Chapter 17: Running a Brand-New Circuit

This is a big step up from extending an existing circuit. Now you're running cable all the way from the panel to a new location, installing a new breaker, and energizing the line for the first time. The skills are similar to extending an existing circuit, but the scope is larger and the panel work introduces new safety considerations.

This is also the project where the soft-nudge toward calling a pro starts to apply more strongly, depending on your situation. Pulling cable through finished walls for 50+ feet, drilling through finished framing in tight spaces, and installing a breaker in your panel are all skills that take time to develop. If your route involves significant fishing through finished walls, plan for a long weekend at minimum, and consider whether hiring out makes more sense.

That said, the work is well within reach for an attentive DIYer. Let's walk through it.

Estimated time: 4–12 hours depending on route complexity, panel configuration, and finish work needed. Cost: $50–200 in materials. Permit required: yes, in essentially all OKC metro jurisdictions.

When You Need a New Circuit

The most common reasons:

Adding capacity for a specific load: - Window or portable AC unit - Space heater - Workshop tools - Home gym equipment (treadmill, exercise bike with built-in display) - Aquarium or terrarium with heaters and lights - Sump pump or dehumidifier in a basement - Freezer or second refrigerator in a garage

Adding outlets to a new area: - New room or addition (always needs new circuits) - Finished basement or garage conversion - Detached structure (shed, workshop, ADU) - Multiple new outlets in a heavy-use area (kitchen island, home office)

Replacing inadequate wiring: - An overloaded circuit that constantly trips - Knob-and-tube circuits being retired - Aluminum-wired circuits being replaced with copper

The pattern: you need a dedicated circuit (no shared loads) or you need to reduce the load on an existing circuit by moving some outlets to a new circuit.

Pre-Project Planning

Before any tools come out, you need a plan.

1. Identify the Load

What will the new circuit serve? Estimate the maximum simultaneous load:

• Multiple receptacles for general use: 15A is typically fine
• A specific high-draw appliance (window AC, treadmill, etc.): check the appliance's nameplate. If it's over 1500W, plan for a 20A circuit with 12 AWG wire.
• A dedicated 240V appliance (welder, EV charger, water heater): different chapter (Chapter 23 for 240V projects).

2. Pick the Wire Size

• 14 AWG / 15A circuit: general lighting and receptacles, low-load applications
• 12 AWG / 20A circuit: kitchens, bathrooms (existing dedicated), workshops, anything with appliance-level loads

When in doubt, oversize. 12 AWG and 20A breakers cost only marginally more than 14 AWG and 15A, and they give you more headroom.

3. Check Panel Capacity

Your panel has a fixed number of breaker slots. Open the panel cover and count empty slots. If you have at least one (or two for a 240V circuit) empty slot, you can add a new circuit. If the panel is full, you have options:

• Use tandem breakers (two breakers in one slot) if your panel allows them. Many do; some don't. The panel's documentation will say.
• Add a sub-panel (Chapter 22) and feed the new circuit from there.
• Replace the panel with a larger one (Chapter 26).

4. Plan the Route

Same considerations as Chapter 16: from panel to first device, accounting for routing constraints. Typical routes:

• Panel in basement → up through floor → through wall cavity → to first box
• Panel in garage → through garage ceiling → into attic → down through wall to first box
• Panel in finished space → directly through finished walls (the hardest)

For long runs through finished walls (40+ feet), strongly consider hiring a pro. The labor cost may be similar to or less than what you'd spend on time.

5. Pull the Permit

Required for all new circuits in OKC metro. Apply, get the permit, then start work.

Required Tools and Materials

Tools (in addition to your basic kit and the tools from Chapter 16):

• Long auger drill bits (12" or 18", 5/8" or 3/4" diameter)
• Spade bits (1/2", 5/8", 3/4")
• Wire pulling lubricant
• Pull string (50+ feet)
• Fish tape (50 ft)
• Safety glasses (always)
• Insulated gloves (for panel work)

Materials:

• NM-B cable in the planned size and length (estimate generously; better to have extra than to need to splice mid-run)
• Cable staples
• Nail plates
• New breaker matching the panel brand and amp rating
• New device boxes for any new outlet locations
• New devices (receptacles, switches, etc.)
• Cover plates
• Wire nuts or Wago connectors

Special note on breakers: breakers are panel-specific. A Square D HOM (Homeline) breaker fits Square D HOM panels. A Square D QO breaker fits Square D QO panels. Eaton/Cutler-Hammer BR fits Eaton BR panels. Do NOT install a breaker that's not specifically rated for your panel, even if it physically fits. The internal contacts can fail, and you'll have inconsistent overcurrent protection.

