MTL7778AC Dual Channel Zener Barrier with 28 V Working Voltage and DIN Rail Mount for Hazardous Areas

The MTL7778AC is a high-performance 2-channel shunt-diode safety barrier (Zener barrier) from Eaton's Crouse-Hinds series MTL7700 range, specifically engineered for AC and DC systems 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 working voltage of 28 V, end-to-end resistance of 600 Ω, and maximum current of 47 mA, the MTL7778AC is the ideal solution for protecting AC/DC sensors, thermocouples, and other low-level analog input devices in Zone 0, 1, and 2 hazardous locations (gas groups IIC, IIB, IIA).

The device features a compact 12 mm width and standard DIN rail mounting for easy integration into existing control cabinets. The "AC" suffix indicates a non-polarized, star-connected barrier configuration.

The "AC" suffix indicates a non-polarized, star-connected barrier configuration suitable for both AC and DC circuits, distinguishing it from polarity-sensitive models (MTL7778+ or MTL7778-).

• 2-Channel Efficiency: Two independent intrinsically safe channels in a single compact housing — protects two field devices while using minimal panel space
• AC/DC Compatibility: The non-polarized, star-connected configuration allows Vwkg to be developed from each channel to ground, providing common-mode voltage capability and allowing higher cable parameters to be used
• 28 V Working Voltage: Provides safe voltage limiting for AC/DC circuits, preventing ignition under fault conditions
• 600 Ω End-to-End Resistance: Matches the impedance requirements for AC/DC sensor and thermocouple applications
• 47 mA Maximum Current: Adequate current handling for low-level analog input devices
• 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: Reduces cabling requirements with integrated bussed power distribution — a unique feature of the MTL7700 series
• Angled Wire Entry: Wire entry is angled to assist wiring within limited space enclosures
• Ultra-Slim DIN Rail Mounting: Compact 12 mm width for standard 35 mm DIN rail installation — simultaneously makes a reliable IS earth connection when clipped onto the rail
• Dual-Stage Protection: Two stages of pulse-tested Zener diodes and an 'infallible' terminating resistor ensure continued safety if either stage should fail
• Proven MTL7700 Series Heritage: Following closely in the footsteps of the MTL700 range (established as the worldwide standard for safety barriers since 1984), the MTL7700 range provides quick and easy DIN rail installation
• Global Approvals: CCC Ex (China valid until 2030-09-01) and ATEX/IECEx certifications for international installation flexibility

The MTL7778AC 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 (28 V) if the safe-area voltage rises above normal operating levels
• Current limiting: A series resistor (600 Ω) limits fault current to a safe value (47 mA)
• Fusing: Internal 50 mA fuses provide backup protection under severe fault conditions
• Star-connected configuration: The "AC" designation indicates a non-polarized, star-connected barrier configuration where Vwkg can be developed from each channel to ground, providing common-mode voltage capability
• Grounding: The barrier requires a connection to a high-integrity earth ground — made simultaneously when clipping onto standard T-section DIN rail

The MTL7778AC is specifically designed for AC and DC system protection in hazardous area installations:

• AC/DC powered sensors
• Thermocouples
• Low-level analog input devices
• AC proximity detectors
• General-purpose AC/DC circuits in hazardous areas

• Optimized for AC/DC Systems — Unlike single-polarity barriers, the MTL7778AC features a star-connected, non-polarized configuration specifically designed for AC and DC systems, providing common-mode voltage capability and allowing higher cable parameters.
• 2-Channel Efficiency — With two independent channels in a single compact 12 mm housing, the MTL7778AC protects two field devices while using minimal panel space.
• Unique Removable Terminals — Unlike competitors, the MTL7778AC features removable terminal blocks that simplify cabling, maintenance, and barrier replacement without rewiring. The terminals can be unplugged from the side of the module for loop disconnect.
• Bussed Power Capability — Integrated bussed power distribution reduces cabling requirements and installation costs — a unique feature of the MTL7700 series.
• Angled Wire Entry — Wire entry is angled to assist wiring within limited space enclosures, making installation easier in crowded control cabinets.
• Proven MTL Heritage — Since its introduction in 1984, the MTL700 range established itself as the worldwide standard for safety barriers. The MTL7700 range follows closely in its footsteps, providing quick and easy DIN rail installation.
• Global Approvals — Certified for use in major industrial markets including CCC Ex (China valid to 2030), ATEX (Europe), and IECEx (international), the MTL7778AC simplifies global equipment standardization.
• Simple Installation — DIN rail mounting with simultaneous IS earth connection, clearly labeled terminals, removable terminal blocks, and compact 12 mm width make installation quick and intuitive.

• 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)
• Maximum cable parameters for IIC gas group: Co = 0.083 μF, Lo = 3.05 mH
• Maximum cable parameters for IIB gas group: Co = 1.41 μF, Lo = 240 mH
• The star-connected configuration provides common-mode voltage capability

The MTL7700 series offers a complete range of shunt-diode safety barriers for all intrinsic safety applications.