Sizing of Wire — Stranded vs Solid, Ground Wire & 240 V Reference
Sizing of wire — picking the right AWG for a given amperage — is the single most-asked question in residential and light-commercial electrical work. This page covers stranded versus solid wire trade-offs, the ground-wire size chart per NEC §250.122, 240 V wire selection for ranges and EV chargers, the gauge-ampacity Q&A for 10 / 14 / 16 / 18 AWG, and a worked pool-pump wiring example. Reviewed by a licensed PE.
Wire calculator and sizing tools
The wire-size calculator picks the smallest NEC-listed conductor that satisfies both ampacity (NEC 310.16) and voltage-drop limits in one pass. The amp-to-wire chart gives a quick lookup table. The voltage-drop calculator handles long runs and unusual voltages (12 V DC, 48 V solar, 277 V industrial).
→ Wire size calculator · → Amp to wire size chart · → Voltage drop calculator
Wire sizing formulas
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- I_cont = continuous load (3+ hr at full value)
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- I_non-cont = non-continuous load
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- NEC §210.20(A) for branch, §215.3 for feeder
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- I_table = NEC Table 310.16 base ampacity
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- k_T = ambient-temperature correction (Table 310.15(B)(1))
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- k_fill = conduit-fill correction for > 3 CCCs (Table 310.15(C)(1))
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- L = one-way length (m)
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- I = load current (A)
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- R = conductor resistance per km (Ω/km)
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- NEC FPN limit: 3 % branch, 5 % combined
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- OCPD = overcurrent protective device (breaker / fuse) ampere rating
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- 15 A → 14 AWG Cu / 12 AWG Al EGC
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- 60 A → 10 AWG Cu / 8 AWG Al EGC
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- 200 A → 6 AWG Cu / 4 AWG Al EGC
Standards governing wire sizing
| Document | Scope |
|---|---|
| NFPA 70 (NEC) Article 310 | Conductor ampacity tables (310.15, 310.16, 310.17, 310.20) |
| NEC §240.4 / §240.4(D) | Conductor protection — small-conductor rule |
| NEC §250.122 + Table | Equipment grounding conductor sizing by OCPD rating |
| NEC Article 402 | Fixture wires (#16 / #18 in lamps and luminaires) |
| NEC Article 400 | Flexible cord (SO/SOOW, SJOOW) ampacity tables |
| NEC Article 680 | Swimming pools, spas, fountains — pool pump wiring |
| UL 83 / UL 854 / UL 44 | THHN/THWN, SE service entrance, XHHW-2 product standards |
| ABYC E-11 | AC and DC marine wiring — small-craft electrical systems |
| SAE J1128 | Low-tension primary cable for automotive 12 V / 24 V |
| IEC 60364-5-52 | International cable selection — current-carrying capacity |
Reference: ground wire size chart (NEC Table 250.122)
| OCPD rating (A) | Cu EGC (AWG) | Al EGC (AWG) |
|---|---|---|
| 15 | 14 | 12 |
| 20 | 12 | 10 |
| 60 | 10 | 8 |
| 100 | 8 | 6 |
| 200 | 6 | 4 |
| 300 | 4 | 2 |
| 400 | 3 | 1 |
| 500 | 2 | 1/0 |
| 600 | 1 | 2/0 |
| 800 | 1/0 | 3/0 |
| 1 200 | 3/0 | 250 kcmil |
Reference: 240 V wire selection by load
| Load | Amps (typical) | Breaker | Wire (Cu) |
|---|---|---|---|
| Electric water heater 4500 W | 18.75 | 30 A | 10 AWG |
| Electric dryer 5000 W | 20.83 | 30 A | 10 AWG |
| Electric range 8000 W | 33.3 | 40 A | 8 AWG |
| EV charger Level 2 9.6 kW | 40 | 50 A | 6 AWG |
| Hot tub 30 A | 30 | 50 A GFCI | 6 AWG |
| Sub-panel 60 A | 60 | 60 A | 6 AWG |
| Sub-panel 100 A | 100 | 100 A | 3 AWG / 1 AWG Al |
| Whole-house generator 200 A inlet | 200 | 200 A | 3/0 AWG / 250 kcmil Al |
- Identify the application Branch circuit (residential / commercial), feeder, motor lead, control wiring, or DC (12 V automotive, 48 V solar). Each has its own table — NEC Table 310.16 for AC building wiring; ABYC for marine; SAE J1128 for automotive.
- Pick the conductor type — solid or stranded Solid for fixed wiring up to 10 AWG (cheaper, easier to terminate under screw lugs). Stranded for 8 AWG and larger, anything that flexes (motor leads, machine wiring, robotics), or vibration-prone runs. Stranded has ~5 % higher AC resistance and slightly larger overall diameter.
