Product Brief: Bently Nevada 3500/32M 125720-02 (4-Channel Relay Module with Intrinsic Safety Barriers)
The 3500/32M 125720-02 is a 4-channel relay module with integrated intrinsic safety (IS) barriers for the Bently Nevada 3500 series machinery protection system. This module provides alarm and trip relay outputs directly from the 3500 rack, while the -M suffix indicates internal safety barriers that allow the relay contact wiring to exit into hazardous area (Class I, Division 1 / Zone 1) environments without requiring external isolators. The 125720-02 is a specific version with form C (SPDT) relays and certified IS outputs for each channel.
It receives alarm/danger signals from monitoring modules (e.g., 3500/40, 3500/42, 3500/60) via the rack backplane and provides dry contact relay outputs to field devices such as emergency shutdown systems (ESD) , trip solenoid valves, alarm annunciators, or PLC/DCS inputs located in hazardous areas.
Key Features
4 independent relay channels – each with form C (SPDT) contacts.
Integrated intrinsic safety barriers – certified for Class I, Div 1/Zone 1/Zone 2 hazardous areas.
Direct replacement for 3500/32 with external barriers – simplifies installation and reduces cabinet space.
Programmable relay logic – latching/non-latching, normally energized/de-energized, time delays (via configuration software).
Backplane communication – receives alarm status from any 3500 series monitor module.
Redundant power supply compatible – operates with single or dual 3500/15 power supplies.
Hot-swappable – replace without rack power-down.
Parameters (Table)
| Parameter | Specification |
|---|---|
| Model | 3500/32M |
| Part Number | 125720-02 |
| Product Type | 4-channel relay module with internal IS barriers |
| Dimensions (Height x Width x Depth) | 241 mm x 25 mm x 242 mm (9.5 in x 1.0 in x 9.5 in) – occupies one slot in 3500 rack |
| Weight (approx.) | 1.0 kg (2.2 lb) |
| Number of Relay Outputs | 4 independent channels |
| Relay Type | Form C (SPDT) – Common (C), Normally Open (NO), Normally Closed (NC) |
| Contact Rating (safe area side) | 5 A @ 250 VAC / 30 VDC (resistive load) |
| Contact Rating (hazardous area side) | Limited by IS entity parameters – typically ≤ 1 A @ 30 VDC |
| IS Output Entity Parameters (per channel) | Voc ≤ 30 VDC, Isc ≤ 100 mA, Ca ≥ 0.05 µF, La ≥ 0.5 mH (depending on certification) |
| Hazardous Area Certification | Class I, Div 1 & 2 (Groups A-D); Zone 1/2 (IIB, IIC) – with appropriate application |
| Input from Backplane | Alarm/Danger status from any 3500 monitor module (e.g., 3500/40, 3500/42, 3500/60, 3500/91) |
| Relay Logic Programmability | Configurable per channel: normally energized/de-energized, latching/non-latching, time delay (0–60 seconds) |
| Response Time | < 50 ms (from alarm trigger to relay change of state) |
| Relay Life (mechanical) | 10 million operations (typical) |
| Relay Life (electrical) | 100,000 operations at rated load |
| Power Consumption | 5 W (typical from rack backplane) |
| Operating Temperature | -30°C to +65°C (-22°F to +149°F) |
| Storage Temperature | -40°C to +85°C (-40°F to +185°F) |
| LED Indicators | Per channel: OK, Alarm/Danger, Relay energized |
| Field Wiring Connection | Via external termination module (e.g., 3500/32M terminal block) – sold separately |
| Approvals (Typical) | CSA, ATEX, IECEx, EAC (depending on revision – verify with factory) |
Application Scenarios (use cases)
| Application Area | Description |
|---|---|
| Gas Turbine in Zone 1 Compressor Building | Relay module mounted in 3500 rack (safe area) provides IS barrier outputs directly to shutdown solenoid in explosive environment without external barrier. |
| Offshore Platform Emergency Shutdown (ESD) | Drives ESD valves (located in Zone 1) for high compressor vibration or overspeed – simplifies wiring and reduces junction boxes. |
| Refinery Wet Gas Compressor Trip System | Hazardous area trip outputs to vibration/overspeed solenoids – internal barriers replace bulky external barrier cabinets. |
| LNG Plant Turboexpander Shutdown | Relays located in safe area control room; field solenoids in Zone 1 area connect directly to 3500/32M outputs (IS protected). |
| Chemical Plant Compressor Train | Provides alarm annunciation to hazardous area panel (LED beacons/horns) without additional isolation. |
| Oil & Gas Wellhead Compressor | Limits wiring and installation cost by integrating barrier functions into the 3500 rack. |
| Hydrogen Compressor (IIC gas group) | Internal barriers certified for IIC (hydrogen/acetylene) – suitable for highest risk gas groups. |
| Retrofit of Old 3500/32 + External Barriers | Replaces separate relay module and external IS barrier assembly, saving cabinet space and reducing wiring errors. |
Notes
125720-02 is the relay module only – requires a separate termination module (e.g., 3500/32M termination board, part number varies by region) for field wiring connections.
-M version = Internal Intrinsic Safety Barriers. Standard 3500/32 (no -M) requires external barriers for hazardous area wiring.
Do NOT connect non-IS field devices that exceed entity parameters (voltage/current/capacitance/inductance) – this invalidates the safety certification.
Entity parameters listed are typical. Always verify the exact values on the module certificate for your specific revision (e.g., Rev B, Rev C).
Power supply – the 3500/32M is powered by the rack backplane; no external power needed for the module itself. The field loops are passive (dry contacts) – external power must be supplied in the hazardous area through IS isolators or approved power supplies.
Configuration – relay logic (latching, time delay, energize/de-energize) is set via 3500 System Configuration Software.
Channel assignment – any 3500 monitor channel (from any module in the rack) can be mapped to any relay channel via software.
First-out indication – supported for latching alarms (first channel to trip remains latched until reset).
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7×24 hours technical consultation, from selection guidance to installation and commissioning to provide full life cycle service (paid)
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