Do You Need a Shielded Cable?
Posted 11 November 2014 5:00 AM by admin
Types of Shields used by New England Wire Technologies
The three most common shield types used by NEWT for multiconductor cable are braid, spiral, and foil. A braided shield is made of interwoven conductive wire. A braid can be manufactured using a wide variety of materials and wire sizes and can be applied over an extensive range of cable diameters. A spiral shield is made of conductive wire helically wrapped over the core. As with a braid, a variety of materials and wire sizes can be used however spiral shields are generally limited to small or mid-sized cables in order to achieve high coverage. A foil shield is a metallic foil helically wrapped around the cable with overlap. A variety of foil options can be utilized however most common is aluminum laminated with a polyester backing. Variations or combinations of the standard types are often used to provide a custom solution to a particular application.
In addition to wire and foil based shielding options, we also manufacture with semi-conductive tapes, coatings or extruded layers. These are typically used in conjunction with wire based shields and do provide additional shielding however these materials are most often employed to create low-noise or corona resistant high voltage cables.
So Which Shield Type is best?
The ideal shielding method for any application depends on many factors and each option has advantages and disadvantages. Shielding effectiveness at low frequencies is largely influenced by resistance. Therefore wire based shields such as spirals and braids are ideal. At high frequencies coverage becomes primary factor making 100% coverage foil shields the most effective option. At mid-range frequencies both resistance and coverage are influential so a high coverage braid is typically used.
While shielding effectiveness is often the primary goal other impacts of shielding must be considered. The effect on cable flexibility, flex life, diameter, weight and cost may influence the shield selection. Also, in order to get the full benefit of shielding the shield must be grounded properly so the means of termination can play a role in shield selection.
Variations or combinations of the standard shield types are often used to maximize shielding effectiveness for a given application. For example stacking a foil and braid will provide a shield with 100% coverage and low resistance making it effective from low to high frequencies.
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