SHEATHING materials for cables

Sheathing

Although the sheath (or jacket) offers isolation from the earth-plane for any shielding of the cable, it is primarily used to provide mechanical protection from a wide variety of hazards. There is a wide range of materials that can be used for sheathing cables, all with their own advantages and limitations.
Abrasion Measures the rugged properties of a material. Typically softer, more flexible sheaths will exhibit a high degree of abrasion loss. HFI 260 when used as a sheath exhibits possibly the best abrasion resistance.

Corrosivity

Under fire conditions, many materials such as FEP, although very good in fire, will release toxic and corrosive gasses once they eventually ignite. Corrosive gasses can damage sensitive equipment such as circuit-boards and consideration to this should be given when installing cable in potentially sensitive areas. HFS 80 is one such example.

Flammability

The degree to which the sheath will burn and/or spread a fire once ignited. Most materials used by Habia will self-extinguish once the flame source has been removed. With many different national and international fire standards in use, Habia recommends IEC 60331 and IEC 60332 (in applicable parts) as these test the completed cables and are therefore more truely representative of the application.
The other test that is commonly requested is flammability to UL 94. This method tests a small sample of the sheath material and does not assess the overall cable construction.
The flame retardancy of many sheaths such as TPS 100 can be improved by flame retardant (FR) additives, however these do affect other material properties.

Flexibility

There are two key aspects to this. Flexibility is the degree to which a cable can bend; flex-life is the frequency over which a cable can be flexed without breaking. Some materials may have poor flexibility, but are actually so strong that they can exhibit a very good flex-life. MPR 105 is an example of both good flexibility and flex-life.

Fuels and oils

Many fluids will actively break-down the chemical bonds of the sheath. This effect is often magnified when the fluids are at temperature (such as an engine-bay). Cross-linked materials such as TPS 125 XL are particularly good at resisting damage from chemicals.

Radiation

As with fuels and oils, continued exposure to radiation will break-down plastic. Many different measurement scales exist, however the most common are Rads and Grays. Habia will quote the Total Integrated Dose (TID) in Grays (Gy) unless otherwise specified. HFS 100 is an example of a highly radiation tolerant sheath.

Smoke generation

This refers to the level of smoke that is generated by a material under fire conditions. This is of key importance where visibility must not be impeded (for example: the route to an exit). As with flexibility and flex-life there is no link between smoke corrosivity and smoke generation, so whilst materials such as FEP might be very corrosive, they actually generate very little smoke. HFS 107 XL is one of the best examples of a low smoke-generation sheath.

Water resistance

Where the sheath is concerned, this is the degree to which water can either be absorbed by the sheath (swelling its size) or permeate through it, flooding the cable interstices and allowing water to track back up to the connector. Habia’s TPU 90 is one of the best examples of a water resistant sheath.

Zero halogen

The other side of smoke corrosivity, halogen content refers to the toxic gasses that can be emitted by the sheath under fire conditions. Halogens can affect health and therefore halogen free cables should be installed in areas of high foot-traffic and/or enclosed spaces. HFS 80 is one of the best zero halogen sheath materials.