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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-unit dishwasher is supplied by its own 120-volt branch circuit. Which statement describes the ground-fault protection the Code requires for that outlet?

  • Ground-fault circuit-interrupter protection is required whether the appliance is hardwired or cord-and-plug connected
  • BGround-fault circuit-interrupter protection is required only where the appliance is connected with a cord and attachment plug

    The connection method is not the trigger. Wiring the appliance directly instead of plugging it in leaves the outlet in place and the requirement along with it.

  • CNo ground-fault protection is required, because a hardwired supply point is not a receptacle outlet

    An outlet is any point where current is taken to supply utilization equipment, so a hardwired connection is an outlet. Protection is required whether or not a receptacle is present.

  • DGround-fault protection is required only where the appliance sits within 6 feet of the edge of the sink

    Proximity to a sink triggers protection for receptacles in certain locations, but the appliance rule applies to the listed appliances wherever they sit in the dwelling unit.

Why A is correct

The appliance provisions were written because dishwashers, disposals, and similar equipment sit in wet cabinets where a failing heating element or a chafed lead can energize the frame. Writing the rule around the outlet rather than around a receptacle closes the loophole that hardwiring used to create, so the protection follows the appliance either way.

What this question is testing

This item tests whether you know that ground-fault protection requirements extend to outlets supplying specific appliances, not just to receptacles, and whether you recognize that the rule is independent of location within the room.

On the job

This is one of the most version-sensitive corners of the Code, and it is a frequent source of arguments on remodels. Practically, it means the dishwasher circuit gets a ground-fault breaker, and it means you should warn the homeowner that a nuisance trip on an aging appliance is now a service call rather than an invisible slow leak to ground. Some appliance leakage currents are high enough that a failing unit trips the device immediately after installation.

Memory technique

The rule follows the appliance, not the plug.

Exam tip

Read the ground-fault section subdivision by subdivision. Dwelling receptacles, nondwelling receptacles, boat hoists, and specific appliances are separate lists.

Where to look it up

Ground-fault protection for personnel is early in Article 210, split into subdivisions by occupancy and by the kind of outlet. The appliance list is version sensitive, so confirm it in the edition your state has adopted.

4. A set of paralleled feeder conductors has a total allowable ampacity of 1,140 amperes after every correction and adjustment. The load is noncontinuous, the conductors supply no receptacles, and the standard device ratings bracketing that value are 1,000 and 1,200 amperes. What is the largest overcurrent device permitted to protect these conductors?

  • A1,200 amperes, using the next higher standard rating

    Rounding up is only permitted for devices of 800 amperes or less. Applying it here would leave the conductors protected at a value above their ampacity.

  • B1,140 amperes

    This figure is the conductor ampacity, not a standard device rating. Overcurrent devices are selected from the standard ratings the Code lists.

  • C800 amperes

    Eight hundred amperes is the threshold where the rule changes, not the answer. Choosing it throws away several hundred amperes of usable capacity.

  • 1,000 amperes

Why D is correct

Two rules cover conductor protection and the boundary between them is 800 amperes. At or below that value you may round up to the next standard rating. Above it, the conductor must carry at least as much as the device is rated, so you round down. Recognizing which side of the boundary a problem sits on is the entire skill being tested.

What this question is testing

This item tests whether you know the 800 ampere boundary in the conductor protection rules and whether you round the correct direction on each side of it.

On the job

This shows up on service and main switchgear sizing, where every 100 amperes of frame size is real money and where a design that rounds the wrong way either fails inspection or wastes copper. The practical move is to size the conductors so their ampacity lands at or above a standard rating rather than just below one, which usually means one more parallel set or one size larger conductor. Catching it at design is far cheaper than discovering it at energization.

Memory technique

Under eight hundred you may round up; over eight hundred the wire must carry the whole device.

Exam tip

Ask whether the device is above or below 800 amperes before you decide whether to round up or down. That single question decides these problems.

