MTL7728P+ Eaton MTL 4-20mA Zener Safety Barrier

The MTL7728P+ is a high-performance 1-channel shunt-diode safety barrier (Zener barrier) from Eaton's Crouse-Hinds series MTL7700 range, specifically engineered for high-power applications in IIC gas groups (hydrogen, acetylene, etc.) requiring intrinsic safety protection in hazardous areas.

This passive device limits the voltage and current that can reach a hazardous area under fault conditions, preventing ignition of flammable atmospheres. With a maximum output voltage of 28V DC, switching current of 119mA, and a low voltage drop of only 5.1V at 20mA, the MTL7728P+ is the ideal solution for protecting solenoid valves, alarms, LEDs, and controller outputs in Zone 0, 1, and 2 hazardous locations (gas group IIC).

The "P" designation indicates the higher-power version with lower voltage drop (5.1V vs 6.66V), distinguishing it from the standard MTL7728+. The "+" indicates positive polarity.

• High-Power IIC Certification: Certified for the most hazardous IIC gas groups (hydrogen, acetylene) – suitable for use in Zone 0, 1, and 2 explosive atmospheres
• Low Voltage Drop – UNIQUE: Only 5.1V voltage drop at 20mA – significantly lower than the standard MTL7728+ (6.66V), maximizing available power for field devices in power-limited applications
• 1-Channel with Higher Current: Single channel rated for 119mA switching current – higher capacity than standard IIC barriers (typically 93mA)
• Ideal for Solenoid Valves & Alarms: Specifically recommended for digital (switch) outputs including solenoid valves, alarms, LEDs, and controller outputs
• Controller Output Optimization: Recommended choice for controller outputs where power budget is critical – provides more headroom for I/P converters and other analog outputs
• Removable Terminals: Unique removable terminal blocks for easy cabling, maintenance, and loop disconnect by simply unplugging terminals from the side of the module
• Bussed Power Capability: Integrated bussed power distribution reduces cabling requirements. When used with the MTL7798 power feed module, provides a fully protected, electronically fused supply with no additional wiring required
• Angled Wire Entry: Wire entry is angled to assist wiring within limited space enclosures, making installation easier in crowded control cabinets
• Ultra-Slim DIN Rail Mounting: Compact 12.6 mm width for standard 35 mm T-section DIN rail – simultaneously makes a reliable IS earth connection when clipped onto the rail
• Dual-Stage Protection: Contains two stages of pulse-tested Zener diodes and an 'infallible' terminating resistor. The two stages of voltage limitation ensure continued safety if either stage should fail
• Global Approvals: ATEX, IECEx, UL, CSA certifications for international installation flexibility

The MTL7728P+ 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 limits fault current to a safe value (119mA)
• 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 – made simultaneously when clipping onto standard T-section DIN rail

The MTL7728P+ is specifically designed for high-power digital and analog output applications in IIC hazardous area installations:

• Solenoid valves (low-power)
• Audible and visual alarms
• LED indicators
• I/P converters (current-to-pressure) for valve positioning
• Controller analog outputs (0/4-20 mA)
• Digital (switch) outputs

• A high-integrity earth ground connection is mandatory for proper Zener barrier operation
• Do not install in areas where condensation may occur
• The barrier must be installed in a safe area (non-hazardous location)
• Hazardous-area terminals are identified by blue labels
• For bussed power applications, use with MTL7798 power feed module
• Compatible with existing MTL700 range installations – direct replacement