Length of Pull Calculator

Length of Pull Formula:

\[ L = \frac{VD \times A}{2 \times \rho \times I} \]

Voltage Drop (VD):

volts

Cross-sectional Area (A):

m²

Resistivity (ρ):

ohm-m

Current (I):

amps

Length of Pull (L): meters

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1. What is a Length of Pull Calculator?

Definition: This calculator determines the maximum allowable cable length (pull) based on voltage drop, conductor properties, and current.

Purpose: It helps electrical engineers and technicians ensure proper voltage levels are maintained over cable runs.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ L = \frac{VD \times A}{2 \times \rho \times I} \]

Where:

\( L \) — Length of pull (meters)
\( VD \) — Voltage drop (volts)
\( A \) — Cross-sectional area (m²)
\( \rho \) — Resistivity (ohm-m)
\( I \) — Current (amps)

Explanation: The formula calculates the maximum cable length before voltage drop exceeds specifications.

3. Importance of Length of Pull Calculation

Details: Proper calculation ensures electrical systems operate within voltage tolerances, preventing equipment malfunction and power loss.

4. Using the Calculator

Tips: Enter the voltage drop, conductor area, resistivity (default 1.68×10⁻⁸ ohm-m for copper), and current. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is voltage drop?
A: The reduction in voltage that occurs as electricity travels through a conductor due to resistance.

Q2: Why is the length multiplied by 2?
A: The factor of 2 accounts for the round-trip path of current (both out and return conductors).

Q3: What's a typical resistivity value?
A: Copper is 1.68×10⁻⁸ ohm-m, aluminum is 2.65×10⁻⁸ ohm-m at 20°C.

Q4: How does temperature affect the calculation?
A: Higher temperatures increase resistivity. For precise calculations, use resistivity values at operating temperature.

Q5: What's an acceptable voltage drop?
A: Typically 3-5% of supply voltage for power circuits, but check local electrical codes.