Mitsubishi TH-N12KP Thermal Relay for FA Series

Mitsubishi TH-N12KP Thermal Relay for FA Series

In modern industrial automation, the reliability of a control system is only as strong as the protection built into each layer of its architecture. The Mitsubishi TH-N12KP thermal overload relay is engineered to serve as a critical safeguard within the FA Series control platform, providing precise motor current monitoring and trip protection that integrates seamlessly across the control layer, I/O layer, power layer, and field device layer. Rather than functioning as a standalone component, the TH-N12KP is designed to operate as a coordinated element within a complete Mitsubishi FA system architecture, ensuring consistent protection logic, predictable response behavior, and long-term operational stability across the entire installation.

The TH-N12KP is a bimetallic thermal overload relay rated for use with Mitsubishi magnetic contactors in the N-series lineup. Its trip current range is factory-calibrated to match the thermal characteristics of standard three-phase induction motors, making it suitable for continuous-duty applications in manufacturing lines, process control panels, pump stations, compressor systems, and conveyor drives. The relay’s manual and automatic reset modes allow engineers to configure the protection response according to the criticality of the driven load, supporting both attended and unattended operational environments.

Product Specification Table

System Compatibility Notes

The TH-N12KP achieves its highest value when deployed as part of a coordinated Mitsubishi FA architecture. In a typical motor control center (MCC) or automation panel, the relay works in direct combination with the Mitsubishi N12 or N18 magnetic contactor, forming a complete motor starter assembly that is mechanically and electrically matched for optimal trip coordination. The contactor’s coil control signal originates from a Mitsubishi FX5U programmable logic controller or a Q06HCPU CPU module in larger QCPU-based systems, where the PLC output module — such as the QY10 transistor output module — drives the contactor coil through a 24 VDC control circuit.

On the input side, the TH-N12KP’s auxiliary NC contact feeds back a trip signal to a QX40 DC input module, allowing the PLC program to detect overload conditions in real time and execute protective logic — including alarm annunciation, drive inhibit, and event logging — without operator intervention. This closed-loop protection architecture eliminates the risk of undetected motor failures and supports the system’s overall fault tolerance strategy.

For systems requiring network-level diagnostics, the control panel may incorporate a QJ71E71-100 Ethernet interface module to transmit motor status and trip history to a SCADA or MES platform, enabling predictive maintenance workflows based on thermal trip frequency and reset patterns. Power to the control panel is supplied through a Q64P power supply module, which provides stable 5 VDC and 24 VDC rails to the QCPU backplane and I/O modules, ensuring that protection logic remains active even during transient load events on the main power bus.

Operator visibility is maintained through a Mitsubishi GOT2000 series HMI, where motor running status, overload trip events, and reset commands can be displayed and acknowledged from a centralized touchscreen interface. In variable-speed drive applications, the TH-N12KP may be installed on the line-side of a Mitsubishi FR-D720S inverter drive, providing upstream thermal protection independent of the drive’s internal electronic overload function — a dual-layer protection strategy recommended for high-availability process lines.

Terminal wiring within the control cabinet is organized using Mitsubishi-compatible DIN rail terminal blocks, and the overall panel layout follows IEC 61439 guidelines for low-voltage switchgear assemblies. This structured approach to panel design ensures that the TH-N12KP and its associated components can be inspected, tested, and replaced efficiently during scheduled maintenance windows, minimizing unplanned downtime across the production facility.

Industrial Application Notes

The TH-N12KP is deployed across a wide range of industrial sectors where motor protection is a fundamental requirement of the control architecture. In manufacturing and assembly lines, the relay protects conveyor motors, robotic axis drives, and pneumatic compressor motors from sustained overload conditions caused by mechanical jams, product accumulation, or drive belt failures. Its fast-response bimetallic element ensures that motor winding temperatures remain within safe limits even during repeated start-stop cycles.

In water treatment and pumping stations, the TH-N12KP is installed on submersible pump starters and surface-mounted centrifugal pump panels, where phase loss protection is particularly critical due to the risk of single-phasing caused by remote power distribution faults. The relay’s built-in phase loss sensitivity provides an additional layer of protection beyond what is available from standard fuse protection alone.

In power generation and electrical substation auxiliary systems, the relay protects cooling fan motors, oil pump motors, and battery room ventilation systems — loads that must remain operational during grid disturbances and emergency conditions. The TH-N12KP’s stable trip characteristics across a wide ambient temperature range make it suitable for outdoor switchgear enclosures and substation control buildings.

In petrochemical and process industries, the relay is used in hazardous area control panels (in conjunction with appropriate enclosure ratings) to protect agitator motors, transfer pump drives, and heat exchanger fan motors. Its manual reset mode is preferred in these environments to ensure that a qualified technician physically inspects the motor and driven equipment before restarting after a trip event.

In metallurgical and mining applications, the TH-N12KP protects crusher drive motors, conveyor belt drives, and ventilation fan motors operating under high-inertia, high-ambient-temperature conditions. The relay’s adjustable current setting allows site engineers to fine-tune the trip threshold to match the actual full-load current of each motor, reducing nuisance trips while maintaining effective overload protection.

Product Compatibility FAQ

Q1: Is the TH-N12KP compatible with all Mitsubishi N-series contactors, and can it be used with third-party contactors?
The TH-N12KP is designed for direct mechanical and electrical mounting with Mitsubishi N-series contactors, specifically the N10, N12, and N18 frame sizes. Direct mounting ensures correct current path alignment and eliminates the need for separate mounting adapters. While the relay’s auxiliary contacts can be wired into any control circuit, direct mounting to non-Mitsubishi contactors is not supported and may compromise the mechanical integrity of the assembly. For system consistency and warranty compliance, it is recommended to use the TH-N12KP exclusively within a Mitsubishi FA Series motor starter configuration.

Q2: How does the TH-N12KP integrate with a Mitsubishi PLC-based control system for remote trip monitoring?
The TH-N12KP provides a 1 NO + 1 NC auxiliary contact output that can be wired directly to a Mitsubishi QX40 or FX5U digital input module. The NC contact is typically wired in series with the contactor coil control circuit to provide hardwired trip interlock, while the NO contact provides a discrete trip signal to the PLC input for software-based alarm and logging functions. This dual-path integration ensures that motor protection is maintained even in the event of a PLC program fault, and that trip events are captured in the control system’s event log for maintenance analysis. No additional interface modules or signal converters are required for this integration.

Q3: What does the warranty terms confirmed during quotation cover, and what is the recommended maintenance interval for the TH-N12KP in continuous-duty applications?
The TH-N12KP is supplied with a warranty terms confirmed during quotation covering manufacturing defects in materials and workmanship under normal operating conditions. The warranty period begins from the date of shipment. For continuous-duty applications, it is recommended to inspect the relay’s current setting dial, reset mechanism, and auxiliary contact terminals at 12-month intervals or during scheduled panel shutdowns. The bimetallic element does not require calibration under normal service conditions, but relays that have experienced multiple trip events within a short period should be tested for trip accuracy using a relay test set. Replacement units are available from ZYPLC stock with short lead times to support planned maintenance programs.