A programmable logic controller (PLC) is being used to control a series of pumps. The input module receives a 24 V DC signal from a pressure switch, and the output module actuates a 120 V AC contactor coil. What type of isolation is typically employed in the output module to protect the PLC's internal low-voltage electronics from the higher voltage of the contactor coil?

Question: A programmable logic controller (PLC) is being used to control a series of pumps. The input module receives a 24 V DC signal from a pressure switch, and the output module actuates a 120 V AC contactor coil. What type of isolation is typically employed in the output module to protect the PLC's internal low-voltage electronics from the higher voltage of the contactor coil?

Answer options:

• Resistive isolation.
• Capacitive isolation. ✅ Relay (electromechanical) isolation or opto-isolation.
• Inductive isolation.

Correct answer: Relay (electromechanical) isolation or opto-isolation.

Explanation: PLC output modules that connect to higher voltage/current loads like contactor coils typically use electrically isolated components to protect the sensitive internal low-voltage logic circuitry. This is commonly achieved through either electromechanical relays (which provide physical separation) or opto-isolators (which use light to transmit signals across an insulating barrier), both effectively isolating the control voltage from the load voltage.