SpecCalc Hub
Cable Power Loss Calculator: I²R, kWh & Cost
Calculate resistive electrical cable losses and their energy cost. RF coaxial antenna attenuation in dB is a different calculation.
Preliminary estimate only. Not a code-compliance document, not installation approval, not final engineering design. Verify with qualified professional and local codes.
Enter the values
Client-side estimate. SpecCalc Hub does not store entered values.
Formula: P_loss = I^2 x R; E_loss = P_loss x hours
Reference formula
This simplified formula block is educational and depends on the page status and limitations.
P_loss = I^2 x R; E_loss = P_loss x hours
Assumptions
- Inputs are user-provided.
- The result is an informational estimate.
Limitations
- Professional verification is required before real-world use.
What this page helps with
Calculate resistive electrical cable losses and their energy cost. RF coaxial antenna attenuation in dB is a different calculation.
Use I²R to estimate conductor heating power, then multiply by operating time and tariff to estimate loss energy and cost.
Formula or method
R = ρ × L / A per conductor; total resistive loss is the sum of I²R in the current-carrying conductors. Energy = loss watts × operating hours / 1000; cost = kWh × tariff.
The working method on this page uses inputs such as System type, Current, One-way length, and Conductor material and reports outputs such as Circuit resistance, Power loss, and Energy loss. The formula, assumptions and limitations stay visible so the result can be reviewed instead of simply trusted.
This makes the page useful for comparison and documentation, but it does not automatically include every manufacturer coefficient, installation condition, environmental factor or local-code requirement that may matter in a real project.
How to use
- Enter the page inputs, starting with System type, and confirm that the units match the real scenario you are checking.
- Read the main output Circuit resistance together with the other reported values instead of focusing on only one number.
- Before a real decision, review the assumptions, limitations, source links and related tools on the same page.
Practical examples
A common question, worked through
A two-wire copper circuit, 20 m one way, 2.5 mm² and 10 A has loop resistance 0.275856 Ω at the model resistivity, so loss is 27.5856 W. At 8 h/day for 30 days it loses 6.620544 kWh; at 0.15 per kWh the cost is 0.9930816 in the selected currency.
Worked example with the form defaults
Example inputs: System type: Single-phase AC; Current: 16 A; One-way length: 30 m; Conductor material: Copper; Cross-section: 2.5 mm²; Operating hours: 100 h; Tariff: 0.15 per kWh; Currency: USD - US dollar. P_loss = I^2 x R; E_loss = P_loss x hours. Calculated outputs: Circuit resistance: 0.414 Ω; Power loss: 105.93 W; Energy loss: 10.593 kWh; Cost of losses: USD 1.59.
Common mistakes
- Using the page without checking units, document revision or the real operating context.
- Treating a preliminary result or reference table as a final engineering decision.
- Ignoring the source links, limitations and related tools needed for the next validation step.
Limitations
- This fixed-resistivity model does not certify cable temperature. A tightly wound cable reel changes cooling conditions; obey the reel’s wound/unwound load ratings rather than trusting I²R alone.
- Doubling current quadruples resistive losses at unchanged resistance. The model uses a fixed resistivity; loaded conductor temperature and AC effects may increase real losses.
- Professional verification is required before real-world use.
- The page does not replace official manufacturer documentation, local rules or site measurements.
- Separate professional verification is required for safety, protection, cable or installation decisions.
FAQ
Can this calculate antenna coax loss?
No. RF attenuation depends on frequency, cable construction, matching and connectors and is usually specified in dB per length. This tool models resistive power circuits.
Why do losses grow faster than current?
At a fixed resistance, P = I²R: doubling current multiplies resistive power loss by four. Temperature can also change resistance; the simplified comparison holds resistance fixed.
Can this estimate cable heating on a wound extension reel?
It estimates electrical resistive loss, not the resulting temperature. A wound reel has different cooling conditions; follow the product’s wound/unwound load ratings and installation limits.
Related tools
Explanation updated: 2026-09-16
Graphics
This calculator provides an estimate for informational purposes only. It is not a certified engineering design, electrical safety approval, or professional installation recommendation. Always verify final decisions with a qualified professional and applicable local codes.