PVC vs XLPE (Thermoplastic vs Thermosetting) SWA Cable: How to Choose

Two reels of steel-wire-armoured cable can look almost identical on the drum and behave very differently in the ground. The difference is the insulation: PVC (a thermoplastic) or XLPE (a thermosetting compound). It changes the current the cable can carry, how it copes with a fault, and what it costs. Here's how to choose, without over-thinking it.

The Core Difference: Chemistry and Temperature

PVC is thermoplastic — heat it enough and it softens, which is why its conductor is limited to a 70 °C maximum operating temperature. XLPE is cross-linked polyethylene, a thermosetting material: the polymer chains are chemically bonded so it doesn't re-soften, letting the conductor run continuously at 90 °C. That 20-degree headroom is the whole story behind XLPE's higher current ratings.

What the Higher Rating Buys You — and When You Can't Spend It

Because XLPE runs hotter, the 90 °C column in the current-carrying-capacity tables gives a meaningfully higher rating, so you can often use a smaller cable for the same load. But there are two catches that catch people out:

• Terminal temperature limits. Most switchgear and accessories are only rated for a 70 °C conductor at the termination, so unless the manufacturer confirms otherwise you must size on the 70 °C values anyway — see our guide to 90 °C cable on 70 °C terminals.
• Derating still applies. Grouping, ambient temperature and installation method reduce both cables from their headline figure — see cable derating factors.

Beyond Ampacity: The Practical Differences

• Fault withstand. XLPE tolerates a higher short-circuit temperature (around 250 °C) than PVC (around 160 °C), so it survives a bigger fault let-through for a given size — relevant to the adiabatic check.
• Fire behaviour. PVC produces more smoke and acidic gas when it burns; on escape routes and public buildings this pushes designs toward low-smoke halogen-free (LSZH) sheaths. Note the insulation and the outer sheath are separate choices — an XLPE-insulated cable can still have a PVC or LSZH sheath.
• Endurance and cost. XLPE generally has better thermal and mechanical endurance; PVC is often slightly cheaper and is well proven for general use.

Where SWA Fits In

Steel wire armour is a separate layer providing mechanical protection and a metallic path that usually serves as the circuit protective conductor. It's available with either insulation: in UK terms, BS 5467 is the XLPE (thermosetting) armoured cable and BS 6346 the PVC (thermoplastic) one. So "PVC vs XLPE" and "do I need SWA" are two independent decisions — pick the armour for the mechanical environment, and the insulation for the thermal and fault duty.

How to Choose — a Simple Default

• Default to XLPE/SWA (BS 5467) for most modern LV distribution: better ampacity headroom and fault performance for a small cost premium.
• Consider PVC (BS 6346) where cost matters, the duty is light, or you're matching an existing installation.
• Always confirm the terminal temperature limit before spending the 90 °C rating, and apply the grouping and ambient derating for the real route.

What This Means for Your Design

The insulation choice, the temperature basis and the derating factors all feed the same calculation — which is why they belong in the cable-sizing software, not in someone's head. Our ProDesign calculation packs state the cable type and temperature basis explicitly for every circuit, so the assumption is visible at design review. For a deeper treatment of the insulation types, the IET's Wiring Matters series is good further reading.