1. What is an SWA Cable Voltage Drop Calculator?

Definition: This calculator estimates the voltage drop in Steel Wire Armoured (SWA) cables based on the mV/A/m rating, current, and cable length.

Purpose: It helps electricians and electrical engineers ensure proper voltage levels at the load end of SWA cable installations.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( VD \) — Voltage drop (volts)
• \( mV/A/m \) — Millivolts per amp per meter rating of the cable
• \( I \) — Current flowing through the cable (amps)
• \( L \) — Length of the cable run (meters)

Explanation: The voltage drop is calculated by multiplying the cable's mV/A/m rating by the current and length, then dividing by 1000 to convert mV to V.

3. Importance of Voltage Drop Calculation

Details: Proper voltage drop calculation ensures electrical equipment receives adequate voltage and complies with IET Wiring Regulations (BS 7671).

4. Using the Calculator

Tips: Enter the cable's mV/A/m value (from manufacturer specs), expected current load, and cable run length. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical acceptable voltage drop?
A: For lighting circuits, 3% of supply voltage (6.9V for 230V). For other circuits, 5% (11.5V for 230V).

Q2: Where can I find mV/A/m values for SWA cables?
A: From cable manufacturer datasheets or the IET On-Site Guide tables.

Q3: Does this account for three-phase systems?
A: This calculator is for single-phase. For three-phase, multiply result by √3 (1.732).

Q4: How does temperature affect voltage drop?
A: Higher temperatures increase resistance and voltage drop. Calculations are typically based on 70°C conductor temperature.

Q5: Should I include protective conductor in length?
A: No, use only the live conductor length (one-way distance).