GE Multilin 239-RTD-AN Motor Protection Relay with 8 RTD Inputs and 6 Output Relays

Description

The 239-RTD-AN​ is an RTD-based temperature monitoring and motor protection relay manufactured by GE Multilin, designed to watch up to eight resistance-temperature detectors and turn their readings into alarm, trip, and analog-output actions before heat damages a motor, generator, pump, or fan. It is the kind of device that sits quietly in a panel for years and then earns its keep in about three seconds — by opening a contactor before a winding hotspot becomes a rewind.

What separates the 239-RTD-AN​ from a simple temperature transmitter is the combination of density and decision-making. Eight RTD inputs share one DIN-rail-mounted housing, each converted by a 14-bit analog-to-digital converter at better than 5% accuracy; six programmable relays provide both alarm and trip contacts, while two 4–20 mA outputs carry temperature or alarm-state data to a controller or recorder. The front panel offers a scroll-key and LED array, with an optional 4-line LCD for local readout, and an RS-485 port speaks Modbus for integration with plant SCADA. The 239-RTD-AN​ is now discontinued and fully obsolete — GE declined support in 2017 — so the available units are new-surplus or tested legacy, and a migration path to the Multilin 650​ or 235​ belongs in any serious spare-parts plan.

Application Scenario

A water utility operates a bank of 2.2 MW vertical turbine pumps on a raw-water intake, each with six embedded winding RTDs and two bearing-temperature detectors. The original protection scheme used a stack of individual temperature switches, each with its own setpoint and its own contact — six devices per pump, no common alarm, and no way for the control room to see a temperature trend until a bearing failed. During a summer peak, one pump seized after a hotspot went unnoticed for two shifts; the rewind cost six figures and took the pump out of service for three weeks.

The utility replaced the switch stack with the 239-RTD-AN. All eight RTDs landed on one DIN-rail device: six winding points fed the trip logic, the two bearing points drove a staged alarm, and the two 4–20 mA outputs sent temperature data to the SCADA historian. The result was visible trending for the first time — operators could see a bearing heating up over days rather than hours — and the alarm contacts gave them warning while the pump was still saveable. Two years later the utility reports no thermal failures on the monitored pumps, and the maintenance team keeps a tested 239-RTD-AN​ on the shelf, justified by the single rewind it has already prevented.

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