Identify your panel brand by reading the label on the inside of the panel door (or on the panel itself). Buy breakers that match.

Step 1: Pull the Permit and Plan Documentation

Before starting:

1. Apply for the permit (Chapter 7).
2. Sketch the cable route and any new outlet locations on a simple floor plan.
3. Note the wire size, breaker amp rating, and the description of the work.
4. Once the permit is issued, post or save it (some cities require it posted at the work site, but for residential it's usually fine to keep with your records).

Step 2: Identify and Cut In the New Box(es)

Same procedure as Chapter 16. Use the stud finder, locate cavities, mark and cut openings for each new box. Verify there are no obstructions.

If you're installing multiple new outlets, plan their daisy-chain order: which one is first (closest to the panel), which is second, and so on. This affects how you'll route the cable.

Step 3: Plan the Cable Path from Panel to First Box

This is often the most complex part. Walk through the route mentally (or physically with a notebook):

1. Cable exits the panel at a top or bottom knockout (small circular punch-out in the panel housing).
2. Cable goes through whatever space is adjacent to the panel (basement, garage, utility room).
3. Cable transitions from that space into wall cavities, attic, or other routing space.
4. Cable arrives at the first new box.

For each segment, plan how the cable will be supported, what holes you need to drill, and where nail plates are needed.

A practical tip: route the cable in the "easy" direction first. From an unfinished basement up to a wall, easier than from a wall down to a basement. From an attic down through a wall cavity is easier than from a wall up to an attic. Plan to start the run in the accessible space and feed it into the harder space.

Step 4: Drill the Required Holes

Common drilling tasks for a new circuit:

• Through the wall plate (where the wall meets the floor or ceiling). Use a long bit, drill through the plate, and have the bit emerge in the basement, attic, or garage on the other side.
• Through studs in the wall cavity (for horizontal runs through the wall). Use a long auger bit through the box opening or through a small inspection hole.
• Through joists or rafters (for runs across ceiling/floor cavities). Drill at least 2" from the bottom edge of a joist (where load-bearing forces are highest); never drill in the bottom 1/3 of a structural joist.
• Through the panel knockout (for cable entry into the panel itself). Use a hammer and screwdriver to break out the knockout disc; install a cable connector or grommet to protect the cable.

For each hole, install a nail plate if the cable will pass within 1.25" of the framing's face after drilling.

Step 5: Pull the Cable

The procedure is the same as Chapter 16 but at greater length. Start at the panel end and pull toward the boxes, or vice versa, depending on which direction is easier.

A useful technique for long pulls:

1. Run a pull string through the entire route first (using the fish tape if needed).
2. Tie the cable to the pull string at one end.
3. From the other end, pull the string, drawing the cable through.
4. Use lubricant for any tight sections.

Use lubricant for any tight sections. Pull soap reduces friction by 30–50%, and on long runs, this is the difference between getting the cable through and giving up.

If the cable gets stuck mid-pull, don't force it. Usually, going back and forth (pull a foot, push a foot) helps it work past the obstruction. If it's truly stuck, you may need to cut access into the wall to reach it. Better to lose some drywall than to damage the cable.

Step 6: Secure the Cable

Per Chapter 16:

• Staples within 12" of every box, every 4.5 feet on continuous runs.
• Nail plates wherever the cable crosses through a hole within 1.25" of framing face.
• Don't crush the cable with staples.

Step 7: Make Connections at Each Box

Working from the panel end outward (or from the far end back to the panel; either works):

For each device box:

1. Pull the cable into the box, leaving 6–12" of free conductor inside.
2. Strip outer jacket and individual wire insulation as needed.
3. Connect the device: - For receptacles: black to brass, white to silver, bare/green to ground. - For switches: black to one of the two brass screws (the other gets the switched-output wire); ground to green. - For combo devices, follow the device-specific instructions.
4. For middle-of-run boxes (cable comes in and goes back out to the next device), pigtail the wires per Chapter 10.
5. Tug-test all connections.
6. Push device into box, screw to box, install cover plate.

Step 8: The Panel Connection (The Critical Part)

This is the step that makes new circuits different from extending existing ones. You're now opening your panel and adding a new breaker.

