What size wire do I need for a 175 amp breaker?

3/0 AWG copper is the smallest conductor our model estimates at or above 175 A using a 75 °C insulation rating; 4/0 AWG is required if the terminations are limited to 60 °C. In aluminium the equivalent is 4/0 AWG. Verify against the code edition adopted locally before installing.

Can I use aluminium wire on a 175 amp circuit?

Yes, where the terminations are rated for aluminium. Because aluminium carries roughly 78% of the current of the same copper size, a 175 A circuit steps up to 4/0 AWG and uses K = 21.2 in the voltage-drop formula instead of 12.9.

How far can a 175 amp circuit run?

On 3/0 AWG copper the 3% voltage-drop guideline is reached near 133 ft one-way at 120 V and 267 ft at 240 V. Longer runs need the next size or two up — length, not ampacity, decides most feeder sizes.

Is a 175 amp breaker sized at 100% of the load?

Only for non-continuous loads. A continuous load is designed at 125%, so 175 A of continuous current becomes 218.8 A of design current and lands on a 225 A device with conductors sized to match.

What is typically on a 175 amp circuit?

Commonly feeders for light commercial panels. The load type also drives the receptacle and disconnect ratings, not just the conductor size.

What Size Wire for a 175 Amp Breaker?

Conductor size, aluminium equivalent, derating and maximum run length for a 175 amp circuit — all derived from published conductor geometry and the voltage-drop formula.

Quick answer

A 175 amp circuit needs 3/0 AWG copper with 75 °C terminations, or 4/0 AWG aluminium. 4/0 AWG copper applies where equipment terminals are limited to 60 °C. Voltage drop reaches 3% at roughly 267 ft one-way on 240 V and 133 ft on 120 V.

Formula estimate

Copper @ 75 °C

3/0 AWG

Copper @ 60 °C

4/0 AWG

Aluminium @ 75 °C

4/0 AWG

3% drop @ 240 V

267ft

Conductor options for 175 A

Estimated ampacity of each candidate size, so you can see the margin you are buying.

Material / rating	Minimum size	Estimated ampacity	Margin over 175 A
Copper, 60 °C	4/0 AWG	195 A	+20 A
Copper, 75 °C	3/0 AWG	198 A	+23 A
Copper, 90 °C	2/0 AWG	192 A	+17 A
Aluminium, 75 °C	4/0 AWG	180 A	+5 A
Aluminium, 90 °C	4/0 AWG	202 A	+27 A

Ampacity estimated as I = 0.0670 × cmil^0.6505, scaled for insulation rating and material.

Source & method: Conductor areas come from the ASTM B258 relationship d = 5 × 92^((36 − n) / 39). Ampacity is a fitted physical model, not a reproduction of any code table, and runs within roughly ±8% of published values.

Maximum run length on 3/0 AWG copper

One-way distance before voltage drop passes the 3% and 5% guidelines.

System	3% limit	5% limit	Drop @ 100 ft
120 V 1Ø	133 ft	222 ft	2.24%
240 V 1Ø	267 ft	445 ft	1.12%
208 V 3Ø	267 ft	446 ft	1.12%
480 V 3Ø	618 ft	1,030 ft	0.49%

Source & method: VD = 2 × K × I × L / cmil single phase, 1.732 × K × I × L / cmil three phase, with K = 12.9 for copper. 3/0 AWG is 167,806 circular mils and 0.0618 Ω per 1000 ft at 20 °C.

Wire size by run length for 175 A

Ampacity sets the floor; distance is what actually forces the upsize on long runs. Smallest copper conductor that carries the load and still holds 3% drop.

One-way run	120 V 1Ø	240 V 1Ø	480 V 3Ø
50 ft	3/0 AWG	3/0 AWG	3/0 AWG
75 ft	3/0 AWG	3/0 AWG	3/0 AWG
100 ft	3/0 AWG	3/0 AWG	3/0 AWG
150 ft	4/0 AWG	3/0 AWG	3/0 AWG
200 ft	300 kcmil	3/0 AWG	3/0 AWG
250 ft	350 kcmil	3/0 AWG	3/0 AWG
300 ft	400 kcmil	4/0 AWG	3/0 AWG

Sized on both criteria at once: estimated 75 C ampacity and 3% voltage drop at the stated one-way distance.

Source & method: A dash means no listed size holds 3% at that distance and voltage — split the load, raise the system voltage, or move the panel closer.

Hot attics, conduit runs and bundling

What a 175 A circuit actually needs once ambient temperature and conductor count are applied.

Ambient	3 conductors	4–6 conductors	7–9 conductors
30 °C	3/0 AWG	4/0 AWG	250 kcmil
40 °C	4/0 AWG	250 kcmil	300 kcmil
50 °C	250 kcmil	350 kcmil	400 kcmil
60 °C	350 kcmil	500 kcmil	600 kcmil

Source & method: Ambient correction F = √((Tc − Ta) / (Tc − 30)) with Tc = 75 °C; bundling adjustment uses the standard stepped schedule (1.00 / 0.80 / 0.70). The conductor shown is the smallest copper size whose corrected ampacity still carries 175 A.

Where 175 A circuits are actually used

175 A is a commercial feeder rating used where the calculated load exceeds 150 A but a 200 A device would oversize the equipment being protected. It also appears as the maximum device on some transformer secondary and motor-control feeders.

Transformer secondary conductors are the notable case at this rating: they get specific protection rules rather than ordinary feeder treatment, and the primary device does not automatically protect the secondary conductors. Treat a 175 A transformer feed as a secondary-conductor problem, not a chart lookup.

175 A is common on commercial services and larger dwelling upgrades that stop short of 200 A because the meter base or the utility lateral limits the rating. The termination hardware at this level is normally listed for aluminium as well as copper, and the sizing question turns on whether the service allowance for a main power feeder applies to the specific run.

Continuous loads

A continuous load — one expected to run three hours or more, like commercial lighting or an EV charger — is designed at 125% of the load current. 175 A continuous becomes 218.8 A of design current, which lands on a 225 A overcurrent device and 4/0 AWG copper.

Frequently asked

What size wire do I need for a 175 amp breaker?: 3/0 AWG copper is the smallest conductor our model estimates at or above 175 A using a 75 °C insulation rating; 4/0 AWG is required if the terminations are limited to 60 °C. In aluminium the equivalent is 4/0 AWG. Verify against the code edition adopted locally before installing.
Can I use aluminium wire on a 175 amp circuit?: Yes, where the terminations are rated for aluminium. Because aluminium carries roughly 78% of the current of the same copper size, a 175 A circuit steps up to 4/0 AWG and uses K = 21.2 in the voltage-drop formula instead of 12.9.
How far can a 175 amp circuit run?: On 3/0 AWG copper the 3% voltage-drop guideline is reached near 133 ft one-way at 120 V and 267 ft at 240 V. Longer runs need the next size or two up — length, not ampacity, decides most feeder sizes.
Is a 175 amp breaker sized at 100% of the load?: Only for non-continuous loads. A continuous load is designed at 125%, so 175 A of continuous current becomes 218.8 A of design current and lands on a 225 A device with conductors sized to match.
What is typically on a 175 amp circuit?: Commonly feeders for light commercial panels. The load type also drives the receptacle and disconnect ratings, not just the conductor size.