Final answer:
Drain wires in fire alarm and instrumentation cable are used to provide grounding for the cable, which helps reduce electromagnetic interference and increases safety.
Step-by-step explanation:
The correct answer to the question about the role of drain wires in fire alarm and instrumentation cable is that they are used to provide grounding for the cable. This makes option 1) the correct choice. The purpose of these drain wires is essentially to create a low-resistance path to ground, which can help in reducing electromagnetic interference by offering a route for it to follow and disperse, as well as augmenting safety.
Drain wires do not carry the signal or provide insulation; instead, they are incorporated into cabling systems to improve the electromagnetic compatibility (EMC) of the signal carried by the cable by reducing noise and potential interference.
The three-wire system, which includes live/hot, neutral, and earth/ground wires, likewise utilizes grounding to protect against shock and thermal hazards. The neutral wire and the case of the appliance are connected to ground to ensure they are at zero volts relative to earth, making them safe to touch and offering an alternate path for current in case of a fault. The safety mechanisms like ground fault circuit interrupters (GFCI) or fuses aim to prevent shock or thermal overload by interrupting the circuit under hazardous conditions.