1. What is an AC Voltage Drop Calculator for UK Standards?

Definition: This calculator estimates the voltage drop in AC electrical circuits according to UK wiring regulations (BS 7671).

Purpose: It helps electricians and engineers ensure voltage drops stay within permissible limits (typically 3% for lighting, 5% for other circuits).

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( VD \) — Voltage drop (volts)
• \( I \) — Current (amps)
• \( L \) — Cable length (meters)
• \( R \) — Resistance per unit length (ohms/meter)
• \( X \) — Reactance per unit length (ohms/meter)
• \( φ \) — Power factor angle (degrees)

Explanation: The formula accounts for both resistive and reactive components of impedance, with the power factor determining their relative contributions.

3. Importance of Voltage Drop Calculation

Details: Proper voltage drop calculation ensures equipment operates correctly, prevents overheating, and complies with UK wiring regulations (BS 7671).

4. Using the Calculator

Tips:

• Enter current in amps (design current or actual measured current)
• Use cable manufacturer data for R and X values
• Typical power factor angles: 30° (common for mixed loads), 0° (purely resistive), 90° (purely reactive)

5. Frequently Asked Questions (FAQ)

Q1: What's the maximum allowed voltage drop in UK installations?
A: BS 7671 recommends max 3% for lighting, 5% for other circuits from supply point to load.

Q2: Where can I find R and X values for cables?
A: Cable manufacturer datasheets or the IET Wiring Regulations (BS 7671) Appendix 4.

Q3: How does power factor affect voltage drop?
A: Lower power factors (larger angles) increase the reactive component's contribution to voltage drop.

Q4: Should I use design current or actual current?
A: For new installations, use design current. For existing circuits, actual measured current is better.

Q5: Does this account for three-phase systems?
A: This calculates single-phase drop. For three-phase, multiply result by √3 (1.732).