How does a shield drain wire function in shielded control cables?

How does a shield drain wire function in shielded control cables?

• A. The drain wire is grounded to carry away EMI from the shield, helping maintain signal integrity.
• B. It carries main current to the load.
• C. It provides structural support.
• D. It insulates the shield from ground.

Answer: (A)

Shielded control cables are designed so that interference picked up by the outer shield is diverted away from the inner signal conductors. The drain wire provides a direct, low-impedance path to ground for that interference current. By grounding the drain wire (and thus the shield), EMI is carried away to earth, helping maintain signal integrity and reduce noise in the controlled circuit. This isn't used to carry the main load current—that's the conductors inside the cable—nor does it provide structural support or insulate the shield from ground. Its job is to connect the shield to the equipment ground so any EMI on the shield is drained away rather than affecting the signal.

Shielded control cables are designed so that interference picked up by the outer shield is diverted away from the inner signal conductors. The drain wire provides a direct, low-impedance path to ground for that interference current. By grounding the drain wire (and thus the shield), EMI is carried away to earth, helping maintain signal integrity and reduce noise in the controlled circuit. This isn't used to carry the main load current—that's the conductors inside the cable—nor does it provide structural support or insulate the shield from ground. Its job is to connect the shield to the equipment ground so any EMI on the shield is drained away rather than affecting the signal.