Armoured Cable Size Calculator SWA

Steel Wire Armoured Cable Sizing | BS 7671 Compliant | XLPE/PVC

⚡ Load Input

⚡ Load Value

⚡ System Voltage

🔌 Phase Type

⚡ Power Factor (cos φ)

📏 Cable Length (metres)

📐 Installation Method

🌡️ Insulation Temp (°C)

🌍 Ground/Ambient Temp (°C)

°C

📉 Max Voltage Drop (%)

📖 Armoured Cable (SWA) Size Calculator

This armoured cable (SWA) size calculator helps you determine the correct steel wire armoured cable size for electrical installations. Compliant with BS 7671 (IET Wiring Regulations) and suitable for both XLPE and PVC insulated armoured cables.

Armoured cables (SWA) are used for underground installations, outdoor supplies, sub-mains, EV chargers, and industrial applications where mechanical protection is required.

📐 SWA Cable Sizing Formula

Single Phase: I = P × 1000 / (V × PF)
Three Phase: I = P × 1000 / (√3 × V × PF)
Voltage Drop: VD = (mV/A/m × I × L) / 1000
VD% = (VD ÷ V) × 100 ≤ 5%
Derating: Iz = It × Ca × Cg × Ci

📊 SWA Cable Current Ratings (XLPE 90°C)

Size (mm²)	2-Core (A)	3-Core (A)	Common Applications
1.5	27	23	Lighting, small loads
2.5	36	31	Socket circuits
4	49	42	Cookers, showers
6	62	53	EV chargers (7kW)
10	85	73	Sub-mains, EV chargers
16	110	94	Sub-mains, meter tails
25	146	124	Main tails
35	180	154	Main supplies
50	215	185	Large supplies
70	275	235	Industrial loads
95	335	285	Industrial loads
120	385	330	Heavy industrial

📌 SWA Cable Installation Methods

Method C: Clipped direct or on cable tray - highest current rating
Method B: In conduit or trunking on wall - moderate derating
Method D: Buried direct in ground - lower current rating due to thermal resistance
Method E: In free air - good cooling, high current rating

❓ Frequently Asked Questions

What cable size for a 7kW EV charger? ▼

A 7kW EV charger draws about 30A at 230V. For a typical 30m run, 6mm² SWA is recommended. For longer runs (>40m), 10mm² SWA is better to manage voltage drop.

What is the difference between SWA and NYY cable? ▼

SWA (Steel Wire Armoured) has steel wire armour for mechanical protection. NYY is a non-armoured cable with PVC insulation, suitable for indoor use only.

Can SWA cable be buried directly? ▼

Yes, SWA cable is designed for direct burial. It has steel armour for mechanical protection and can be buried without additional conduit.

What is the maximum length for a 10mm² SWA cable? ▼

For a 32A load at 230V, a 10mm² SWA cable can run up to about 75-80m before exceeding 5% voltage drop. Length depends on load and installation method.