Residential Circuit Planning: Loads, Layout, and Protection

A helper pulls cable where the plan says. A mid-level electrician helps write the plan. That means knowing which circuits a house must have, how much each one can carry, where receptacles have to go, and what protection each room needs. Mistakes here cost more than mistakes anywhere else, because a missing circuit is found after the drywall is up. This work is done under a licensed electrician, who approves the layout and answers for it. Your job is to bring a plan that is already right.

What You Will Be Able to Do

• List the circuits a dwelling must have and pair each with the right wire and breaker.
• Check a circuit against the 80 percent and 50 percent limits.
• Lay out receptacles in a kitchen, bath, hallway and garage.
• Choose GFCI, AFCI or dual-function protection for each room.
• Plan a multiwire circuit and a detached-garage feeder safely.
• Say where the code edition or a local rule changes the answer.

Section numbers are from the National Electrical Code (NEC), mostly the 2023 edition. Many states enforce 2020 or 2023, some have moved to 2026, and cities add amendments. The edition adopted where the job sits is the one that counts, so confirm it before you plan.

Start With the Questions

Before you mark a stud, get these answers from the plans, the builder and your supervisor:

1. Which NEC edition and which local amendments apply?
2. Is the range, dryer and water heater electric or gas?
3. Is the heat electric, gas or a heat pump, and what are the nameplate numbers?
4. Is there an EV charger, hot tub, generator or solar now, or planned later?
5. What wiring method is allowed? Some cities do not allow NM cable.
6. Where does the panel go, and does it have clear working space?

The answers set the panel size and the number of spaces. A plan that ignores an electric range or an EV charger is a plan you will redo.

The Required Circuits

NEC 210.11(C) names circuits that a dwelling must have no matter how small it is.

The bathroom rule gives you a choice. One 20-amp circuit can feed the receptacles in several bathrooms. Or it can feed one bathroom's receptacles, lights and fan, but nothing outside that room.

Small-appliance circuits are for receptacles. Do not put the kitchen lights on them, and do not count a refrigerator as a reason to skip one. Dedicated loads such as a dishwasher, disposal, microwave and range get their own circuits as the appliance instructions and your plan require.

Pairing Wire and Breaker

For copper NM cable in a house, the pairings are fixed:

These come from the 60 degree C ampacity column for NM cable and the small-conductor limits in NEC 240.4(D). A longer run may need a bigger wire for voltage drop, but it never gets a bigger breaker because of that.

How Much a Circuit Can Carry

Two limits catch people out.

Continuous loads. A continuous load runs at its full current for three hours or more. Under 210.19 and 210.20, the circuit and breaker are sized at 125 percent of that load. Said the other way, a continuous load may use only 80 percent of the breaker. On a 20-amp circuit that is 16 amps. EV chargers, and many water heaters and electric heat loads, are treated this way.

Fastened-in-place equipment. Under 210.23, on a 15- or 20-amp circuit that also feeds other outlets, equipment fastened in place may not exceed 50 percent of the circuit rating. A single cord-and-plug load may not exceed 80 percent.

Worked Example: Can the Microwave Share?

A built-in microwave draws 13 amps and is fastened in place. Your plan puts it on a 20-amp circuit with two pantry receptacles.

1. The 50 percent limit on a 20-amp circuit is 10 amps.
2. The microwave draws 13 amps, which is over that limit.
3. Give the microwave its own 20-amp circuit.

The same microwave alone on a 20-amp circuit is fine, because no other outlets share it.

Worked Example: An EV Charger

A charger is set to draw 32 amps continuously.

1. 32 x 1.25 = 40 amps.
2. Use a 40-amp breaker and a wire good for at least 40 amps at the terminal rating, per the charger's instructions.

A 40-amp breaker with a 40-amp continuous load is a violation, even though the numbers look equal. The most that breaker can carry continuously is 32 amps.

Receptacle Layout

Ordinary Walls

NEC 210.52(A) is the 6-foot rule. No point along a wall may be more than 6 feet from a receptacle, measured along the floor line. That works out to a receptacle at least every 12 feet. Any wall 2 feet or wider counts. Fixed room dividers and railings count as walls. A doorway does not.

Kitchen Counters

Under 210.52(C), each wall counter space 12 inches or wider needs a receptacle, and no point along the wall line may be more than 24 inches from one. So receptacles along a counter may be no more than 4 feet apart. A sink or a range breaks the counter into separate spaces, so plan each space by itself.

Island and peninsula rules have changed in each recent edition, which is why you check first:

Other Rooms

Tamper-resistant (TR) receptacles are required throughout a dwelling. NEC 406.12 covers all 15- and 20-amp, 125- and 250-volt nonlocking receptacles, with narrow exceptions such as a receptacle more than 5-1/2 feet above the floor. A customer who finds them stiff does not get to opt out. Outdoors and in other wet or damp spots, use a weather-resistant type.

