Which statement is true regarding drain wires in fire alarm and instrumentation cables?

In fire alarm and instrumentation cables, the presence of drain wires plays a crucial role in managing electrical noise and providing a path for any induced or stray electrical currents. When the statement indicates that only one end of the drain wire is typically grounded, it reflects standard practice in electrical installations.

Grounding only one end of the drain wire helps to minimize ground loops, which can create interference and degrade the performance of the alarm system. This practice ensures that the drain wire can perform its function effectively without introducing unwanted currents that can occur with a two-ground configuration. By grounding just one end, designers and electricians can maintain signal integrity while providing a means for any stray voltages to safely dissipate.

In contrast, the other statements do not align with typical practices. For instance, generally both ends being grounded could lead to potential ground loops; indicating that drain wires are not required in fire alarm cables dismisses their importance in proper signal management; and stating they are insulated from each other would misrepresent their purpose, as they need to be in contact with the shield to carry away interference. This understanding of how drain wires function in fire alarm cables is crucial for maintaining system reliability and integrity.