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How to Choose and Correctly Measure Tubing

When shopping for heatshrink tubing, both the appropriate type of shrink and the right fit truly matter.

Heatshrink can play several roles in wire coverage after it is heated onto harnesses or individual cables. It can be shrunk into place to add abrasion protection, bundle cables and wires, color code, make connections, offer corrosion protection, provide chemical resistance, give flame retardancy, insulate, mark wires, resist moisture, offer mechanical protection, be used for splicing, provide strain relief, reinforce wires, and add weather sealing. Braided sleeving can additionally be paired with heatshrink for a finishing touch to terminate wires and cables.  

About the Heatshrink Categories

There are numerous applications where heatshrink tubing is helpful, including automotive, audio/visual, aviation, communications, and others. Categories include:

2:1 Polyolefin Shrinkflex Shrinktubing

This type is best for everyday applications, such as for bundling wire harnesses, in automotive wiring systems, for electrical insulation, to repair cables, in boat wiring to protect against saltwater and moisture, for sealing and waterproofing, to color code, within electronics, and for mechanical protection. ShrinkFlex® polyolefin tubing operates effectively in electrical and electronic applications indoors, outdoors, in harsh environments, for chemical resistance, or to resist abrasion. Aerospace, automotive, and marine applications are where this type is frequently found. There is also a glossy variety of thin-walled ShrinkFlex® that can provide a visually appealing backdrop for heatshrink printed logos.  Heatshrink made of PVC can protect wires or hoses out in the elements or exposed to abrasion or chemicals. Automotive or motorcycle cables and hoses benefit from this heatshrink variety.

3:1 Fabric Shrinkflex Shrinktubing

Hoses, pipes, and harnesses located in extreme environments with an abundance of dirt, grime, and harsh weather conditions, is where abrasion resistant heatshrink may also be found. Fabric styles with polyolefin and polyester are typically flexible, and avoid trapping humidity, water, and heat. Even in elevated temperatures, fabric heatshrink tubing continues offering abrasion, chafing, and cut-through protections for rubber hoses , plastic pipes, and harnesses. Dual wall adhesive heatshrink develops a weather tight seal and snug fit thanks to an inner adhesive.

4:1 Adhesive Shrinkflex Shrinktubing
This type of  heatshrink takes security to the next level, with a glue lining that adheres tightly over wires and connectors. Environmentally sealed heatshrink works for outdoor electronics, automotive or marine wiring, in aerospace and aviation applications, within industrial equipment, and for telecommunications infrastructure.
 
2:1 Kynar Shrinkflex Shrinktubing

Engine compartments, mechanical assemblies, and other high friction environments are suitable for flame retardant heatshrink. Kynar® heat shrink tubing is resistant to high temperatures, chemicals, abrasion, and cut-through — and is best in plenum applications. Heatshrink made of Viton® is suitable for military and commercial aircraft to resist corrosive fluids, lubricants, fuels, acids, solvents, abrasion, impacts, and cut-through. When heatshrink is needed for flame retardant qualities to sustain in engine compartments, along with similar applications, Polytetrafluoroethylene (PTFE) heatshrink has strong dielectric strength, the lowest coefficient of friction of any polymer, and a maximum operating temperature of 500°F (260°C).

2:1 Shielding Shrinkflex Shrinktubing
Wires and cables exposed to electromagnetic interference (EMI) can use some extra shielding protection. This dual wall ShrinkFlex® is made with an EMI shielding conductive cloth covered with polyolefin that protects from abrasion and chemicals in tight spaces, even when challenged with mechanical stresses and vibrations.
4:1 Teflon Shrinkflex Shrinktubing

Many of the same materials in flame retardant heatshrink are additionally used in chemical fluid resistant heatshrink. Kynar®, Viton, and PTFE chemical fluid resistant heatshrink are among the ones that can withstand environments with fuel, and other corrosive fluids. Military and commercial aircrafts, chemical plants, and engine compartments may be where this type of heatshrink functions best.

How to Properly Size Heatshrink

If heatshrink is much larger than the wire and cable bundle, it can fall off and will not function as it was designed. It is necessary to measure a cable or wire’s diameter with some common tools: a caliper, ruler, or tape measure. A pen or pencil should also be handy to document the measurements taken.

And how are measurements taken? Using a caliper, the measuring jaw needs to be expanded around the end and each side of a wire or cable. The caliper’s jaw is then closed around the wire or cable’s thinnest section. If it is not uniformly sized, the cable or wire should be measured instead at the widest point. To obtain a diameter using a ruler or tape measure, the wire or cable is placed against the wire or harness. Should there be a connector on the end of the cable or wire, it needs to be measured at its widest point, where heatshrink will then be shrunk over it. Measurements are not necessary for areas where tubing is not going to be added. With any of the measuring methods, the  heatshrink size is chosen based on the largest diameter. The tubingshould be able to slide over the connector and then shrink tightly to the wire. It is important to have sufficient heatshrink length as well to generously cover the wire or cable, because the length of the tubing also reduces after it is heated. 

Why Shrink Ratio Is Important

The smallest cables and wires, however, ultimately lead to choosing the correct heat shrink tubing shrink ratio. The shrink ratio is the tubing size after it has been heated and shrunk down. Understanding shrink ratio is crucial because when the appropriate shrink ratio is used, the inner diameter covers the cable and connector, and properly shrinks to the smallest portion of the assembly.  Shrinkage is based on the ratio’s first number — the higher that is, the greater it will shrink onto the items it is covering.

Shrink ratios are as follows:

Shrinkflex Shrinktubing 2:1 Ratio

A 2-to-1 ratio shrinks to one-half of its pre-heated size.

Shrinkflex Shrinktubing 3:1 Ratio

A 3-to-1 ratio shrinks to one-third of its pre-heated size.

Shrinkflex Shrinktubing 4:1 Ratio

A 4-to-1 ratio shrinks to one-quarter of its pre-heated size.

A 6-to-1 ratio shrinks to one-sixth of its pre-heated size.

And how are measurements taken? Using a caliper, the measuring jaw needs to be expanded around the end and each side of a wire or cable. The caliper’s jaw is then closed around the wire or cable’s thinnest section. If it is not uniformly sized, the cable or wire should be measured instead at the widest point. To obtain a diameter using a ruler or tape measure, the wire or cable is placed against the wire or harness. Should there be a connector on the end of the cable or wire, it needs to be measured at its widest point, where heatshrink will then be shrunk over it. Measurements are not necessary for areas where tubing is not going to be added. With any of the measuring methods, the  heatshrink size is chosen based on the largest diameter. The tubing should be able to slide over the connector and then shrink tightly to the wire. It is important to have sufficient heatshrink length as well to generously cover the wire or cable, because the length of the tubing also reduces after it is heated.

Watch the step-by-step tutorial below from WireCare® for more about this topic.

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