Where to look it up

Protection of conductors is at the front of Article 240, with the next-higher-rating allowance and the above-800-ampere rule in consecutive subdivisions.

5. A new one-family dwelling has an attached garage. What branch circuit does the Code require for the 125-volt receptacle outlets in that garage?

  • AAny existing 15- or 20-ampere general-purpose circuit that already serves the rooms next to the garage

    Sharing a general-purpose circuit with adjacent rooms is exactly what this rule was written to stop. A compressor or a shop vacuum then trips a circuit feeding bedrooms.

  • BA 20-ampere circuit that is shared with the required laundry receptacle outlet elsewhere in the dwelling

    The laundry circuit has its own dedication rule and may not take on garage receptacles. Combining them violates both provisions at once.

  • At least one 20-ampere circuit with no other outlets except readily accessible outdoor receptacles
  • DAt least one 20-ampere circuit that is also permitted to supply all of the lighting outlets in the garage

    Garage lighting is another outlet on the circuit. Putting lights on it means losing the light when a tool trips the breaker, which is the situation the dedication prevents.

Why C is correct

The rule creates a fourth dedicated circuit alongside the two small-appliance circuits and the laundry circuit. Its purpose is to keep the tool and vehicle loads in a garage off circuits that also feed living space. The only outlets allowed to share it are readily accessible outdoor receptacles, which is a deliberate allowance so one circuit can serve the garage and the exterior receptacles near it.

What this question is testing

The item tests recall of the dwelling dedicated-circuit list and the specific limit on what else that circuit may supply, which is the part candidates most often get wrong.

On the job

Panel schedules get drawn early and this circuit is the one most often left out on a residential job, because the garage receptacles look like ordinary general-purpose outlets. The rough-in inspector catches it, and the fix is a new home run through framing that is already insulated. Adding one dedicated 20-ampere circuit at layout costs a breaker and a cable. It also solves the real complaint that follows every garage: a shop tool killing the lights.

Memory technique

The garage gets its own twenty, and only the outdoor receptacles get to ride along.

Exam tip

Learn the dwelling dedicated circuits as a set: two small appliance, one laundry, one bathroom, one garage.

Where to look it up

Look in the branch circuits article, in the section on branch circuits required for specific occupancies, under dwelling units.

6. A communications provider proposes attaching an aerial drop to the same service mast that supports the electric service-drop conductors. How does the Code treat that?

  • AIt is permitted where the attachment is at least 12 inches below the electric service conductors

    Clearance below the electric conductors is a separate concern and does not create permission. The restriction is on what may be attached at all.

  • BIt is permitted where the mast is trade size 2 rigid metal conduit or larger and is guyed

    Mast size and guying address strength, which is the other half of the rule. Even a heavily guyed mast may not carry a communications drop.

  • 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

    Bonding a communications system to the intersystem bonding termination is required for other reasons and has nothing to do with mechanical attachment to the mast.

Why C is correct

The mast rule has two parts: the mast must be strong enough for the load imposed by the service drop, including any guying required, and nothing other than power service-drop or overhead service conductors may be attached to it. The second part is the one that answers this question, and it does not depend on the mast size or on where the attachment lands.

What this question is testing

The item tests whether the candidate knows a narrow, absolute restriction and can separate it from mechanical strength requirements and from grounding rules that also mention the mast area.

On the job

This argument happens on the roof, with two crews on site. The communications installer wants the mast because it is the only solid point on that gable, and the homeowner does not care who wins. The correct answer is a separate attachment point on the structure, which the communications article addresses. Masts that end up carrying two drops eventually pull out of the roof, and the electrical contractor owns the resulting leak and the reinstallation.

Memory technique

The mast belongs to the power drop and nothing else.

Exam tip

The service mast rule is short and absolute. Read the whole section, since strength and attachment are two different requirements in it.

Where to look it up

Look in the services part covering overhead service conductor installation, at the section on service masts used as supports.

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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