Generator Cable Size Calculator: Find the Right Wire Gauge

⚡ Generator Cable Size Calculator

Find the correct wire gauge (AWG) for your generator based on load, distance & voltage

📌 Quick Presets

🔧 Calculator Inputs

Unit System

Phase Type

Generator Power (Watts)

Voltage (V)

Cable Run Distance (ft)

Conductor Material

Power Factor

Max Allowable Voltage Drop (%)

Safety / Derating Factor

Ambient Temperature

Conduit / Bundling Factor

Insulation / Cable Type

✅ Cable Sizing Results

📊 Wire Properties by Material

1.68

Cu Resistivity (nΩ·m)

2.82

Al Resistivity (nΩ·m)

90°C

Max Wire Temp (THWN)

NEC 310

NEC Ampacity Table

125%

NEC Continuous Load Rule

Recommended Max V-Drop

1.5x

Cu to Al Size Ratio

12 AWG

Minimum Branch Circuit

📋 AWG Copper Wire Ampacity & Resistance Reference

AWG	mm² (approx)	Max Amps (60°C)	Max Amps (75°C)	Max Amps (90°C)	Resistance (Ω/1000ft)	Typical Use
14 AWG	2.08	15A	20A	25A	3.07	Light circuits
12 AWG	3.31	20A	25A	30A	1.93	15A outlets
10 AWG	5.26	30A	35A	40A	1.24	Small generators
8 AWG	8.37	40A	50A	55A	0.778	Mid generators
6 AWG	13.3	55A	65A	75A	0.491	Large generators
4 AWG	21.1	70A	85A	95A	0.308	Heavy loads
3 AWG	26.7	85A	100A	110A	0.245	Sub-panels
2 AWG	33.6	95A	115A	130A	0.194	Main service
1 AWG	42.4	110A	130A	150A	0.154	Large service
1/0 AWG	53.5	125A	150A	170A	0.122	Industrial
2/0 AWG	67.4	145A	175A	195A	0.0967	Industrial
3/0 AWG	85.0	165A	200A	225A	0.0766	Large industrial
4/0 AWG	107	195A	230A	260A	0.0608	Heavy industrial

📋 Generator Power vs Recommended AWG (Copper, 240V, 50ft)

Generator Size	Rated Amps	Min AWG (NEC)	Recommended AWG	Extension Cord Size	Notes
1000–2000W	8–17A	14 AWG	12 AWG	12 AWG	Standard household
2000–3500W	17–30A	12 AWG	10 AWG	10 AWG	Size up for long runs
3500–5000W	30–42A	10 AWG	8 AWG	8 AWG	Include 125% NEC factor
5000–7500W	42–63A	8 AWG	6 AWG	6 AWG	Hardwired preferred
7500–10000W	63–84A	6 AWG	4 AWG	N/A hardwire	Transfer switch required
10000–15000W	84–125A	4 AWG	2 AWG	N/A hardwire	Licensed electrician
15000–20000W	125–167A	2 AWG	1/0 AWG	N/A hardwire	Licensed electrician

📋 Cable Type Specifications

Cable Type	Max Temp	Voltage Rating	Wet/Dry	Best Use
THWN-2	90°C	600V	Both	Conduit wiring
SOOW	60°C	300V	Both	Portable generator cords
SJOOW	60°C	300V	Both	Light portable use
USE-2	90°C	600V	Both	Underground / direct burial
XHHW-2	90°C	600V	Both	High temperature, conduit
SER	75°C	600V	Dry	Service entrance
SEU	75°C	600V	Dry	Service entrance, above ground

📋 Common Generator Cable Run Scenarios

Scenario	Power	Distance	Voltage	Recommended AWG	V-Drop @ Full Load
Emergency Home Backup	5000W	75ft	240V	6 AWG Cu	~2.4%
RV / Campsite	3000W	50ft	120V	10 AWG Cu	~2.9%
Construction Site	7500W	100ft	240V	4 AWG Cu	~2.8%
Standby Whole Home	12000W	50ft	240V	2 AWG Cu	~1.6%
Portable Small Gen	2000W	25ft	120V	12 AWG Cu	~1.8%
Industrial 3-Phase	15000W	100ft	480V	6 AWG Cu	~1.2%

💡 Tip 1 — Always Size Up: When your calculated current falls between two AWG sizes, always select the larger wire (lower AWG number). For runs over 100ft, go up at least one AWG size beyond the minimum to keep voltage drop within the 3% NEC recommendation.

💡 Tip 2 — Calculate Total Circuit Length: Voltage drop depends on the total circuit length — that means both the hot wire AND the return (neutral/ground) wire. Always double your one-way cable run distance when calculating voltage drop. A 50ft run is actually 100ft of total conductor.

⚠️ Safety Notice: Always follow local electrical codes and NEC guidelines. Generator wiring must be performed by a licensed electrician for permanent installations. Never exceed the rated ampacity of any wire or cable. Use a proper transfer switch — never backfeed utility power. Verify all connections are tight and properly insulated before energizing.

Election of the right size for the cable of the generator is really important. If you use wrong cable, it can cause failure or even dangerous cases. Moreover, that can damage the generator itself and the connected devices when the drop of voltage becomes too big.

So it really matters to choose it correctly from the first time.

Pick the Right Wire Size for Your Generator

Check the nameplate of the generator as good starting point. This label points the voltages of the system in volts and the power of the generator in watts. From that, it is possible to figure out the amps.

When you know the number of amps multiply it by 1.25 to follow the rule of 80% according to NEC. Like this you receive the needed size for the wire, that ensures safe mode. Later, asking a wire expert will help to specify the right cable size.

For the most common home uses, sizes of wires between 14 AGW and 6 AGW is usual. Even so, the exact size depends on factors like voltage, electricity and especially the length, that the cable must cover. Knowing the current force and the distance allow to estimate teh right wire size.

Length really affects a lot. Cable of 10 AGW typical L14-30 works well until around 65 feet. So, if the way passes 50 feet and reaches 125, better choose 8 AGW.

For 30-amp setup with 75-foot cable, 10 AGW actually is too little at that distance. It only lasts until 25 amps, before the fuse bursts. Rather, 8 AGW wire is necessary.

Longer cable from 14 AGW will heat more quickly, so always pick shorter lengths with smaller wires.

For 50-amp systems, 6 AGW is the usual choice. But if the run passes 100 feet, it requires 4 AGW copper. With aluminium, go to 3 AGW.

One calculation using a tool four wire size showed, that 6 AGW copper works for single phase way, 60-foot in pipe at 240V and 50 amps with under 3% voltage drop.

If the voltage of the generator is 120/240V, probably the cable is 10/4. Doubling the length of the cable requires to grow the size or keep the drop of voltage under load. So, 8 AGW or 6 AGW.

For 24 kW generator, that commonly means 100-amp service. The base is size 1 aluminium, before considering the drop of voltage. Stay under 3% drop allows around 180 feet withthis setup.

Some folks prefer to use bigger wire size, even if the current need does not require it. Choosing 8 AGW or 6 AGW leaves space for a stronger generator later. It is always smart to match the cable size to the strongest output of the generator.

Author

Thomas Martinez

Hi, I am Thomas Martinez, the owner of ToolCroze.com! As a passionate DIY enthusiast and a firm believer in the power of quality tools, I created this platform to share my knowledge and experiences with fellow craftsmen and handywomen alike.

View all posts