Overview
The Douglas Randall R40D is a solid-state relay proportional controller built for industrial-grade power distribution and switching applications. With a 480VAC input rating and 40A output capacity, the R40D provides reliable control of AC loads in manufacturing, HVAC, process control, and other heavy-duty industrial environments. This model is no longer manufactured by Kidde/Douglas Randall, making it increasingly difficult to source as replacements become necessary.
Key Features
- Solid-state relay construction—no moving contacts means extended reliability and faster switching
- 480VAC nominal coil voltage for compatibility with standard industrial power systems
- 40A rated output current suitable for moderate to high-power load control
- Proportional control capability enables precise regulation of AC power to connected equipment
- Compact industrial form factor for panel mounting in control cabinets
Technical Specifications
- Coil/Input Voltage: 480VAC nominal
- Output Current Rating: 40A maximum
- Relay Type: Solid-state relay (SSR)
- Output Type: AC switching
- Proportional Control: Yes—variable power modulation
- Manufacturer: Douglas Randall (Kidde)
- Model: R40D
- Status: Discontinued
Typical Applications
- Industrial heater and oven power regulation
- Three-phase motor soft-start control
- HVAC furnace and boiler load management
- Proportional process control in manufacturing environments
- Industrial process temperature and power regulation systems
Compatibility & Replacements
Compatible With
- Standard 480VAC three-phase industrial power systems
- Control circuits operating at 480V nominal
- Legacy industrial control panels and switchgear
- Proportional controller input signals (0–10VDC or similar, verify with your application)
Replaces / Drop-In Replacement For
- Verify compatibility with your system integrator before ordering. Douglas Randall has limited interchangeability documentation available; model numbers such as R40A and R40B may share similar mounting, but electrical specifications may differ.
Works With
- Industrial control relay logic and PLC interfaces
- Standard 480VAC distribution systems
- Legacy proportional control systems from the 1980s–2000s era
- Panel-mount cabinet infrastructure with DIN-rail or screw-terminal connections
