IS230TNCIH4C Mark VIe | Replacement Current Input TB for GE

Description

Product Introduction

The transmitter shorted—just a 100 pressure transducer in the lube oil system. But it took out the entire common power bus on the TNCIH4, dropping all 16 analog inputs and tripping the turbine. That was a 40,000 lesson. The TCINH4C solves that problem: every channel has its own 100 mA fuse, so a single shorted transmitter takes out only its own channel—not the whole bus. I’ve been specifying these ever since.

GE’s IS230TNCIH4C is the termination assembly for the Mark VIe analog current input modules (like the PDOAH1A or PIOAH1A). It provides the physical interface between the 4-20 mA field instruments and the module—a 37-pin D-sub connector on one side and screw terminals on the other. Like the TNCIH4, the TNCIH4C has a common loop power bus: a single pair of terminals supplies 24 VDC to all 16 channels. What it adds is a 100 mA fast-acting fuse on every channel, protecting the module from short-circuit overcurrent events and isolating a failed instrument from the rest of the bus. The C revision adds improved ESD protection, more robust fuse holders, and a fuse-blown LED (red) per channel that illuminates when the fuse is open.

Key Technical Specifications

• Channel Count: 16 fused analog current inputs
• Input Type: 4-20 mA (loop-powered field instruments)
• Fusing: 100 mA fast-acting, per channel (field-replaceable)
• Burden Resistor: None (provided by the I/O module internally)
• Loop Power: Common 24 VDC bus with fused outputs to each channel
• Fuse-Blown Indicator: Red LED per channel (illuminates when fuse is open)
• Connector Type: 37-pin D-sub (female) for module connection
• Field Wiring: Screw terminals (0.5-2.5 mm² / 20-14 AWG)
• Loop Power Terminals: One “+” and one “–” terminal for 24 VDC supply
• Terminal Markings: Clearly labeled with channel numbers (1-16) and polarity (+/-)
• Mounting: DIN rail or panel mount
• Operating Temperature: –30 to +65 °C ambient

Quality Inspection Process (SOP Transparency)

This is what every IS230TNCIH4C goes through before it ships:

Incoming Verification: The OEM packing slip is matched against the shipping manifest. Visual inspection includes checking the GE holographic label, verifying the 37-pin D-sub connector is straight and has no bent pins, and examining the screw terminals for any signs of stripped threads or corrosion. We also inspect the fuses—they must be 100 mA fast-acting, properly seated in their holders, and the fuse-blown LED must be functional.

Live Functional Test: The TNCIH4C is installed in a test fixture with a Mark VIe analog input module (PDOAH1A). We connect a 24 VDC power supply to the common loop power terminals and verify that all 16 channels receive the 24 VDC supply through their fuses.

We then connect a loop-powered simulator (a Fluke 789 ProcessMeter configured in loop power mode) to each channel in sequence, injecting 4.00 mA, 12.00 mA, and 20.00 mA. We verify the module reads the expected current value.

For the fuse test, we short-circuit each channel (simulating a failed transmitter) and verify the 100 mA fuse blows within 1 second. The red LED for that channel must illuminate. We then replace the fuse with a new 100 mA fast-acting fuse and verify the channel returns to normal operation.

For the loop power distribution test, we measure the voltage at each channel’s field terminals—it must be the same as the common power supply voltage (24 VDC) minus the drop across the fuse (negligible, <0.5 V at 20 mA).

Electrical Parameters: A Fluke 1587 insulation tester measures isolation between the current inputs and the D-sub connector (the I/O module provides the isolation, but we verify the terminal block itself has no leakage). We look for >20 MΩ at 500 VDC. We also verify the continuity of the common loop power bus—resistance between the common terminal and each channel’s “+” terminal (with the fuse intact) must be <0.1 Ω.

Mechanical Inspection: Each screw terminal is tested by tightening and loosening it five times to ensure the threads are not stripped. The D-sub connector’s mating surface is inspected for any burrs or damage. The fuse holders are tested by inserting and removing fuses three times to ensure they grip properly.

Final QC & Packaging: The QC report lists the channel verification for all 16 channels, the fuse test results (all 16 fuses verified to blow and be replaceable), the loop power distribution test, and the isolation measurements. The terminal block goes into a new anti-static bag with a tamper-evident seal, then into a double-walled carton with foam inserts. A “QC Passed” label with the test date and technician’s ID goes on the outer box. All test data and photos are available on request.

Field Replacement Pitfalls

The TNCIH4C is a simple but effective terminal block. Here’s my field-tested list.

Fuse Replacement and Rating
The TNCIH4C uses 100 mA fast-acting fuses (GE part number 193X900-2 or equivalent). If you replace a blown fuse with a slow-blow fuse or a 250 mA fuse, the module won’t be protected. I saw a plant where a technician replaced a blown 100 mA fuse with a 250 mA slow-blow fuse—the next transmitter shorted and the 250 mA fuse didn’t blow, causing the common power bus to drop and all 16 channels to lose power. ❗ Use the correct fuse: 100 mA fast-acting, 250 V rating. Don’t substitute. The fuse spec is printed on the terminal block label.

Fuse-Blown LED Interpretation
The red LED on the TNCIH4C illuminates when the fuse is open. But it’s a passive indicator—it draws its power from the loop supply. If the loop supply is off or low, the LED won’t illuminate even if the fuse is blown. I had a plant where a fuse was blown, but the loop supply was turned off, so the LED didn’t illuminate. The technician assumed the channel was working and wasted an hour troubleshooting. ❗ The fuse-blown LED only works when the loop supply is powered. Always check the loop supply before trusting the LED.

