Cable Core - Insulation Needs

[Ganimedes Reveley]

Cable Core - Insulation Needs

Insulation is necessary to provide electrical isolation between the conductor and the earth-plane.  The choice of insulation can also have a significant impact on the overall performance of the cable.  There is a wide range of materials that can be used for insulation;  some can also be used for sheathing cables, all have their own advantages and limitations.

Abrasion
Measures the rugged properties of a material. High abrasion resistance is ideal in dynamic cables where cores are required to move in relation to one other, and to any shield as the cable is flexed. LSI 155 has excellent  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. HFI 140 is a good example of low corrosivity. 

Flammability
The degree to which the insulation 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 truly 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. PTFE is one of the best flame retardant insulations. 

Flexibility
There are two key aspects to this. Flexibility is the degree to which a cable can bend whilst 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. Although not the most flexible by any means, ETFE is ideal as insulation for flexible cables as its combines abrasion resistance and flex-life. 

Fuels and oils
Many fluids will actively break-down the chemical bonds of the insulation. This effect is often magnified when the fluids are at temperature (such as an engine-bay). PFA is amongst the best insulation materials for fuel and oil resistance as it is able to operate in fluids at very high temperatures. 

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. HFI 260 is the best example of a highly radiation tolerant insulation. 

Smoke
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, although FEP is one of the most corrosive materials, it is also one of the best examples of a low smoke-generation insulation. 

Water
Where the insulation is concerned, this is the degree to which water can permeate through it, creating an electrical path from conductor to earth (known as arc tracking). ETFE is again one of the best materials for use  in water. 

Zero halogen
The other side of smoke corrosivity, halogen content refers to the toxic gasses that can be emitted 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. HFI 140 is one of the best examples of a zero halogen insulation material.

source from habia cable