AC and harmonic effects
Skin, proximity, sheath, screen, neutral, and harmonic currents can increase effective loss beyond DC conductor resistance.
Engineering
Cable Loss Calculator
Calculate temperature-adjusted conductor resistance, circuit I²R loss, voltage drop, annual loss energy, linear heat release, and annual loss cost.
CONDUCTOR LOSS ACCOUNTING
Turn conductor temperature and route resistance into an auditable loss record
This calculator estimates steady resistive cable loss from current, one-way route length, conductor resistance at 20°C, an entered temperature coefficient, conductor operating temperature, phase count, and parallel paths. It then annualizes the instantaneous loss and assigns a user-entered energy price. The result is useful for screening conductor alternatives, not for predicting cable temperature or complete AC loss.
Operating cable loss (kW)—
Annual loss energy (kWh)—
Annual loss cost—
Resistance at temperature (ohm/km)—
Resistive voltage drop (V)—
Heat release (W/m)—
CONDUCTOR LOSS ACCOUNTING
Temperature-corrected cable loss ledger
Use the loss, heat-per-length, and energy consequences to compare conductor or route alternatives. Do not infer conductor temperature from the result; temperature is an input that must come from a thermal calculation, measurement, or credible design case.
| Loss step | Material condition | Circuit path | Operating duration | Calculated outcome |
|---|
CURRENT CALCULATION PROCESS
Formula, substitution, intermediate values, and reconciliation
RT = R20[1 + α(T − 20)]; Rpath = RTL/(1000nruns); Ploss = nconductorsI²Rpath; Eloss = Ploss × hours
Resistance is corrected from 20°C to the entered conductor temperature, scaled to route length, and reduced by equal parallel paths. I²R is applied to each loaded conductor; annual energy and cost are calculated only after instantaneous loss is reconciled.
Intermediate values remain unrounded until display formatting.
HOW TO USE THIS MODEL
Estimate loss without mixing temperature or path bases
- Select conductor resistance at 20°C for the actual material and cross-section, noting whether it is DC or AC.
- Enter conductor operating temperature from a documented thermal case or measurement.
- Use line current, one-way route length, phase arrangement, and matched parallel-run count on consistent bases.
- Review resistance, I²R loss, voltage drop, and heat per meter before applying hours and energy price.
- For variable operation, repeat by load interval and sum energy rather than multiplying peak loss by all annual hours.
CONDUCTOR LOSS ACCOUNTING FUNDAMENTALS
Physical quantities behind conductor loss
- Reference resistance
- Conductor resistance specified at a known temperature, commonly 20°C.
- Temperature correction
- Adjustment reflecting the material-dependent rise in resistance with temperature.
- Circuit path resistance
- Resistance of one phase path after length and parallel routes are considered.
- Joule heating
- Electrical energy converted to heat according to I²R.
- Linear heat release
- Modeled watts of conductor loss per route meter, not an allowable thermal rating.
- Annualized loss
- Instantaneous kW multiplied by representative time; validity depends on the load profile.
MODEL AND FORMULA
Correct resistance before applying current-squared heating
RT = R20[1 + α(T − 20)]; Rpath = RTL/(1000nruns); Ploss = nconductorsI²Rpath; Eloss = Ploss × hours
Resistance is corrected from 20°C to the entered conductor temperature, scaled to route length, and reduced by equal parallel paths. I²R is applied to each loaded conductor; annual energy and cost are calculated only after instantaneous loss is reconciled.
