What wire size do I need for 70 amps?

For a 70-amp circuit, use 4 AWG copper wire or 3 AWG aluminum wire. This is per NEC Table 310.16 at 75°C insulation temperature. Common uses: large sub-panels and heavy commercial equipment.

What breaker do I need for 70 amps?

A 70-amp circuit uses a 70A double-pole circuit breaker. The breaker protects the 4 AWG copper (or 3 AWG aluminum) wire from overload. Double-pole breakers are used for 240V circuits and occupy two slots in the panel.

What can a 70-amp sub-panel power?

A 70-amp sub-panel can power a large workshop, an addition to a home, or multiple high-draw appliances simultaneously. It supports 240V circuits for welders, air compressors, EV chargers, and heating units alongside 120V outlets and lighting.

Can I use 6 AWG wire for a 70-amp circuit?

No — 6 AWG copper wire is rated for 65A at 75°C, which is below the 70A breaker rating. You must use at least 4 AWG copper or 3 AWG aluminum for a 70-amp circuit per NEC Table 310.16.

What Wire Size for 70 Amps?

Copper Wire

4 AWG

5.1894 mm · 21.1506 mm²

Aluminum Wire

3 AWG

5.8273 mm · 26.6705 mm²

Breaker: 70A · Based on NEC Table 310.16 (75°C insulation)

Common Uses for 70A Circuits

Large sub-panels, commercial equipment

4 AWG Copper — Key Specs

Diameter	5.1894 mm (0.204307")
Area	21.1506 mm²
Resistance at 20°C	0.8151 Ω/km
Weight	189.51 kg/km
Ampacity (75°C)	85 A

Important: For long wire runs, you may need to upsize the wire to compensate for voltage drop. NEC recommends keeping voltage drop under 3% for branch circuits. Use our voltage drop calculator to check.

Voltage Drop by Distance — 4 AWG Copper at 70A

One-way run	Drop	% of 240V	Verdict
25 ft	0.87 V	0.4%	Within the 3% branch-circuit target
50 ft	1.74 V	0.7%	Within the 3% branch-circuit target
75 ft	2.61 V	1.1%	Within the 3% branch-circuit target
100 ft	3.48 V	1.4%	Within the 3% branch-circuit target
150 ft	5.22 V	2.2%	Within the 3% branch-circuit target
200 ft	6.96 V	2.9%	Within the 3% branch-circuit target

Single-phase, 240V, full 70A load, 0.2484 Ω/1000 ft DC resistance (NEC Chapter 9, Table 8) at 75°C terminations. NEC 210.19(A) Informational Note recommends keeping branch-circuit drop at or below 3%, and 5% total across feeder plus branch circuit. Voltage drop is a performance recommendation, not a code requirement — but exceeding it causes dim lights, slow motor starts, and wasted energy.

Aluminum Feeder Specifications

Aluminum carries about 61% of the current of copper for the same cross-section, so a 70A feeder that takes 4 AWG copper needs 3 AWG aluminum — typically one to two gauge sizes larger.

Aluminum conductor	3 AWG
Ampacity (75°C, Table 310.16)	75 A
Copper equivalent	4 AWG (85 A)
Resistance	0.3029 Ω/1000 ft
Voltage drop at 100 ft, 70A	4.24 V (1.8% of 240V)

Installing aluminum correctly

Modern aluminum building wire must be AA-8000 series alloy (NEC 310.14(A)(1)). The 1960s-era AA-1350 alloy behind aluminum’s bad reputation is no longer permitted for branch circuits.
Terminate only on lugs and breakers marked AL/CU or AL9CU. Copper-only terminals are the most common failure point.
Apply an antioxidant compound to the stripped conductor before landing it, unless the termination is listed as not requiring it.
Torque every connection to the manufacturer’s value with a calibrated torque tool — NEC 110.14(D) makes this mandatory. Loose aluminum terminations are the primary cause of feeder failures.
Aluminum runs roughly half the weight and a third to half the cost of copper at feeder sizes, which is why it dominates service entrance and sub-panel feeders.

Circuit breaker size chart → Wire types and insulation ratings → NEC Table 250.122 — ground wire size → 4 AWG full specifications → Full AWG chart → Wire size calculator → Ampacity tables →