WireGaugeCalc Free calculator · NEC cited · works offline
Breaker Amperage For 100 Ft 8 Gauge Wire
Breaker amperage for 100 ft 8 gauge wire is simple with WireGaugeCalc, since you enter the gauge and distance and it returns the safe load.
The calculator starts from the 8 AWG ampacity in NEC 310.16, then checks how a 100 foot run affects voltage drop at that current.
So you match the breaker to a wire you already plan to use.
Open the calculatorSmallest conductor whose ampacity meets the load, NEC Table 310.16. Field aid only, verify against the current NEC and your local authority having jurisdiction.
How 8 gauge ampacity sets the breaker over 100 feet
8 AWG copper carries 50 amps in the 75 degree column, so a 40 or 50 amp breaker is the usual fit.
Over 100 feet voltage drop grows with current, so the calculator may suggest staying near 40 amps to hold drop under 3%.
It shows both the ampacity limit and the distance limit so you choose the lower breaker.
What the 100 foot result depends on
The tool sizes the breaker from these inputs:
- Conductor set to 8 AWG
- Run length set to 100 feet
- Copper or aluminum material choice
- 50 amp ampacity ceiling for 8 AWG copper
- Voltage drop check at the chosen current
- A breaker suggestion at or below the limit
One app for every NEC calculation
WireGaugeCalc keeps the calculations you reach for most in one place:
- Voltage drop and wire sizing for any run
- Conduit fill for EMT, PVC, and RMC
- Box fill and junction box sizing
- Ampacity and temperature derating
- Motor circuit and load calculations
- Conduit bend offsets and saddles
Built for the field, works offline
The whole app runs on your phone, so it keeps working in a basement, an attic, or a job site with no signal.
There is no account to create and nothing to load. Open it, run the number, and get back to work.
- No signup and no signal needed
- Answers in a tap, not a spreadsheet
- Same tool on phone, tablet, and desktop
Every result cites the NEC article
Each answer shows the table or formula it came from, so you can check the method and learn the code as you go.
That makes the app useful on the job and during exam prep, since the reasoning is right next to the number.
Switch the code year your job runs on
Jurisdictions adopt the NEC at different times, so you can match the calculation to the code in force:
- NEC 2017, 2020, and 2023 tables
- Copper and aluminum conductors
- 60, 75, and 90 degree C terminations
- Single-phase and three-phase systems
Run the number, then get back to work
Stop flipping through a paper book or hopping between calculator sites. Enter your values, read the code-cited answer, and move on. Free to use, no signup.
Open the calculatorFrequently asked questions
What breaker can I use on 100 feet of 8 gauge copper?
8 AWG copper handles up to 50 amps, but a 100 foot run can push voltage drop high, so a 40 amp breaker is often the safer pick. Confirm with the current NEC and your local authority having jurisdiction.
Does 100 feet of 8 gauge really need a smaller breaker?
Not always, since voltage drop depends on the actual load, not just the breaker. The calculator shows the drop at your current so you can decide between 40 and 50 amps.
Is WireGaugeCalc free to use?
Yes. Every calculator is free to run with no signup. A paid tier adds saved projects, PDF reports, and extra code years, but the core math stays free.
Does it work without internet?
Yes. The app runs on your device, so it keeps working with no signal on a job site, in a basement, or in an attic.
Are the results code accurate?
Results follow published NEC tables and standard formulas, and each answer shows the article it came from. It is a field aid, not a stamp of approval, so verify against the current code and your local authority before you wire anything.
Which NEC code year does it use?
You can switch between NEC 2017, 2020, and 2023, since jurisdictions adopt the code at different times. Pick the year your job runs on.