- Determine the load and apply the continuous-load factor Sum continuous + non-continuous current; multiply continuous portion by 1.25 (NEC §210.20). For motors, use NEC Table 430.250 FLA. For HVAC, use nameplate MCA per NEC §440.4.
- Look up ampacity and verify NEC §240.4 protection Pick the smallest AWG whose 75 °C ampacity meets the load. Apply NEC §240.4(D) small-conductor rule (#14 → 15 A, #12 → 20 A, #10 → 30 A). Apply ambient and conduit-fill corrections.
- Verify voltage drop NEC FPN: 3 % branch / 5 % combined as recommended limits. The voltage-drop calculator handles every conductor. Long runs (> 50 ft for branch, > 100 ft for feeder) often require up-sizing beyond the ampacity-driven choice.
Worked example — 1.5 HP pool pump on a 240 V circuit
A 1.5 HP single-phase 240 V pool pump (FLA = 7.5 A from NEC Table 430.248). Pump runs > 3 hr daily — continuous load. 50 ft from sub-panel.
- Required ampacity (1.25× continuous): 1.25 × 7.5 = 9.4 A.
- Conductor: 14 AWG copper (20 A at 75 °C) is more than enough for ampacity, but NEC §680 requires GFCI protection and minimum 12 AWG for pool equipment branches per local interpretation — use 12 AWG copper.
- Breaker: 20 A GFCI single-pole or double-pole depending on motor wiring (most pool motors use a 240 V double-pole 20 A or 25 A breaker).
- EGC: Per NEC Table 250.122, 12 AWG Cu for 20 A breaker. The pool bonding grid uses solid 8 AWG Cu separately under §680.26.
- Voltage drop: 2 × 50 ft × 7.5 A × 0.00164 Ω/ft = 1.23 V → 0.51 % at 240 V — well under 3 % limit.
- Conduit: PVC Schedule 80 minimum 10 ft from pool wall (NEC §680.21).
Stranded versus solid wire trade-off
| Aspect | Solid copper | Stranded copper |
|---|---|---|
| Cost (per ft) | Lower (~10–15 % cheaper) | Higher |
| Outer diameter (4 AWG) | 5.19 mm | ~5.5 mm |
| AC resistance | Baseline | ~5 % higher (skin effect on individual strands) |
| Bending radius | Larger (≥ 6× OD) | Tighter (≥ 4× OD) |
| Vibration / flex life | Poor — work-hardens, breaks | Excellent |
| Best for | Building wiring 14–10 AWG, fixed runs | 8 AWG and larger, motor leads, robotics, machine wiring |
| Termination | Direct under screw lug | Use compression lug or ferrule |
Variants and related queries
Gauge wire — common pairings
The dominant breaker-to-gauge pairings: 15 A → 14 AWG; 20 A → 12 AWG; 30 A → 10 AWG; 40 A → 8 AWG; 50 A → 8 AWG (with 60 °C term., or 6 AWG); 60 A → 6 AWG; 100 A → 3 AWG; 200 A → 3/0 AWG. Always verify against NEC §240.4(D) small-conductor rule for AWG ≤ 10.
Ground wire — sizing with NEC §250.122
The equipment grounding conductor (EGC) is sized by the upstream overcurrent device, not by the load. NEC Table 250.122 gives the required AWG by OCPD rating — 15 A breaker → 14 AWG Cu EGC; 200 A → 6 AWG Cu. The EGC is generally smaller than the phase conductors because it carries fault current only for the fraction of a second before the OCPD trips. Bare or green-insulated copper is the most common form.
Amps gauge wire — quick-reference card
Most electricians memorise the "20-30-50-100" ladder: 20 A → 12 AWG, 30 A → 10 AWG, 50 A → 8 AWG, 100 A → 3 AWG. Add the small-conductor rule for #14, #12, #10 (cap at 15 / 20 / 30 A) and the basic ladder covers 90 % of branch and feeder circuits. The site amp-to-wire chart gives the full table including aluminum equivalents.
AWG wire — the gauge system
The American Wire Gauge ladder is geometric: each step decreases the diameter by ~1.123, halving the cross-sectional area every 6 steps and doubling the resistance. 4/0 (largest standard AWG) is roughly 11.7 mm diameter; 40 AWG (smallest) is 0.08 mm. Above 4/0 the system switches to circular-mil designations: 250 kcmil, 500 kcmil, 750 kcmil up to 2000 kcmil.
