Tyco Hartman A-703B Aircraft Power Relay

TYCO ELECTRONICS HARTMAN A-703B AIRCRAFT POWER RELAY SPST-NO 400A 28VDC

The Tyco Electronics / Hartman A-703B is a military-grade single-pole single-throw normally open (SPST-NO, Form X) high-current DC power contactor engineered specifically for demanding aerospace, naval marine, and severe-duty mobile defense systems. Built under Hartman’s high-reliability power switching portfolio (now TE Connectivity), the A-703B provides continuous current carrying capability up to 400 Amperes at 28 VDC nominal, engineered to handle extreme inrush currents, inductive load switching, and severe mechanical vibration.

The unit features heavy-duty silver-alloy main power contacts arranged in a double-break configuration to rapidly quench DC arc formation. Housed within a ruggedized, corrosion-resistant, environmentally sealed enclosure, the A-703B prevents moisture intrusion, galvanic oxidation, and contact fouling common in marine saltwater atmospheres and unpressurized avionics bays.

Model Details

• Manufacturer: Hartman Electrical Mfg. Co. / TE Connectivity (Tyco Electronics)
• Part Number / MPN: A-703B
• Series: Hartman A-700 / K-Series Heavy Duty High-Amperage DC Contactor Family
• Internal / Sub-Assembly Identifiers: A703B, AH-703B, K400-Series variant

Technical Specifications

Key Features

1. 400A Continuous High-Capacity Switching: Handles sustained 400 Ampere resistive/inductive bus loads at 28 VDC with an overload interrupt rupture capacity exceeding 3,200A.
2. Double-Break SPST-NO Contact Architecture: Form X contact geometry provides dual air gaps upon de-energization, splitting the arc voltage for rapid arc extinction and extended contact service life.
3. Continuous-Duty 28VDC Actuation Coil: Low-draw, continuous-duty magnetic coil engineered to stay locked in harsh high-vibration profiles without overheating.
4. Hermetic / Gasket Environmental Sealing: Rugged metal housing engineered to meet harsh aero-marine ingress barriers, suppressing electrolytic salt-air corrosion, fuel mist, and hydraulic vapors.
5. Dedicated High-Torque Stud Terminals: Heavy copper-alloy threaded power terminal studs ensure minimal millivolt drop across connections under sustained 400A marine and aviation switchboard loads.

Compatibility

• Aviation Airframes & Power Carts: Turboprop and business jet primary 28VDC bus tie circuits, starter-generator disconnect systems, Auxiliary Power Unit (APU) start circuits, and ground power units (Hobart, Tronair, Tug 28V GPU assemblies).
• Naval & Marine Systems: Fast patrol vessels, commercial workboats, offshore support vessels (OSVs), battery bank isolation switches, bow thruster 24V/28V DC disconnect circuits, and fire pump backup DC starter contactors.
• Heavy Armored & Industrial Mobile Units: Military tracked/wheeled combat platforms, remote generator transfer switches, high-amperage hydraulic power pack prime contactors, and mine-haul auxiliary battery banks.

Part Number Cross-References

• TE Connectivity / Hartman: A-703B, A703B, A-703A, A-703C, AH-703B
• Military / Standard Equivalents: Cross-checks against MIL-R-6106 heavy-duty 400A series and MS27433 type contactor envelopes.
• Direct Application Replacements: Hartman K400A-series 28VDC 400A busbar-mount or stud-mount platforms.

Applications

• Starter-Generator Main Disconnect: Switching high inrush generator outputs into the central DC tie-bus without contact welding.
• Marine Emergency Battery Isolation: Safe galvanic disconnection of high-capacity lithium iron phosphate (LiFePO4) or lead-acid marine starting banks.
• APU DC Start Relays: Providing sustained cranking currents for auxiliary power engines on aircraft and commercial vessels.
• Aviation Ground Power Feeds: Serving as the internal protective line contactor inside 28.5 VDC flightline ground support units.
• Direct Current Capstan & Winch Isolation: Isolating marine mooring winches and crane hydraulic prime power feeds.

Frequently Asked Questions

What is the maximum continuous current capacity of the Hartman A-703B?

The Hartman A-703B is rated for 400 Amperes continuous direct current (DC) at a nominal working voltage of 28 VDC in standard ambient configurations.

What is the contact form of the Hartman A-703B relay?

It utilizes an SPST-NO (Single Pole, Single Throw, Normally Open) configuration with double-break (Form X) contacts. This design splits the arc gap across two points, providing superior arc suppression compared to single-break units.

Can the A-703B operate on 24VDC marine or industrial vehicle battery systems?

Yes. Although rated nominally for 28 VDC (standard aviation bus voltage), the coil pick-up voltage is engineered at a maximum of 18 VDC, allowing reliable latching on standard 24VDC battery systems even under engine-crank voltage-drop conditions.

How do I troubleshoot an A-703B contactor that will not close?

Measure the voltage across the coil control terminals while energizing. If the voltage is at or above 18 VDC and the unit does not pull in, de-energize and check coil resistance with a multimeter. An open circuit or near-zero resistance indicates coil failure. If the coil pulls in with an audible mechanical click but power is not transferred across the load terminals, verify main bus continuity and check for severe internal contact erosion.

What causes terminal overheating on high-amperage relays like the A-703B?

Terminal overheating is almost universally caused by insufficient terminal nut torque, improper hardware stacking (such as placing a steel washer between the cable lug and the bus pad), undersized conductor cross-sections for 400A loads, or severe oxidation on terminal mating surfaces.