Common Bus Voltage Drop with Fuses
The 100 mA fuses have a resistance of about 0.5 Ω each. At 20 mA per channel, the voltage drop across each fuse is 10 mV—negligible. But if a channel’s fuse is dirty (corroded contacts), the voltage drop can increase to 1-2 V, causing the instrument to underperform. I had a plant where a corroded fuse holder was dropping 1.5 V on channel 8, and the loop-powered transmitter was operating at the edge of its supply voltage. The fix was cleaning the fuse contacts. ❗ Keep the fuse holders clean. Use a contact cleaner if you see any discoloration.

Short-Circuit Response
The 100 mA fast-acting fuse is designed to blow within 1 second at 200 mA and within 10 ms at 1 A. If you have a transmitter that draws a short-duration inrush current (say, 150 mA for 50 ms), the fuse may not blow—it’s designed for sustained overcurrent. I had a plant where a transmitter had a 150 mA inrush for 100 ms at startup, and the fuse didn’t blow, but the module’s internal protection (which is faster than the fuse) tripped, causing the channel to fault. The fix was adding a soft-start circuit to the transmitter. ❗ The fuse protects against sustained overcurrent, not transient inrush. If you have transmitters with high inrush current, you may need a different protection scheme.

Common Bus Fusing vs. Per-Channel Fusing
The TNCIH4C has per-channel fuses, but the common bus itself is not fused. If the common bus is shorted (say, a wiring fault at the terminal block), there’s no protection—the entire bus will drop, and all 16 channels will lose power. I had a plant where a stray wire shorted the common bus “+” terminal to ground; all 16 channels dropped to 0 mA, and the turbine tripped. The fix was adding a 2 A fuse on the common bus input. ❗ The common bus is not fused by the terminal block. Add a 2 A fuse on the common power supply input to protect against bus shorts.

Get these five right and you’ll cut rework time by 90%.

New Original vs. Refurbished: Why It Matters

The TNCIH4C is a simple terminal block with fuses. Refurbishment risk is moderate.

New Original (New Surplus) means this unit came from GE’s production line, sealed in an ESD-safe bag. It has never been wired. The fuses are fresh—no damage, no corrosion. The fuse holders have pristine spring contacts. The screw terminals have fresh threads. The D-sub connector has pristine pins. The serial number traces directly to GE’s production database.

Refurbished risk: The biggest issue with refurbished TNCIH4C blocks is the fuse holders. They have spring contacts that weaken with repeated fuse insertion/removal. A refurbisher may have tested the fuses by inserting and removing them multiple times, weakening the contacts. A weak contact can cause an intermittent connection—the instrument works sometimes, then fails. I saw a refurbished TNCIH4C in a plant where channel 5 would occasionally lose its 4-20 mA signal; the fuse holder had a weak contact. The plant spent a day chasing the problem before replacing the terminal block. The refurbished block cost 250; the new surplus unit was 350. The day of troubleshooting cost $5,000.

Real cost: An intermittent 4-20 mA signal can cause a fuel flow measurement error, leading to a turbine derate or trip. The cost of a derate is thousands of dollars per day. A new surplus terminal block is cheap insurance.

What we provide: We include a photo of the OEM packing slip with the GE part number and serial number. The anti-static bag is sealed with a tamper-evident label. The QC test report lists the channel verification, the fuse test results, the loop power distribution test, and the isolation measurements. You get a 12-month warranty.

Pricing context: Our price sits 30-50% above refurbished alternatives but 20-40% below GE’s current factory list price.

Performance Benchmarks & Test Results

Measured during our QC test. Conditions: test fixture with a PDOAH1A analog input module, 24.0 VDC supply (Fluke 8845A), ambient 24 °C.

• Fuse Voltage Drop: At 4.00 mA: 0.02 V. At 12.00 mA: 0.06 V. At 20.00 mA: 0.10 V. Within the <0.5 V spec.
• Fuse Blow Time: With a 200 mA overcurrent, the fuse blew in 800 ms (within spec). With a 1 A overcurrent, the fuse blew in 8 ms (within spec).
• Fuse-Blown LED: With a blown fuse and 24 VDC loop supply, the red LED illuminated brightly. With 18 VDC supply, it was still visible (dim but functional).
• Common Power Bus Voltage: Applied 24.00 VDC at the common power terminals. Measured 23.90 VDC at the field terminals of channel 16 (the furthest from the supply) with all channels at 20 mA. Voltage drop: 0.10 V (including fuse drops).
• Current Measurement Accuracy: At 4.00 mA injected, the module read 4.001 mA. At 12.00 mA: 11.999 mA. At 20.00 mA: 20.002 mA. All within ±0.05% of the module’s accuracy spec.
• Common Bus Continuity (Fuse Intact): Resistance between the common “+” terminal and each channel’s “+” terminal: average 0.05 Ω. Range: 0.03-0.08 Ω.
• Common Bus Continuity (Fuse Blown): Open circuit (>10 MΩ).
• Insulation Resistance (Terminals to D-sub): Measured 50 MΩ at 500 VDC—well above the 10 MΩ minimum.
• Insulation Resistance (Channel to Channel): Measured >100 MΩ at 500 VDC.
• Thread Integrity: All screw terminals were tested with 5 cycles of tightening/loosening. No stripped threads.
• Fuse Holder Integrity: All 16 fuse holders were tested with 5 cycles of fuse insertion/removal. Contacts remained secure and made good electrical contact.
• MTBF (Published): GE’s datasheet lists 260,000 hours at 40 °C for the TNCIH4C. Based on field data, expect 15-20 years of service under normal conditions.

IS200EXIBG EXCITER BRIDGE INTER
IS200EXIBG1A
IS200EXIBG1AAA