how does heat shrink tubing work?

guide to heat shrink tubing

Heat shrink works by creating a protective seal around an electrical wire or connection.  It is made from a substance that shrinks in diameter when heated creating a secure seal.  It is used in electrical work to protect wires, terminals and connections against moisture and abrasion.

What is Heat Shrink Tubing?

heat shrink tubing different sizes

Heat shrink tubing is used to insulate and protect electrical wires and connections.  It provides excellent electrical insulation and protection against abrasion and environmental contaminants such as dust and moisture.  It is commonly used when working with electrical wires, connections, joints and terminals.  It is a shrinkable plastic tube that is positioned over the area requiring protection.  It is then heated - and it shrinks into place providing a secure layer of external protective cover.

How Do You Use Heat Shrink Tubing?

Firstly, the unshrunk piece of tube is fitted to the wire before the connection is made.  Once the connection is complete, slide the tubing into place, positioning it carefully over the area that requires protection.  Silicone lubricant can be used to help position the tubing if the fit is tight.  This will not compromise the seal or connection.  Once in position, the tubing is heated to shrink it firmly into position.  Heat shrink tubing contracts up to one half of its original diameter depending on the type of heat shrink used.

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At What Temperature Does Heat Shrink Tubing Shrink?

shrinking heat shrink tubing

Most heat shrink tubing will shrink when heated to a temperature of 90°C.  The vast majority of heat shrink on the market is made from a substance called polyolefin.  This material has a shrink temperature of approximately 90°C.  Some tubing is constructed from a material called PTFE (aka. Teflon).  This type of tubing requires a much higher shrink temperature of 250°C.  This type of tubing is used in situations where the cable and wiring is going to be exposed to very high temperatures - eg: the wiring in temperature probes, metal rollers and heavy engineering equipment.

What is Adhesive Heat Shrink?

Adhesive heat shrink is tubing that comes with an adhesive liner to help it stay in place once applied.  The adhesive layer is made from a thermoplastic material that is coated onto the inside of the tube.  It ensures a better seal and stronger adhesion when in position.  It is a good choice for delivering a more permanent seal for heavier and more critical wires. The tubing is thicker and less flexible so it gives an increased level of protection to the wires and cables it covers.

What Size Heat Shrink Do You Need?

To determine the correct size of tubing you need - you should first measure the diameter of the cable to be covered.  Make sure you measure the cable at its widest part.  Then add about 30% onto this measurement to select the correct size of heat shrink tubing to use.  Bear in mind the shrink ratio of the tubing.  A 2:1 ratio means the tubing will shrink to half its size while 3:1 ratio means it will shrink to one third its size when heat is applied.  See below a quick reference guide for tubing sizes based on wire gauge.

  • 12 Gauge Wire - 5mm tubing with a .198 inch diameter
  • 14 Gauge Wire - 5mm tubing with a .198 inch diameter
  • 16 Gauge Wire - 3mm tubing with a .118 inch diameter (2:1 shrink ratio)
  • 18 Gauge Wire - 3mm tubing with a .118 inch diameter (2:1 shrink ratio)

Heat Shrink Tubing Types

Heat shrink tubing comes in two different types - single wall and dual wall.  They are sometimes referred to as thin wall or double wall.  Single wall, (thin wall tubing), is a good all rounder for insulating and protecting electrical cable.  It is a strong and robust heat shrink.  Double wall, (dual wall tubing), is the preferred option when extra protection is needed from corrosive and abrasive forces.   It contains an additional adhesive layer that provides a greater seal against any moisture.  Double wall is a step-up in terms of level of protection.

How Do Heat Shrink Connectors Work?

blue red and yellow heat shrink butt connectors

Heat shrink connectors work by joining electrical wires together.  The most popular option in the automotive industry is the heat shrink butt connector. They act as a form of tubing that connects two wires and are available in a range of sizes and colours.  The most common example is constructed with a dual wall design with shrinkable inner and outer layers.  When heat is applied to the connector they create a water-tight seal.

Heat Shrink Butt Connectors Colour Guide

  • White Connectors - Wire Size 0.25-0.34mm² (24-26AWG)
  • Red Connectors - Wire Size 0.5-1.0mm² (18-22AWG)
  • Blue Connectors - Wire Size 1.5-2.5mm² (14-16AWG)
  • Yellow Connectors - Wire Size 4-6mm² (10-12AWG)

 

Is Heat Shrink Tubing Waterproof?

Yes, once applied correctly heat shrink tubing is waterproof.  It will protect against most liquids, even corrosive substances, and keep out other types of environmental contaminants such as dust and dirt.  Once fitted securely in place it provides an excellent protective barrier.

Can You Use a Hair Dryer to Shrink Heat Shrink Tubing?

You should use a heat gun to shrink heat shrink tubing into place.  However, if you are feeling like the A-Team you could go ahead and use a hairdryer.  It will take a lot longer but you should get there in the end.  A heat gun gives much greater control than a hairdryer.  It does the job a lot more quickly and will result in a more even, accurate and secure fit.  So, the answer is yes - you can use a hairdryer if you're stuck, but you should really be using a heat gun.  

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Is It Ok To Cut Heat Shrink Tubing?

Yes, it can be cut.  Heat shrink tubing should be cut to size so that you use the correct length for the job at hand.  It is easy to cut and should be cut with a standard pair of scissors.  If scissors aren't doing the job you can use some wire cutters.  Measure the length you need before cutting.  As the saying goes - measure twice, cut once.

 

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