Wiring and Protection
Wire Resistance Calculator
Use Wire Resistance when wire resistance is the quantity you need. Enter resistance per meter and conductor length, then compare the answer with the equipment or operating limits that apply to your case.
Set up the Wire Resistance case
Keep every entry on the units shown below.
Before entering values
Keep one-way and round-trip lengths clearly identified. If operating conditions changed between readings, calculate separate cases.
Use the displayed unit for every field and document conversions separately. For the companion conductor resistance calculation, open Conductor Resistance Calculator.
- Resistance per meter
- Default example: 0.007 Ω/m. Enter resistance per meter in Ω/m.
- Conductor length
- Default example: 30 m. Enter conductor length in m.
Wire resistance: calculation method
Here, Wire resistance is obtained from R = resistance per meter × length. Only Resistance per meter and Conductor length enter the numerical result.
With the current entries, the primary answer is 0.21 Ω. Preserve the raw inputs when replacing this example.
Calculate wire resistance from resistance per meter and conductor length. A later current per conductor decision can draw on Parallel Conductor Sharing Calculator.
Changing Resistance per meter
Change Resistance per meter from 0.007 Ω/m to 0.0084 Ω/m with every other entry unchanged. The result changes from 0.21 Ω to 0.25 Ω.
Do not average the two cases if either could define an operating limit.
How to use the result
Use Wire resistance as one quantified check within the larger decision. Compare it with the selected conductor and protective-device ratings.
Keep the input set beside the output so another reader can reproduce it.
What the formula leaves out
Temperature and return-path length must match the installation.
Depending on the application, account for code rules, manufacturer instructions, and field installation details. Resolve material omissions before selecting a standard size or rating.
Use the installed route length, conductor material, and actual current path.
A final reasonableness check
Review conductor length and the remaining entries as one case. If one value belongs to another temperature, load, or time period, separate the scenarios.
Use wire resistance alongside ampacity, voltage-drop, fault-current, and protection limits. Preserve the unrounded number until all dependent calculations and comparisons are complete.
If uncertainty remains, calculate labeled low and high cases. Include termination heating, installation method, ambient temperature, and grouping when those effects can change the decision.
Questions about Wire Resistance
What explains a gap between calculated and observed wire resistance?
Differences can come from termination heating, installation method, ambient temperature, and grouping, measurement uncertainty, or values taken under different conditions.
How should I compare two Wire Resistance cases?
Keep unaffected entries fixed so the cause of the difference remains visible. Use the installed route length, conductor material, and actual current path.