1. What is Parallel Wire Capacitance?

Definition: This calculator computes the capacitance per unit length between two parallel cylindrical conductors.

Purpose: It helps electrical engineers and physicists determine the capacitive coupling between parallel wires in transmission lines or other applications.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( C \) — Capacitance per unit length (F/m)
• \( \epsilon \) — Permittivity of the medium (F/m)
• \( d \) — Distance between wire centers (m)
• \( r \) — Radius of the wires (m)

Explanation: The capacitance depends on the natural logarithm of the ratio of wire separation to wire radius, scaled by the permittivity of the surrounding medium.

3. Importance of Parallel Wire Capacitance

Details: Understanding this capacitance is crucial for designing transmission lines, minimizing crosstalk, and analyzing signal integrity in electrical systems.

4. Using the Calculator

Tips: Enter the permittivity (default 8.854×10⁻¹² F/m for vacuum), wire separation (must be > 2× radius), and wire radius. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical permittivity value for air?
A: The permittivity of air is approximately 8.854×10⁻¹² F/m, very close to vacuum.

Q2: Why must wire separation be greater than wire diameter?
A: The formula assumes wires don't touch (d > 2r). For d ≤ 2r, the physical situation changes completely.

Q3: How does insulation affect the calculation?
A: Insulation increases effective permittivity. Use the permittivity of the insulating material instead of air/vacuum.

Q4: Can this be used for twisted pair cables?
A: This is an approximation for twisted pairs; exact calculation requires more complex modeling.

Q5: What if my wires have different radii?
A: The formula changes to \( C = \frac{\pi \epsilon}{\cosh^{-1}\left(\frac{d^2 - r_1^2 - r_2^2}{2r_1r_2}\right)} \) for unequal radii.