Braided Cables | Screened Cable

For greater protection cables can be shielded by the addition of a foil screen or wire mesh using the faraday cage principal to reduce electrical noise and electromagnet radiation either to or from other components within the cable or external sources. The addition of a collective cable shield over a group of wires or twisted pairs is referred to as cable screening or cable braiding.

In all cases for the cable screen to work they must be physically grounded usually by the addition of a grounding wire called a drain-wire inserted into the lay of the cable.

It is also possible to use a semi conducting elastomer in combination with any of the wire based constructions.

The choice to which form of cable shielding to use will depend on the cables application, operational environment and importance of the data or signals being transmitted through the cable.

It is still a cost against benefit decision particularly when specifying a wire construction were you need to decide on a lapped screen (generally used when Coiling the cable) or braid style of construction.

The level of coverage deemed necessary to give the level of protection required is also determined by the importance of the data or signals being transmitted.

CDC Ltd can advise on all of these aspects of cable screening and cable design, performance and cost as part of our custom cable service.

In today’s world almost everyone and everything comes into contact with an increasing level of sophisticated electrical and electronic equipment that generates EMI (electromagnetic interference) or EMP (electromagnetic pulses) to the extent that legislation now exists to ensure that wherever possible, all equipment and ancillary components are compliant with EMC (electromagnetic compatibility) rules. The objective of EMC is to minimise the source of EMI and EMP and to protect from interference through good product design.

Consequently, this requirement applies to an increasing range of cables were the application or operational environment means that they are likely to be a source of interference or may require protection from interference. Fortunately, within the cable industry there exists a wide range of solutions to address a broad range of frequency bandwidths from simple cross-talk to nuclear EMP cable shields. However, this does require that each cable must be designed to meet its obligations with respect to EMC whilst retaining its physical and mechanical performance properties. This is where we come in.

The Solutions range from a cost effective yet simple aluminium or copper foil tape to multiple optimised cable braids coupled with the use of a variety of alternative ferro-magnetic wraps or different metallic wires. However, the more sophisticated the solution the higher the cost and this is where we can help to advise and suggest different methods for the customer to balance the cost against the cables’ performance within the required application.

As a general guide a simple aluminium foil will provide an electrostatic screening at a low cost without adding an extra cable manufacturing process. The next option is a helically lapped copper screen (spiral screen or lapped screen) which is ideal for individual core or twisted pair screening. It can also be employed an overall cable screen were the cables’ flexibility is important. This is an ideal form of cable screening where flexibility would be required for use in a retractable cable.

Moving down the cable screening hierarchy, we now come to the traditional (woven) cable braid wire screen, using a range of wire types from plain to tinned copper, to silver, to textile braids and Kevlar braids. This form of cable braiding offers endless possibilities relating to the % coverage required for example 50% to 100% which in turn is determined by the importance of the signals being transmitted. As a CDC Ltd improved cable performance suggestion, we tend to suggest multiple fine wires leading to a more flexible cable whilst giving a high coverage factor.

From here the design moves onto a combination of multiple braid layers with additional layers of a metallised foil between each braid. These combinations will be dictated by the severity of the increasing levels of EMI from low with a single braid screen, through high and severe EMI levels up to the severest levels of EMP which could contain at least 3 separate cable braiding layers and also individual layers of moralised tapes.

As you can see, cable shielding is complex. However, by involving the cable manufacturer in the final design of your cable, it will result in the provision of a custom cable that will meet its EMC obligations.