WireGaugeCalc Free calculator · NEC cited · works offline
Sizing A TBB Grounding Conductor
Sizing a TBB grounding conductor is fast with WireGaugeCalc, since you enter the backbone length and the calculator returns a copper conductor size.
The tool reads the run distance and the bonding rules, so you get a defensible TBB size without flipping through tables by hand.
Enter your numbers once and you have a size you can put on the print.
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.
Sizing a copper telecommunications bonding backbone conductor
The TBB grows with run length, so a longer backbone calls for a larger copper conductor.
WireGaugeCalc applies the bonding sizing steps to your length and shows the next standard conductor size.
You see why the size lands where it does, since the run distance drives the result.
What the calculator checks for the bonding backbone
A few inputs decide the TBB conductor size:
- Backbone run length from the entrance facility to each telecom room
- Copper conductor, since the TBB is a copper bonding path
- The next larger standard AWG size when a value falls between steps
- Conductor size stepping up as the distance increases
- A result you can mark on the bonding plan
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
Does the TBB conductor size change with the run length?
Yes. A longer backbone run calls for a larger copper conductor, so the size steps up as distance grows.
Is the TBB always copper?
The telecommunications bonding backbone is run as a copper conductor. Confirm conductor type and size against the current NEC and your local authority having jurisdiction before you install.
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.