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Heavy Industrial Cable Sizing Engine

TMUK GROUP LTD

Heavy Industrial Cable Sizing & Parallel Run Report

BS 7671:2018+A3:2024 Compliance | Generated:

Heavy Mains Sizing Engine

Supports Parallel Runs & Massive Loads up to 3000 Amps

1. Heavy Electrical Load
Amps
2. Circuit Details
Metres
3. Environmental Factors
Required Cable Configuration -- Configuration: 1 run per phase Total Group Capacity (Iz): 0.00 A
Calculated Design Current (Ib) 0.00 A
Actual Voltage Drop 0.00 V Statutory Limit: --
ℹ Load Too Low For Heavy Mains: This engine is engineered exclusively for heavy industrial loads exceeding 100 Amps. For smaller currents, please switch to our standard All-in-One Circuit Designer.
ℹ Parallel Conductors Required: The current demand exceeds the safe thermal capacity of a single cable. The load has been divided evenly across identical parallel conductors per phase.
⚠ Voltage Drop Intervention: The calculated voltage drop exceeded statutory limits. The engine has automatically increased the cable cross-sectional area (or added parallel runs) to maintain BS 7671 compliance.
⚠ Extreme Load: Exceeds 6 parallel runs of 630mm². Consider a dedicated busbar trunking system or localized transformer.

Designing for Heavy Loads: Parallel Conductors (Over 1000A)

When engineering electrical systems for large industrial sites, factories, or commercial main intakes, the design current (Ib) frequently exceeds 1000 Amps. At these extremes, it is physically impossible and financially unviable to manufacture or install a single cable thick enough to handle the thermal load safely.

To comply with BS 7671 (Appendix 4), electrical designers use **Parallel Conductors**. This involves splitting the current across two or more identical cables per phase.

How Parallel Sizing Works

If your main switchboard has a design current of 1600A, this calculator divides that load. Instead of trying to find a non-existent 1200mm² cable, the engine might specify **three parallel runs of 300mm² single-core cables per phase**.

  • Current Division: In a perfectly balanced parallel system, the 1600A load divides equally. Each 300mm² cable only carries ~533A.
  • Voltage Drop Benefit: Adding parallel cables significantly reduces the resistance of the circuit. The total voltage drop is calculated for a single cable and then divided by the number of parallel runs, allowing for much longer runs without failing statutory voltage drop limits.

Single-Core AWA vs. Multicore SWA

For heavy mains above 400A, engineers typically transition from Multicore Steel Wire Armoured (SWA) cables to **Single-Core Aluminium Wire Armoured (AWA) or Non-Magnetic Unarmoured cables**.

Why? Because putting a single phase containing massive AC currents inside a magnetic steel armor creates eddy currents. These eddy currents act like an induction heater, rapidly overheating the armor and melting the cable. By using AWA (aluminium is non-magnetic) and grouping the three phases in a **Trefoil formation**, the magnetic fields cancel each other out safely.

Critical Engineering Disclaimer: Parallel cables must be identical in length, cross-sectional area, and material to ensure current divides equally. If they are not identical, one cable will take more current and overheat. This TMUK Group Ltd tool is a design aid. It assumes symmetrical loading and standard trefoil (Method F) spacing. A full bespoke design accounting for Zs, fault current (I²t), and localized grouping derating factors must be undertaken by an authorized engineer.