MTL7729P+ | Eaton MTL Single Channel NAMUR Input Zener Intrinsic Safety Barrier Ex ia DIN Rail

The MTL7729P+ is a high-performance 2-channel shunt-diode safety barrier (Zener barrier) from Eaton's Crouse-Hinds series MTL7700 range, specifically engineered for intrinsic safety applications in IIB gas groups requiring easy maintenance and module replacement without rewiring.

This passive device limits the voltage and current that can reach a hazardous area under fault conditions, preventing ignition of flammable atmospheres. With a safety description of 28V, 164 Ω, 170mA, the MTL7729P+ is the ideal solution for protecting 2-wire transmitters, switch inputs, solenoid valves, and other low-power devices in Zone 0, 1, and 2 hazardous locations (IIB gas group).

• Pluggable Design - UNIQUE: Modules plug into a dedicated backplane/carrier - can be easily replaced without disturbing field wiring, significantly reducing downtime and maintenance costs
• 2-Channel Efficiency: Two independent intrinsically safe channels in a single pluggable module - protects two field devices while maximizing cabinet space efficiency
• IIB Gas Group Certification: Specifically designed for IIB gas groups (e.g., ethylene) - certified for use in Zone 0, 1, and 2 hazardous locations
• 28V Safety Description: Provides safe voltage limiting for analog and digital circuits with Uo = 28V, Io = 170mA, Po = 1.19W
• 164 Ω End-to-End Resistance: Matches typical loop resistance requirements for 4-20 mA signal circuits while ensuring intrinsic safety compliance
• 170mA Maximum Current: Higher current capability suitable for solenoid valves, I/P converters, and other low-power field devices
• Low Voltage Drop (3.68V @20mA): Ideal for I/P converter applications with power-limited field devices
• Bussed Power Capability: Integrated bussed power distribution reduces cabling requirements
• Dual-Stage Protection: Two stages of pulse-tested Zener diodes ensure continued safety if either stage should fail
• Global Approvals: CCC Ex (China valid until 2030-09-01), TIIS (Japan - expired 2024-11-03), ATEX, and IECEx certifications

The MTL7729P+ is a passive shunt-diode safety barrier that operates on the Zener barrier principle. It limits both voltage and current that can be delivered to a hazardous area circuit under fault conditions.

• Voltage limiting: Zener diodes clamp the output voltage to a safe level (28V) if the safe-area voltage rises above normal operating levels
• Current limiting: A series resistor (164Ω) limits fault current to a safe value (170mA)
• Fusing: Internal fuses provide backup protection under severe fault conditions
• Two-stage voltage limitation: Two stages of pulse-tested Zener diodes ensure continued safety if either stage should fail
• Grounding: The barrier requires a connection to a high-integrity earth ground via the backplane system

The MTL7729P+ is specifically designed for IIB gas group applications requiring easy module replacement:

• 2-wire 4-20 mA transmitters (pressure, temperature, level, flow)
• I/P converters for valve positioning
• Solenoid valves
• Switch inputs (limit switches, pressure switches)
• Low-power analog output circuits

• A high-integrity earth ground connection is mandatory for proper Zener barrier operation
• The barrier must be installed in a safe area (non-hazardous location)
• NOT certified for IIC gas groups (hydrogen, acetylene) - for IIB only
• Requires compatible MTL7700 series backplane/carrier (sold separately)
• Maximum cable parameters for IIB gas group: Co = 1.41 μF, Lo = 240 mH