Speaker Wire Gauge

NEC Article 640 / AVIXA CTS-D — determine minimum AWG for any speaker run

System Type

Speaker Run

Amplifier Power

Speaker Impedance

Run Length

Loss Budget

Application

Recommendation

Minimum Passing Gauge

14 AWG

Background music, short-medium runs

Design Values

Z Load

8.00Ω

R_max Allowed

0.80Ω

Ω/kft Needed

2.67Ω/kft

Load Current

5.00A

Selected Gauge Analysis

Loop Resistance

0.76Ω

Power Loss

18.9W

Acoustic Loss

0.79dB

NEC Rating

15A

✓ 0.79 dB loss — acceptable

All Gauge Comparison

Gauge	Ω/kft	R_loop (Ω)	Loss (dB)	P_loss (W)	NEC Max A	Status
8 AWG	0.628	0.19	-0.20	4.7	40	✓ Pass
10 AWG	0.999	0.30	-0.32	7.5	30	✓ Pass
12 AWG	1.588	0.48	-0.50	11.9	20	✓ Pass
14 AWGrecommended	2.525	0.76	-0.79	18.9	15	✓ Pass
16 AWG	4.016	1.20	-1.22	30.1	13	✗ R too high
18 AWG	6.385	1.92	-1.86	47.9	10	✗ R too high

Reference: NEC Article 640 · AVIXA CTS-D Standard · Loss > 0.5 dB audible, > 1.0 dB unacceptable

References

Load Impedance (Z)

8Ω Direct: Z = speaker impedance

70V / 100V: Z = V² ÷ P

V = line voltage (70 or 100), P = tap power per speaker

Load Current (I)

8Ω Direct: I = √(P ÷ Z)

70V / 100V: I = P ÷ V

Used to check NEC ampacity of each gauge

Max Allowable Loop Resistance (R_max)

R_max = (loss% ÷ 100) × Z

Sets the worst-case resistance the wire can add before loss exceeds the budget

Required Wire Resistance (Ω/kft needed)

Ω/kft = (R_max ÷ (2 × run ft)) × 1000

Factor of 2 accounts for the full loop (hot + return conductors)

Actual Loop Resistance per Gauge

R_loop = (Ω/kft ÷ 1000) × (2 × run ft)

Calculated for each AWG gauge from its published resistance table value

Acoustic Loss (dB)

dB = 20 × log₁₀(Z ÷ (Z + R_loop))

Voltage-divider model; negative result = loss. > 0.5 dB audible, > 1.0 dB unacceptable

Power Dissipated in Wire (P_loss)

P_loss = I² × R_loop

Heat generated in the conductor; informational only

Pass Criteria

✓ R_loop ≤ R_max

✓ NEC ampacity > I

Both conditions must hold. Recommended = thinnest gauge that passes both