Introduction
Breaker sizing has no partial credit — a circuit is either correctly sized or it isn’t, and the errors hide in the steps people skip: the load that wasn’t inventoried, the continuous classification that wasn’t applied, the wire check that was assumed. This checklist is the final pass before you buy materials, call the electrician, or pull the permit. Work it top to bottom with the Breaker Size Calculator open beside you; every item should get a definite yes before the project moves forward.
Print it, or keep it on your phone at the panel. The ten minutes it takes are the cheapest insurance in the project.
The Breaker Sizing Checklist
1. Load inventory complete
- Every load on the circuit identified by testing (breaker off, walk the house) — not by trusting the panel directory.
- Nameplate watts, VA, or amps recorded for each load, with voltage (120 V or 240 V).
- Receptacle circuits: assumed loads documented, not assumed zero.
- Method refresher: the estimating guide.
2. Continuous loads classified honestly
- Each load marked continuous (expected 3+ hours at max current) or noncontinuous.
- Gray-zone loads (home office, dehumidifier, long-cycle equipment) treated as continuous.
- No load classified noncontinuous just to make the math fit a smaller breaker.
3. Calculation verified
- Watts/VA converted to amps at the correct voltage (A = W ÷ V).
- Continuous amps × 1.25, plus noncontinuous amps × 1.00.
- Result rounded up to the next standard size (15, 20, 30, 40, 50, 60, 100 A) — never down.
- Calculator result and hand calculation agree. (See the formula guide for the hand method.)
4. Wire check passed
- Selected breaker does not exceed the conductor’s protection limit: 14 AWG copper → 15 A max, 12 AWG → 20 A max, 10 AWG → 30 A max (NEC 240.4(D)).
- For larger sizes: 40 A → 8 AWG minimum, 50–60 A → 6 AWG minimum (copper).
- Derating considered: hot attic runs or crowded conduit may require heavier wire.
- Long runs checked for voltage drop with the Voltage Drop Calculator.
- Existing aluminum wiring flagged for electrician review — not sized by copper rules.
5. Protection type selected
- GFCI required? (Kitchen, bath, garage, outdoor, laundry, basement, crawl space — per adopted NEC edition.)
- AFCI required? (Most dwelling-unit living areas.)
- Breaker type chosen: standard, GFCI, AFCI, or dual-function — and budgeted (protection breakers run $40–$150).
- Protection requirements confirmed against the code compliance guide or the AHJ.
6. Panel compatibility confirmed
- Breaker brand and series listed for the specific panel (door label checked).
- Open slot available (or electrician-approved plan: tandem, subpanel, upgrade).
- Service capacity verified — the new load fits within the service rating (see the Electrical Load Calculator).
- No double-tapped breakers, no “fits but not listed” substitutions.
7. Code and permit boxes ticked
- Dedicated-circuit requirements checked (kitchen, bath, laundry, garage minimums).
- Permit requirement confirmed with the AHJ; permit pulled before work starts.
- Inspection scheduled (rough + final where applicable).
- Applicable NEC edition and local amendments confirmed — not assumed.
8. Installation quality planned
- Terminations to be torqued to manufacturer spec (torque screwdriver on hand).
- Boxes sized for fill; cable connectors and proper supports planned.
- Panel directory to be updated and every circuit legibly labeled (NEC 408.4).
- Post-install clamp-meter measurement planned to verify actual vs. calculated current.
9. Pro involvement decided
- Panel-interior work, service upgrades, aluminum wiring, and fault troubleshooting assigned to a licensed electrician — no exceptions.
- DIY scope (if any) confirmed legal with the AHJ and covered by the permit.
- Electrician’s quote checked against your own calculation — you know the right answer now.
- Decision framework refresher: the DIY vs. pro guide.
Quick-Reference Tables
| Continuous load (A) | × 1.25 | Breaker | Min. copper wire |
|---|---|---|---|
| 12.0 | 15.0 | 15 A | 14 AWG |
| 12.5 | 15.6 | 20 A | 12 AWG |
| 16.0 | 20.0 | 20 A | 12 AWG |
| 20.0 | 25.0 | 30 A | 10 AWG |
| 24.0 | 30.0 | 30 A | 10 AWG |
| 32.0 | 40.0 | 40 A | 8 AWG |
| 40.0 | 50.0 | 50 A | 6 AWG |
| Breaker | Max continuous load (80%) | Typical dedicated circuit |
|---|---|---|
| 15 A | 12 A | Lighting, general receptacles |
| 20 A | 16 A | Small appliance, bath, heater |
| 30 A | 24 A | Dryer |
| 40 A | 32 A | Range |
| 50 A | 40 A | Range, EV charger |
| 60 A | 48 A | EV charger, subpanel |
Related Guides
- Pro Tips — the planning habits behind each checklist item.
- Common Breaker Sizing Mistakes — what each checklist item is guarding against.
- Breaker Sizing FAQ — quick answers when a checklist item raises a question.
- Complete Breaker Sizing Guide — the full method the checklist verifies.
- Estimating Guide — building the load inventory item 1 demands.
Frequently Asked Questions
Do I really need to test what each breaker controls?
Yes — panel directories are wrong often enough that trusting them is a known error source. Ten minutes with the breaker off and a walk-through beats any label.
What if one checklist item fails?
Stop and resolve it before proceeding. A failed wire check means new wire or a smaller load; a failed panel-compatibility check means a different breaker; a failed permit check means a call to the AHJ. The checklist is a gate, not a suggestion.
Can I use this checklist for an inspection walkthrough?
It covers the items inspectors check most — sizing, wire pairing, GFCI/AFCI, labeling, panel compatibility — so it works well as a pre-inspection pass. It doesn’t replace the inspector’s authority or the adopted code text.
How often should I re-verify an existing panel against this list?
Whenever you add a load, change a breaker, or buy a house. Panels drift out of compliance over years of small changes — a re-check with this list catches the drift.
Get Your Number
Nine checks, ten minutes, zero ambiguity. Run your load through the Breaker Size Calculator, walk the checklist item by item, and don’t move to materials until every box is honestly ticked. The circuits that fail are almost never the ones that were checked — they’re the ones where somebody skipped a step.
Disclaimer: This checklist is a planning aid, not engineering advice or a substitute for code. Calculator results are planning estimates. Verify your plan with a licensed electrician and your local authority having jurisdiction (AHJ) before purchasing materials or starting work.
