When installing or upgrading electrical systems, choosing the correct heat shrink sleeving is just as important as selecting the right cable. Whether you're working on a campervan, motorhome, or automotive system, proper sizing ensures a professional finish, mechanical protection, and long-term reliability.

Here’s a simple guide to sizing 2:1 ratio heat shrink based on cable size, overall thickness, and the correct sleeving size.

1️⃣ Understand Cable Size vs Cable Thickness

Cable size in mm² refers to the conductor cross-sectional area — this determines the current capacity. However, heat shrink sizing is based on the overall outside diameter (thickness in mm) of the cable, which includes the insulation.

• A 6mm² cable typically has an overall thickness of around 4.3mm.
• A 25mm² cable is around 10.1mm thick.
• A 95mm² cable is approximately 17.9mm thick.

Pro Tip: Always measure the actual outside diameter of your specific cable if possible, as insulation types and thicknesses can vary between manufacturers.

2️⃣ What Does 2:1 Heat Shrink Mean?

A 2:1 ratio means the tubing shrinks to exactly half of its supplied internal diameter when heated properly. For example:

• 6.4mm ID shrinks down to 3.2mm
• 12.7mm ID shrinks down to 6.4mm
• 25.4mm ID shrinks down to 12.7mm

The key rule is: The heat shrink must slide easily over the cable before shrinking, and shrink tight enough to grip the cable securely afterwards.

3️⃣ Matching Cable Size to Heat Shrink Size

Below are the most common pairings to help you get the perfect fit every time:

4️⃣ Simple Sizing Rule

• Choose heat shrink with an internal diameter slightly larger than the cable thickness.
• Make sure the fully recovered (shrunk) size is smaller than the cable thickness so it grips tightly.
• Allow extra diameter if you are shrinking over copper tube terminals, lugs, or connectors.

Need help selecting the right wiring, lugs, or heat shrink for your 12v setup? Call us on 023 935 52732 or WhatsApp us directly from the website for expert advice.