Where is the drain wire typically terminated in an instrument system?

In an instrument system, the drain wire is typically terminated at the control cabinet. The primary function of the drain wire is to provide a path for any unwanted electrical noise or induced voltages that may affect the operation of sensitive instruments. By terminating the drain wire at the control cabinet, any electromagnetic interference is directed to a common ground point, allowing for effective shielding of the wiring and instruments from external electrical disturbances.

This termination strategy enhances the overall performance and reliability of the instrumentation system. Effective ground termination minimizes ground loops and potential differences in electrical potential that can lead to erroneous measurements or equipment malfunctions.

Other termination practices may not ensure the same level of noise protection or grounding efficacy. For example, terminating at just the conduit may not provide a direct path to ground, while terminating "at neither end" does not utilize the drain wire for its intended purpose. Lastly, terminating "at both ends" could potentially create a ground loop, which is counterproductive to preserving signal integrity.