SYMBOLS AND DEFAULT CASE
Variable definitions, units, and starting assumptions
| Symbol or input | Meaning | Unit or default |
|---|---|---|
| R_T | Conductor resistance at entered temperature | ohm/km |
| R_20 | Reference conductor resistance at 20 C | ohm/km |
| alpha | Resistance temperature coefficient | per degree C |
| R_path | Equivalent one-way path resistance after parallels | ohm |
| P_loss | Instantaneous conductor loss | kW |
| E_loss | Loss energy over entered operating hours | kWh |
| phases | Circuit phases (1 or 3) | 3 |
| currentA | Line current (A) | 240 |
| lengthM | One-way route length (m) | 210 |
| resistanceOhmPerKmAt20C | Resistance at 20°C (ohm/km) | 0.125 |
| conductorTemperatureC | Conductor temperature (°C) | 70 |
| temperatureCoefficientPercentPerC | Resistance coefficient (%/°C) | 0.393 |
| parallelRuns | Parallel runs | 2 |
| operatingHours | Annual operating hours | 5000 |
| energyPricePerKwh | Energy price per kWh | 0.12 |
Percent inputs are converted to decimal factors once. The live calculation process above substitutes the current values in order, names intermediate quantities, reports the final result, and closes with a reverse or conservation check.
DEEP ENGINEERING ANALYSIS
Loss mechanisms beyond the basic conductor model
Connection resistance
Terminations and joints can create localized heating not represented by uniform ohms per kilometre.
Economic boundary
Energy price, demand charges, maintenance, outage risk, and conductor capital cost belong in a life-cycle comparison, not the I²R formula.
WORKED DECISION CASES
Two loss studies with different time bases
Continuous process line
A warm, highly loaded feeder operates near one duty for most of the year, making direct annualization reasonable after resistance temperature is verified.
Intermittent crane supply
Peak current is brief and frequent; the analyst sums loss across operating states rather than treating the peak as an 8,760-hour load.
TECHNICAL GLOSSARY
Cable loss terms
- Reference temperature
- Temperature at which the base resistance is specified.
- Conductor temperature
- Metal temperature governing resistance, distinct from surrounding ambient.
- Joule loss
- Heat produced by current flowing through resistance.
- Effective path resistance
- Resistance seen by one loaded phase after length and parallels.
- Load factor
- Relationship between actual time-varying demand and a reference maximum.
- Marginal energy price
- Cost assigned to an incremental kWh for the study.
EVIDENCE AND DATA LINEAGE
Retain temperature, resistance, and duty-cycle records
Keep conductor data sheet and resistance basis, material coefficient, measured or calculated conductor temperature, current RMS and harmonic record, phase and neutral loading, route survey, parallel-run equality, operating-hour or interval profile, energy tariff basis, units, and unrounded intermediate results.
LIMITS AND EXCLUSIONS
What the basic I²R loss excludes
- It omits dielectric, sheath, screen, circulating, skin, proximity, harmonic, neutral, joint, and termination losses unless embedded in the entered resistance/current.
- It assumes a fixed conductor temperature and does not solve thermal equilibrium or cyclic ampacity.
- The cost output excludes demand charges, escalation, discounting, capital cost, maintenance, and outage economics.
RELIABLE SOURCES
References for this method and its boundaries
FREQUENTLY ASKED QUESTIONS
Cable loss questions
Why correct resistance for temperature?
Metal resistance changes with temperature, so 20°C data can understate energized loss.
Why use one-way length?
The formula separately counts loaded conductors; using loop length as well would double-count the path in this model.
Does heat per meter predict cable temperature?
No. Temperature depends on heat transfer through insulation, surrounding media, spacing, and ambient conditions.
Can the energy price be zero?
Yes for a pure technical loss calculation; annual cost will then be zero while energy loss remains.
What if current changes every hour?
Calculate each interval’s I²R energy and sum it; loss at average current is generally not equal to average loss.
Does this include reactive current?
Enter actual RMS current, which includes the heating effect of both real and reactive current components.
IMPORTANT ENGINEERING NOTE
Loss reduction must preserve electrical and thermal compliance
Do not choose a conductor or operating current from energy savings alone. A qualified electrical professional must verify ampacity, voltage, protection, fault withstand, installation, thermal environment, power quality, terminations, governing code, and manufacturer requirements.