Металл жабынды кабельдер: Электромагниттік кедергіден қорғау

Electric cable with metal jacket (shield) to prevent magnetic interference

A shielded cable or screened cable is an electrical cable that has a common conductive layer around its conductors for electromagnetic shielding. A longitudinal wire may be necessary with dielectric spiral foils to short out each turn. The shield should be electrically continuous to maximize effectiveness, including any cable splices. For high frequency signals (above a few megahertz), this extends to connectors and enclosures, also circumferentially: The cable shielding needs to be circumferentially connected to the enclosure, if any, through the connector or cable gland. Some types of shielded cable use the shield as the return path for the signal. As contrasting examples, coaxial cable does, whereas twinax cable does not. High voltage power cables with solid insulation are shielded to protect the cable insulation, people and equipment.

Different types of shielded cables are used based on the specific requirements of the application.

Foil shielded cables use a thin layer of aluminum foil for protection. They offer reasonable flexibility and are suitable for a wide range of applications. This type of shielding is often the most effective option for blocking EMI

Braided shielded cables have a wire mesh surrounding the internal wiring, offering robust protection against mechanical stress. They are more durable but less effective in preventing EMI compared to foil shields.

Combination shielded cables provide the durability of braided cables and the added protection against high levels of EMI. They are, however, heavier and less flexible than other types.

Spiral shielding uses helically wrapped metal strands to cover the cable’s conductors, offering good flexibility and coverage. However, they may not offer the same level of mechanical protection as braided shielding.

Serve shields, or served wire shields, consist of individual wires wrapped around the cable core. They provide good flexibility and ease of termination, suitable for applications requiring frequent cable movement.

Tape shields involve wrapping a conductive tape, often made of copper, around the cable. This type of shielding is used in high voltage power cables to prevent electrical interference.

Screen shields are similar to foil shields but often use a woven screen mesh to provide additional protection. They are commonly used in high frequency applications where both EMI shielding and physical durability are required.

The use of shielded cables in security systems provides some protection from power frequency and radio frequency interference, reducing the number of false alarms being generated. The best practice is to keep data or signal cables physically separated by at least 3 inches (75mm) from 'heavy' power circuits which are in parallel. Analog signal cable used in professional audio applications is usually shielded twisted pair cable terminated in XLR connectors. The twisted pair carries the signal in a balanced audio configuration. The audio multicore cable laid from the stage to the mixing console is also shielded. Consumers use screened copper wire with one central conductor in an unbalanced configuration.

The best way to wire shielded cables for screening is to ground the shield at both ends of the cable. Traditionally there existed a rule of thumb to ground only the source end of the shield to avoid ground loops. Best practice is to ground at both ends, but there is a possibility of ground loops. In airplanes, special cable is used with both an outer shield to protect against lightning and an inner shield grounded at one end to eliminate hum from the 400 Hz power system.