Safety first. Read Chapter 3 again before starting this part. Specifically:

• Wear insulated gloves and safety glasses.
• Work with one hand at a time when possible.
• Plan your moves so you never reach over the line-side lugs at the top of the panel.
• Have a flashlight or headlamp; the panel will be partially dark with the main breaker off.

Procedure:

1. Turn off the main breaker. This kills all the bus bars and branch circuits. The line-side lugs above the main are still live.
2. Three-test verify that the bus bars are dead. Check the screws on a couple of existing breakers to confirm.
3. Remove the dead front cover. Several screws around the perimeter. Set the cover aside carefully.
4. Identify the empty breaker slot you'll use. It should align with a tab on one of the bus bars.
5. Install the new cable into a knockout. Punch out the knockout, install a cable connector or grommet, push the cable through, and tighten the connector.
6. Strip the cable's outer jacket so that 6–12 inches of conductor are exposed inside the panel. The jacket should end where the cable enters the panel; don't have jacket inside the panel itself.
7. Route the conductors to their destinations: - Hot (black) wire to the new breaker. - Neutral (white) wire to the neutral bar. - Ground (bare or green) wire to the ground bar.
8. Cut wires to length with a few inches of slack. Strip the ends to expose 5/8" of conductor for each connection.
9. Connect the neutral. Insert the bare end of the white wire into an empty terminal on the neutral bar. Tighten the screw firmly.
10. Connect the ground. Same procedure on the ground bar. Tighten firmly.
11. Install the new breaker:
    • Turn the breaker to OFF before installing.
    • Connect the hot wire to the breaker's terminal: insert the bare end into the terminal, tighten the screw firmly.
    • Clip the breaker onto the bus bar tab. It should snap into place. The breaker handle should align with the other handles in the panel.
12. Verify connections: tug-test the wires at the breaker, neutral bar, and ground bar. They should be firmly held.
13. Reinstall the dead front cover. Make sure the cover lines up correctly with the breaker handles.
14. Turn the main breaker back ON.
15. Turn the new breaker ON. It should stay in the ON position. If it trips immediately, you have a fault somewhere. Turn it back off and diagnose.

Step 9: Test the New Circuit

1. At each new outlet: plug in your tester. Should indicate correct wiring.
2. Plug in a load at one of the outlets. Confirm power.
3. Test all outlets on the new circuit.
4. Test GFCI function if you installed a GFCI receptacle.
5. Test AFCI function if you used an AFCI breaker (press the test button on the breaker; the breaker should trip).

If everything works, you're ready for inspection.

Step 10: Schedule and Pass Inspection

Schedule the rough-in inspection BEFORE patching any drywall. The inspector needs to see:

• Cable runs (properly stapled, supported, with nail plates)
• Box connections (proper strip lengths, secure terminations)
• Panel connections (proper wire sizes, secure terminations, breaker installation)

After rough-in passes, patch drywall, install devices, and schedule the final inspection.

The final inspection verifies the work is complete and operational. Have your tester ready, and walk the inspector through the new circuit if asked.

Common Failure Points

The most common DIY failures on new-circuit projects:

• Wire size doesn't match breaker size. 14 AWG on a 20A breaker. (We've covered this five times now. Still the most common failure.)
• Cable not stapled per code. Especially in basement and attic runs.
• Box fill exceeded. Too many wires in too small a box.
• No GFCI or AFCI where required. New circuits in living areas need AFCI; new circuits in wet areas need GFCI.
• Loose connections at the panel. Wires not fully tightened on breaker, neutral bar, or ground bar.
• Cable jacket inside the panel. Code requires the jacket to end at the cable entry point; only individual conductors should be inside the panel.
• Cables not going through cable connectors at the panel. Bare cable directly through a knockout damages the cable; a connector is required.

When to Strongly Consider a Pro

Some warning signs that this project is over your head:

• The panel is full and you don't know how to add capacity.
• The cable run is over 50 feet through finished walls.
• The panel is unfamiliar (not Square D, Eaton, or another major brand) or has visible damage.
• You're not confident about which conductor goes where in the panel.
• The panel has aluminum wiring or other unusual conditions.

For these, the cost of professional work is genuinely worth it. The downside risk of a bad panel connection is severe, and pros do this work routinely.

What's Next

Chapter 18 covers exhaust fan installation: bath and kitchen vent fans. Chapter 19 covers outdoor electrical work in detail. Chapter 20 covers hardwiring new appliances. Chapter 21 covers smart home wiring.