How do the three common types of shielded cables work

Three basic types of shielding for electromagnetic interference (EMI) in cables

1. Braided copper and similar metal strands,

2. Spiral shielding layer

3. Foil and tape shield.

1. The metal braid shielding layer can be made of bare, tin-plated or silver-plated copper, steel or twisted metal wire. They are woven like fabric braids. The shielding effect is proportional to the coverage of the braided layer on the wire. Most braided shields provide 75% to 85% coverage. A higher percentage is possible, but can be very expensive. While it is theoretically possible to achieve 100% coverage, this is not a practical goal. Braided shielding is usually supplemented with foil shielding to increase shielding coverage and thereby improve EMI performance. Braided shielding has excellent low frequency performance, while foil shielding provides higher frequency shielding. Because of its numerous performance advantages, braided shields are often used in military and industrial applications. In addition to EMI shielding, the braided layer can also provide higher mechanical strength, flexibility and physical protection for the cable.

2. The spiral shield is a variant of the braided shield. They are formed from shielded metal bundles, constructed by winding the shielding material around a conductor in one direction and then in the opposite direction in a second direction. The shielding lines are not intertwined. They cost less than braided shielding and can achieve 95% coverage, but due to frequency limitations, they can only be found in audio applications.

3. Foil and tape

The difference between foil and tape is arbitrary and usually depends on the manufacturer. The metal layer of foil may be thinner than tape, but this is not always the case. Foil and tape are usually provided in the form of a metal layer such as aluminum or copper, located on a substrate called a tape made of mylar, polyester, or similar material. They are sometimes called foil strips, which adds to the confusion. These shielding layers can be either longitudinally or spirally wound around the cable. Low inductance for longitudinal winding. While braided shielding is typically used for heavy-duty cables with multiple wires and wire pairs, foil and tape are typically used for single twisted pairs or thin cables. Various types of shielding layers are often used in combination.

VFD cable shielding layer

VFD cables are complex components. They include wires for transmitting high-power pulse width modulation (PWM) signals used to drive the motor, separate brake cables, induction motors, and environmental parameters, among others. They use a variety of shielding materials, including braids, foils and tape. In addition to EMI protection, they require high voltage electrical isolation (from 600 to 15kV). Due to the nature of PWM drivers, longer cables may withstand larger voltage spikes and require stronger insulation and shielding. There are many manufacturers of VFD systems, and each manufacturer has a preferred cable structure

Shielded cable

Twisted pair cables for Ethernet, also known as class cables, are usually shielded by EMI. Ethernet is used in a wide range of environments, from relatively mild office or residential locations to challenging industrial environments. As a result, the shielding structures associated with class cables are equally extensive. The ISO/IEC 11801 standard defines standard acronyms to describe various types of cable shielding structures.

Acronyms usually have two parts: before and after 'slash'. The first code represents the shielding of the entire cable, and the second code represents the shielding of a single twisted pair. Examples include:

1.F/UTP - Foil cable/Unshielded Twisted pair These cables typically include four pairs of unshielded twisted pair for 10GBaseT applications.

2.S/UTP - Shielded cable/unshielded twisted pair.

3.SFTP - Shielded and foil twisted pair for maximum EMI shielding.

4.SF/UTP - Shielded and foiled cables/unshielded twisted pair are common general-purpose Ethernet cables.

5.S/FTP - Shielded cable/foil twisted pair minimizes crosstalk between twisted pairs.

6.F/FTP - Foil cable/foil twisted pair is another common configuration for 10GBaseT applications.

7.U/FTP - Unshielded cable/foil twisted pair is another configuration for 10 GBaseT applications.

8.U/UTP (UTP) - Unshielded cable/unshielded twisted pair for environments that do not consider EMI.