How to Specify Shielded Cable

Industrial applications are typically electrically noisy environments. Electrical noise, either radiated or conducted as electromagnetic interference (EMI), can seriously disrupt the proper operation of other equipment. Insulation protects a cable mechanically from scrapes, abrasion, moisture, and spills, but insulation is transparent to electromagnetic energy and offers no protection. Shielding is needed to combat the effects of EMI.

Cables come with various degrees of shielding that offer different levels of effectiveness. The amount of shielding required depends on several factors, including the electrical environment in which the cable is used, the cost of the cable (why pay for more shielding than you need?), and issues like cable diameter, weight, and flexibility.

There are two types of shielding typically used for cables: foil and braid:

Most shielded cables are shielded by metal braid, which is soft and durable, but the density of the braid will make the shielding effect worse, and the braid way will make the shielding current less uniform, so the anti-magnetic field efficiency is 5-30db lower than that of the foil shielded cable. In addition, at high frequency, the ratio of interstitial space to the wavelength of the braided layer becomes larger, which further reduces the shielding efficiency. In this case, shielded cables at key locations should be double or even triple shielded cables in order to improve the coverage provided by the braided layer.

The cable with thin aluminum foil shielding layer can provide almost 100% coverage, so it has better electric field shielding effect. It is not as strong as braided shielded cables, and it is difficult to end (360°).

The better-shielded cable is composed of an aluminum foil layer and braided layer. The braided layer can solve the continuous end connection of 360°, while the metal foil layer can cover the gap of the braided layer.

Here are a few things to consider when choosing a cable:

1:Make sure you have a cable with sufficient shielding for the application’s needs. In moderately noisy environments, a foil alone may provide adequate protection. In noisier environments, consider braids or foil-braid combinations.

2:Use a cable suited to the application. Cables that experience repeated flexing typically use a spiral-wrapped shield rather than a braid. Avoid foil-only shielding on flex cables since continuous flexing can tear the foil.

3:Make sure the equipment to which the cable is connected is properly grounded. Use an earth ground wherever possible and check the connection between the ground point and the equipment. Noise elimination depends on a low-resistance path to ground.

4:Most connector designs allow full 360-degree termination of the shield. Make sure the connector offers shielding effectiveness equal to that of the cable.

So, high-quality cables should be matched with high-quality connectors. A shielded system is only as good as its weakest component; a high-quality cable is defeated by a low-quality connector. Similarly, a great connector can’t do anything to improve a poor cable.