What is cable ampacity?

Ampacity is the maximum current (in Amperes) that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

Why does distance limit cable capacity?

As distance increases, the resistance of the wire increases. Higher resistance causes a higher voltage drop at high currents. To keep voltage drop within safe limits, the maximum current must be reduced on longer runs.

Which is the limiting factor: thermal ampacity or voltage drop?

For short runs, the thermal ampacity of the wire is usually the limiting factor. For long runs, the voltage drop limit is reached first, requiring a derating of the maximum load or a larger wire.

Max Load Cable Calculator

Determine the maximum safe electrical load (Amps and kW) a cable can carry over a specified distance. Ensure the load does not exceed standard ampacity or the designated voltage drop threshold.

System Constraints

Source Voltage (V)

System Phase

Conductor Material

Max Drop Allowed (%)

Conductor Size (AWG / Metric)

One-Way Distance

Maximum Allowed Load

Max Current (Amps)

at voltage drop limit

Max Active Power

kW / kilowatts

Calculation parameters:

Voltage Drop Limit: -- V

Resistance: -- Ω/km

Max Load Cable Calculation Formula

We solve the basic Voltage Drop equation in reverse to calculate the maximum permissible current before hitting the drop limits:

Allowed Drop Limit (V_limit) = V_source × (Max_Drop_percent ÷ 100)

Single Phase (1φ): I_max = [V_limit × A] ÷ [2 × L × ρ]

Three Phase (3φ): I_max = [V_limit × A] ÷ [√3 × L × ρ]

Max Power (kW) = [V_source × I_max × PhaseFactor] ÷ 1000

• PhaseFactor: Single Phase = 1.0 (apparent power), Three Phase = √3 ≈ 1.732.

• Cable physical resistivity properties are modeled standard at 75°C.

Send output to:

How to use Max Load Cable Calculator

Select the circuit phase, system voltage, and conductor material (Copper or Aluminum).
Choose the cable size (AWG or Metric mm²) and enter the distance of the run.
Set the maximum allowed voltage drop percentage (default is 3%) to calculate the maximum safe load.

What is Max Load Cable Calculator?

When designing electrical circuits, cables must be sized to prevent overheating (based on the conductor's ampacity rating) and to limit voltage drop over long distances. While a wire size might be thermally safe for 20 Amps, a long run of 100 feet could result in an unacceptable voltage drop.

This calculator determines the limiting factor—either thermal ampacity or voltage drop (e.g. 3% limit)—and reports the maximum current and total power (kW) you can safely run through the circuit.

FAQ

What is cable ampacity?: Ampacity is the maximum current (in Amperes) that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.
Why does distance limit cable capacity?: As distance increases, the resistance of the wire increases. Higher resistance causes a higher voltage drop at high currents. To keep voltage drop within safe limits, the maximum current must be reduced on longer runs.
Which is the limiting factor: thermal ampacity or voltage drop?: For short runs, the thermal ampacity of the wire is usually the limiting factor. For long runs, the voltage drop limit is reached first, requiring a derating of the maximum load or a larger wire.

Max Load Cable Calculator

System Constraints

Maximum Allowed Load

Max Load Cable Calculation Formula

How to use Max Load Cable Calculator

What is Max Load Cable Calculator?

FAQ

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