Drop wire (utility service drop)
"Drop wire" refers to the utility-owned overhead service-drop conductors that bring power from the pole-mounted transformer to the customer\'s service mast. Typical sizing: 1/0 aluminum triplex for 100 A, 2/0 aluminum for 150 A, 4/0 aluminum for 200 A. Sized by utility tariff rules rather than NEC, with weatherhead connections covered by NEC §230.32.
Frequently asked questions
- How many amps can 10 gauge wire handle?
- 10 AWG copper carries 35 A in the NEC 310.16 75 °C column and 40 A in the 90 °C column — but NEC §240.4(D) limits 10 AWG to a 30 A breaker regardless of insulation rating. So the practical answer for any branch circuit is 30 A. For 10 AWG aluminum, the 75 °C ampacity is 30 A, also capped at 25 A by §240.4(D).
- How many amps will 16 gauge wire handle?
- 16 AWG is below the NEC 310.16 minimum (NEC starts at 14 AWG for fixed building wiring) but is widely used in fixture wiring (NEC §402), portable cord (NEC §400), and control wiring. ABYC E-11 marine standard rates 16 AWG for 10 A continuous. SAE J1128 automotive table rates 16 AWG at 13 A. Indoor lamp cord rated 16 AWG SVT typically carries up to 13 A per UL 62.
- How many amps can a 18 gauge wire handle?
- 18 AWG carries about 10 A as fixture wire (NEC Table 402.5), 7 A as portable cord (NEC Table 400.5(A)), and 10 A in automotive 12 V wiring per SAE J1128. Like 16 AWG, 18 AWG is not a permitted branch-circuit conductor under NEC Article 310 — only Article 402 fixture wiring and Article 400 cord usage.
- How many amps is 8 gauge wire good for?
- 8 AWG copper: 50 A at 75 °C, 55 A at 90 °C in NEC Table 310.16. 8 AWG aluminum: 40 A at 75 °C, 45 A at 90 °C. The 50 A copper rating is what most installers use for electric ranges, EV chargers, and hot-tub feeders — pair with a 50 A breaker.
- How to wire pool pump?
- A typical 240 V single-phase 1.5 HP pool pump draws about 7.5 A FLA. Per NEC §680 Article: GFCI-protect the entire circuit, use 12 AWG copper THWN-2 in PVC conduit (rated 25 A at 75 °C, capped at 20 A breaker), bond all metal parts of the pump to the pool equipotential grid (NEC §680.26), and keep the conduit at least 10 ft from the pool wall unless buried in concrete. Always verify with the pump nameplate and the local AHJ before energising.
- How many amps can 14 gauge wire carry?
- 14 AWG copper carries 20 A in the NEC 310.16 75 °C column and 25 A at 90 °C — but NEC §240.4(D) caps 14 AWG at 15 A for breaker / fuse protection. Result: 14 AWG is the standard wire for 15 A residential lighting and outlet branches. 14 AWG aluminum is not commonly used for branch circuits (NEC §310.106(B) requires aluminum to be 12 AWG or larger).
- How many amps is 18 gauge wire good for?
- Same answer as "how many amps can a 18 gauge wire handle" above — 10 A as fixture wire, 7 A as portable cord, 10 A in automotive 12 V wiring per SAE J1128. For low-voltage DC circuits (12 V automotive, 48 V solar), the practical limit is voltage drop rather than ampacity — over a 30-foot 12 V circuit at 10 A, 18 AWG drops 4 V = 33 % which is unacceptable.
- How many amps 14 gauge wire 12v?
- In 12 V DC wiring (automotive, solar, marine), the ampacity limit comes from temperature rise rather than the NEC table — but voltage drop dominates at low voltage. ABYC E-11 marine table: 14 AWG carries 25 A continuous in engine compartment, 35 A general use. SAE J1128 automotive: 19 A. For practical 12 V loads at 14 AWG, voltage drop limits the run length to about 15 ft for a 10 A load to stay below 3 % drop.
Historic source — origin of the AWG ladder
The AWG ladder uses a geometric progression — each step decreases the diameter by a constant factor (≈ 1.123) — so going six AWG sizes apart halves the cross-sectional area and doubles the resistance. The system replaced dozens of inconsistent shop-by-shop gauges that preceded it.
Related calculators and references
Sources and further reading
- NFPA 70 — NEC, Articles 310, 240, 250, 400, 402, 680 (2023 edition).
- UL 83 — Thermoplastic-Insulated Wires and Cables; UL 854 — SE; UL 44 — XHHW-2.
- ABYC E-11 — AC and DC Electrical Systems on Boats.
- SAE J1128 — Low Tension Primary Cable (automotive).
- IEC 60364-5-52 — current-carrying capacity of cables.
- IEEE Std 141 — Recommended Practice for Electric Power Distribution for Industrial Plants (Red Book).