In shielded cables, why is the drain wire typically bonded to ground at the equipment end?

In shielded cables, why is the drain wire typically bonded to ground at the equipment end?

• A. To carry main current to the device.
• B. To bond the drain wire to ground at the equipment end to carry EMI away.
• C. To hold the shield in place physically.
• D. To act as a data conductor.

Answer: (B)

The drain wire in a shielded cable serves as a convenient path to ground for interference currents that ride on the shield. By bonding this drain wire to equipment ground at the equipment end, any EMI picked up by the shield is diverted safely away from the signal conductors and into the earth/ground system. This keeps the shield at or near ground potential and reduces the chance that noise will couple into the protected circuitry, improving signal integrity. The drain wire is not meant to carry main current or data, and the purpose is specifically to drain EMI away rather than to provide power or a data path. Bonding at the equipment end helps prevent ground loops while still giving the shield an effective discharge route for interference.

The drain wire in a shielded cable serves as a convenient path to ground for interference currents that ride on the shield. By bonding this drain wire to equipment ground at the equipment end, any EMI picked up by the shield is diverted safely away from the signal conductors and into the earth/ground system. This keeps the shield at or near ground potential and reduces the chance that noise will couple into the protected circuitry, improving signal integrity. The drain wire is not meant to carry main current or data, and the purpose is specifically to drain EMI away rather than to provide power or a data path. Bonding at the equipment end helps prevent ground loops while still giving the shield an effective discharge route for interference.