What type of foil shielding is used on data cables?

Foil shielding is critical in reducing EMI and other crosstalk in any cable design. In twisted data cables, two types of tin foil may be used inside —aluminum foil or copper foil. Three methods are commonly used in a cable’s foil construction — longitudinal, diagonal and wrapped.

Longitudinal — The easiest and cheapest foil method is the longitudinal cable construction using either aluminum or copper foil. It offers the best electrical shield effectiveness and does not require additional production processing. However, when foil is used in the longitudinal way, it can be rather stiff so is not as effective after movement. For example, when you move it more than a few times, the foil will begin to crack.

Diagonal — To increase flexibility, one should use the foil in the diagonal method, which can be implemented in the twisting process. Like longitudinal, it does not require additional production processing. However, when used in the diagonal way, more shielding foil is required than in a longitudinal way so you will increase your foil consumption and thus costs. Finally, diagonal shielding is not as effective as longitudinal when it comes to shielding.

Wrapped — Wrapping the shield foil offers the highest flexibility but its shielding effectiveness is the worst of the three. It also adds cost in production for taping of the foil.

Shielding is not enough between the cable shield and the connector. Some copper — either bare copper or tin copper — is necessary over the shielding foil. This copper can be designed into the cable in two ways, either as an indirect core or through copper braiding. Longer braids are less expensive and fast and easy to strip. However, they provide reduced attenuation and poor flexibility and service life, especially in moving applications. Shorter braids, on the other hand, are better for long service life on permanently moving applications, such as those in cable tracks. They offer higher attenuation than short braids. However, they have an upfront higher cost and are harder to strip.

This material was edited from a webinar presentation by Helukabel’s Horst Messerer, Product & Sales Manager of Data, Network & Bus Technology. Download the archived webinar for more on data, networks and bus technology.