-entrance conductors may a single service drop or service lateral supply?
A detached shop on the same property is supplied from the panelboard in the dwelling. Under the general rule, how many feeders or branch circuits may supply that structure?
A building is supplied by a solidly grounded wye service at 480Y/277 volts through a single service disconnecting means rated 1200 amperes. What does the Code require for that disconnect?
An installer proposes landing two 100-ampere fuses side by side on the same set of terminals so that the pair together carries 200 amperes. How does the Code treat overcurrent devices connected in parallel?
Under the 2023 Code, which statement describes the ground-fault circuit-interrupter requirement that applies to outdoor outlets at a dwelling unit?
A separate building is supplied by its own service consisting of exactly two branch circuits. What is the minimum ampere rating permitted for the service disconnecting means?
A 480Y/277-volt, three-phase branch circuit supplies a lighting load that draws 44 amperes on each phase and operates continuously for more than three hours at a time. Before any temperature correction or conductor adjustment, what minimum ampacity must the branch-circuit conductors have?
Service-entrance conductors must be lengthened during a meter relocation. How does the Code treat splicing those conductors?
Circuit breakers in a panelboard are mounted so that their handles operate vertically rather than rotationally or horizontally. What does the Code require about handle position?
A circuit breaker is marked with a slash voltage rating of 120/240 volts. On which systems does the Code permit that breaker to be applied?
A panelboard is going to be used as the service equipment at a new one-family dwelling. What marking does the Code require on that equipment?
A fusible switch serves as the service disconnecting means, and the fuses are proposed to be installed in a separate enclosure about 20 feet away from that switch. How does the Code treat that arrangement?
A commercial building is to have four service disconnecting means. Under the current Code, how may those four disconnects be arranged?

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Branch Circuits, Feeders & Services — Electrician Practice Questions

Worked questions

1. A feeder supplies a 65-ampere continuous load plus a 40-ampere noncontinuous load. Before any temperature correction or conductor bundling adjustment, what minimum ampacity must the feeder conductors have?

2. A 120/240-volt, single-phase feeder has a calculated maximum unbalanced load on the grounded conductor of 260 A, with no nonlinear loads present. What minimum ampacity is required for that feeder neutral?

3. A dwelling dishwasher is rated 120 volts to ground and 15 amperes on a single-phase circuit. Under 2023 NEC 210.8(D), which statement applies?

5. A new dwelling has an attached two-bay garage. Under 2023 NEC 210.11(C)(4), which circuit arrangement is required for the receptacles required by 210.52(G)(1)?

6. A communications provider proposes attaching an aerial drop to the service mast that supports a house’s electric service-drop conductors. Under 2023 NEC 230.28, how is this proposal treated?

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