Protection Room by Room

GFCI protects people from shock, and AFCI protects the building from arcing fires. Both are needed in some rooms, and neither is needed in a few. NEC 210.8(A) sets the GFCI list and 210.12 sets the AFCI list.

Three details matter:

• Water counts in any room. A receptacle within 6 feet of a sink, tub or shower needs GFCI protection, even in a bedroom. So a bedroom circuit is normally AFCI only, unless a wet bar sits in the room.
• Appliances count. Dishwashers have needed GFCI protection since the 2014 edition. Many electricians trained on older cycles still miss it.
• Reachable matters. A GFCI must be where someone can test and reset it. A device behind a refrigerator does not qualify, so use a breaker.

Multiwire Branch Circuits

A multiwire branch circuit (MWBC) uses two hots on opposite legs and one shared neutral. It saves a cable, and it has rules because it can hurt someone.

On opposite legs, the neutral carries only the difference. With 15 amps on one hot and 10 amps on the other, the neutral carries 5 amps. If both hots land on the same leg by mistake, the neutral carries the sum, 25 amps, on a 12 AWG wire no breaker is watching. That overheats a conductor hidden in the wall.

Plan these points:

1. Opposite legs. Land the hots on breakers that sit on opposite legs. A two-pole breaker guarantees this.
2. One disconnect. NEC 210.4(B) requires all the hots to open at once. Use a common-trip two-pole breaker, or two single-pole breakers with an identified handle tie.
3. Pigtail the neutral. Under 300.13(B), removing a device must not open the neutral for anything downstream.
4. Group them. Keep the conductors of each MWBC grouped in the panel, as 210.4(D) requires.
5. Protection. A GFCI or AFCI on an MWBC has to be a two-pole breaker, because a single-pole device cannot read a shared neutral.

Warning: A neutral on a multiwire circuit can carry current while one breaker is off. Never open a shared neutral until both hots are off, locked and proven dead.

Panels and Subpanels

Working Space

NEC 110.26 requires clear space in front of a panel: 30 inches wide, 36 inches deep measured from the live parts, and 6-1/2 feet high. A panel cannot go in a clothes closet or a bathroom. Mark this space on the plan early, because a water heater or a shelf in it fails the job.

A Detached Garage Feeder

A panel fed from another panel is a subpanel. After the service disconnect, the neutral and the grounds stay apart.

1. Run a four-wire feeder: two hots, a neutral and an equipment grounding conductor (EGC).
2. Float the neutral bar in the garage panel. Do not install the bonding screw or strap.
3. Bond the ground bar to the panel enclosure.
4. Install a disconnect at the building and a grounding electrode, as NEC 225.31 and 250.32 require.

If the neutral and ground are bonded at the subpanel, normal neutral current flows on the metal parts and the EGC. That puts a shock hazard on every grounded surface.

Spaces for Later

Count the breakers, then add room. A panel with no spare spaces forces tandem breakers or a subpanel the first time the owner buys an EV. On existing homes, a load calculation decides whether the service can take a new load at all. Your supervisor owns that decision.

Where the Answer Changes

The local rule wins, even when you think the national code is better. You can always go beyond the minimum. You cannot go below what is adopted.

Common Mistakes

Check Your Understanding

1. A plan shows a wall oven fastened in place, drawing 11 amps, on a 20-amp circuit with one other receptacle. Is that acceptable?

No. Fastened-in-place equipment on a circuit that also feeds other outlets is limited to 50 percent of the rating, which is 10 amps. Give the oven its own circuit.

2. A hot tub heater is treated as a continuous 24-amp load. What is the smallest breaker?

24 x 1.25 = 30 amps. Then check the equipment's instructions, because they may set a different value.

3. A countertop runs 9 feet along a wall, with no sink or range in it. What is the fewest receptacles that can serve it?

Three. Each receptacle covers 24 inches in each direction, or 4 feet of counter. Two receptacles reach only 8 feet, so the last foot of a 9-foot counter would be out of reach.

4. Your MWBC feeds a kitchen, and you plan two single-pole dual-function breakers. Why is that wrong?

A single-pole GFCI or AFCI cannot work with a shared neutral. Use a two-pole device or two separate circuits, each with its own neutral.

5. A city has adopted the 2020 NEC, and an island is on the plan. Which rule do you use?

The 2020 rule as adopted, plus any amendment, even if 2023 asks for less.

Key Takeaways

• Confirm the edition and local amendments before you plan.
• Small-appliance, laundry, bathroom and garage circuits are required, at 20 amps.
• 14, 12 and 10 AWG pair with 15, 20 and 30 amps.
• A continuous load may use only 80 percent of a breaker, so a 20-amp circuit carries 16 amps.
• Receptacles run at 12 feet on walls and 4 feet along counters.
• Decide GFCI and AFCI room by room, and remember kitchens and laundries usually need both.
• A multiwire circuit needs opposite legs, one disconnect, and a pigtailed neutral.