GE IC694MDL930 | 8-Point Isolated Relay Output Module for RX3i – Field Service Notes

Description

Hard-Numbers: Technical Specifications

• Output Points: 8 isolated Form A (Normally Open) relay contacts
• Rated Voltage: 24VDC, 120/240VAC (nominal)
• Operating Voltage Range: 5–30VDC, 5–250VAC (47–63Hz)
• Output Current: 10mA minimum per point; 4A maximum resistive (5–250VAC, 5–30VDC); 2A pilot duty/lamp load
• Maximum Module Load: 20A total (UL installations); derates with ambient temperature
• Maximum Inrush: 5A
• Isolation Rating: 250VAC continuous (field to backplane, point to point); 1500VAC for 1 minute (dielectric withstand)
• Response Time: 15ms maximum (on/off)
• Backplane Power Draw: 6mA @ 5VDC + 70mA @ 24V relay bus (all outputs ON)
• Operating Temperature: 0°C to 60°C (+32°F to +140°F)
• Contact Life: 150,000 operations at 4A/24–120VAC; 50,000 operations at 4A/240VAC; 100,000 operations at 4A/24VDC; 1,000,000 at 0.1A
• Terminal Block: Integrated 20-screw terminal block (included with module)
• Hot Swap: Supported (per Emerson catalog)
• Wire Gauge: AWG #22 to #16 (two wires) or AWG #14 (one wire), 90°C rated copper

GE IC694MDL753

The Real-World Problem It Solves

When you’ve got a mix of 24VDC solenoid valves, 120VAC motor starters, and 240VAC contactor coils all landing on the same PLC rack, you don’t want shared commons creating ground loops or fault propagation. The MDL930 gives you eight independent dry contacts—each with its own return terminal. Wire channel 1 to a 24VDC source, channel 2 to 120VAC, channel 3 to 240VAC. No interaction between channels. A welded contact on one output doesn’t take down its neighbor.

Where you’ll typically find it:

• MCC retrofits where legacy motor starters at different voltages (120VAC, 240VAC, 24VDC) need to be controlled from a single I/O slot without interposing relays
• Packaged equipment skids (compressors, pump stations) with mixed-voltage field devices from multiple vendors
• Series 90-30 to RX3i migration projects where the same module can be deployed on either platform during the transition

Bottom line: It’s the low-density workhorse for mixed-voltage applications where point isolation trumps channel count. Eight outputs, eight separate commons, zero excuses.

Hardware Architecture & Under-the-Hood Logic

The MDL930 is a passive relay module with no onboard microprocessor. It receives 8 discrete output commands from the host CPU (RX3i or Series 90-30) over the backplane bus and energizes or de-energizes 8 electromechanical relay coils. Each relay is a Form A (SPST-NO) contact with its own dedicated coil and contact set. No shared commons—the return terminal for each output is isolated from all others.

Internal signal path:

1. CPU command → Backplane bus → Module interface latches 8 output bits
2. Driver circuit → Energizes relay coils individually → Relays close their Form A contacts
3. Field power → External AC/DC source → Through closed relay contact → Load
4. LED status → 8 individual numbered LEDs (1–8) → Indicate ON/OFF state of each output

The module draws relay coil power from the backplane’s 24V relay bus (70mA when all outputs ON), not from the external field power supply. The field power supply only powers the load devices. No diagnostic feedback to the CPU (unlike MDL916, which reports terminal block presence and over-temperature).

Key difference from MDL916: MDL930 has an integrated terminal block (included with module), while MDL916 requires a separate terminal block (IC694TBB032/IC694TBS032). MDL930 also has lower backplane power draw (6mA + 70mA vs. 300mA for MDL916) because it has half the relay count.

GE IC694MDL753

Field Service Pitfalls: What Rookies Get Wrong

Thermal Derating at High Ambient TemperaturesAt 55°C ambient, you cannot run all 8 outputs at 4A each. The derating curve in GFK-2705 shows that at 55°C, total module load current is limited to approximately 8A (roughly 1A per output average). Exceed this and you’ll overheat the relay coils, causing premature failure or intermittent operation.

• Field Rule: In hot cabinets (>40°C), derate your per-point load or reduce simultaneous ON outputs. Add forced ventilation. If you need 8 outputs at 4A each in a hot environment, use a solid-state output module (MDL754) instead of relays.

Contact Welding at 240VAC Inductive LoadsAt 240VAC with 4A inductive loads (contactor coils, solenoid valves), the contact life drops to only 50,000 operations without external suppression. That’s less than a year in a high-cycling application (once every 10 minutes = 50,000 cycles in ~350 days). The arc energy at 240VAC is significantly higher than at 120VAC.

• Quick Fix: Install RC snubbers across the load terminals for every 240VAC inductive load. A 0.1µF + 100Ω snubber can extend contact life from 50,000 to 200,000+ operations. For critical high-cycle applications, switch to a solid-state output module (MDL754) or use an interposing relay.

Minimum Load Threshold (10mA)The relay contacts require at least 10mA to maintain a clean, low-resistance connection. If you’re driving low-current loads like PLC inputs (typically 5mA at 24VDC), you’ll get intermittent contact closure and false “open” signals. This is a common issue when using relay outputs to signal other PLCs or DCS systems.

• Field Rule: For loads under 10mA, add a bleeder resistor in parallel. For a 24VDC signal, use a 2.4kΩ resistor (10mA bleed current, 0.24W dissipation—use a 0.5W resistor). This ensures minimum contact wetting current and reliable switching.

No Hold Last State OptionUnlike the MDL916, the MDL930 has no configurable Hold Last State. When the CPU stops or loses communication with the module, all relays de-energize immediately. If your application requires outputs to maintain their last state during CPU faults, you need MDL916 (with DIP switch Hold Last State option) or an external latching relay scheme.

• Field Rule: For critical outputs that must maintain position during CPU faults (e.g., damper positions, valve holds), use with Hold Last State enabled, or add external latching relays wired in a “maintained” configuration.

Series 90-30 Compatibility ConfusionThe IC694MDL930 can be installed in both RX3i and Series 90-30 backplanes. The IC693MDL930 is the Series 90-30 specific version. Both are functionally identical, but the part number determines which documentation and spare parts inventory to use.

• Field Rule: When replacing modules in a Series 90-30 rack, you can use either IC694MDL930 or IC693MDL930—they’re interchangeable. For RX3i racks, use IC694MDL930. Update your spare parts list to standardize on IC694MDL930 for both platforms.

Commercial Availability & Pricing Note

Please note: The listed price is for reference only and is not binding. Final pricing and terms are subject to negotiation based on current market conditions and availability.