Cable Selection Workflow
Follow this professional workflow to select cables correctly for your electrical installations:
Determine Load
Calculate the design current (Ib) for the circuit based on connected load
Size Cable
Use Cable Size Calculator to determine minimum cable size based on current and installation method
Check Voltage Drop
Verify voltage drop is within BS 7671 limits (3% lighting, 5% other)
Select Protection
Choose MCB/RCBO rating that protects the cable and provides discrimination
Key BS 7671 Requirements
- • Max 3% for lighting circuits (6.9V @ 230V)
- • Max 5% for other uses (11.5V @ 230V)
- • Ib ≤ In ≤ Iz (load ≤ MCB ≤ cable capacity)
- • I2 ≤ 1.45 × Iz (fault current protection)
Common UK Cable Types
Twin & Earth (T&E)
Most common for domestic fixed wiring (lighting, socket circuits)
SWA (Steel Wire Armoured)
For underground, industrial, and external installations
Single Core Cables
For conduit/trunking installations (commercial/industrial)
Flex & Appliance Cable
For connecting appliances and pendant lights
Installation Methods & Derating
Cable current-carrying capacity depends heavily on installation method (how heat dissipates):
Best heat dissipation - highest current capacity
Moderate - derating required for grouped cables
Poorest - significant derating required
Available Calculators
Cable Size Calculator
Calculate correct cable size with current carrying capacity and voltage drop compliance
Voltage Drop Calculator
Calculate voltage drop for single and three-phase circuits with BS 7671 compliance checks
Conduit Fill Calculator
Determine cable capacity in conduit according to BS 7671 Appendix 5 derating factors
Wire Length Calculator
Calculate total cable length and quantities needed for electrical installation projects
Circuit Breaker Selector
Select appropriate MCB or RCBO ratings for cable protection and compliance
Related Calculator Categories
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