Aprilaire 8024 24V Universal SPDT Isolation Relay Card

Aprilaire 8024 Three-Relay 24V Dry Contact Switching Card

The Aprilaire 8024 is a 24-volt relay card designed for general-purpose use in HVAC and environmental control applications. It contains three SPDT (Single-Pole, Double-Throw) relays that can each be switched independently. The coils on all three relays share a common circuit. The 8024 functions as a dry contact switching device, making it suitable for interfacing dehumidifiers and other environmental control equipment with grow room automation systems.

In grow room applications, the 8024 is commonly used as an isolation relay to allow a low-voltage control signal from an environmental controller to switch higher-voltage loads — such as dehumidifiers, humidifiers, or CO2 injection equipment — without direct electrical connection between the control system and the load circuit. The three independent SPDT relays allow multiple control channels to be managed through a single relay card.

Key Features & Benefits

• Three Independent SPDT Relays — Three independently switched Single-Pole, Double-Throw relays for versatile control.
• 24-Volt Operation — Operates at 24V for compatibility with standard HVAC and environmental control systems.
• Shared Coil — Coils share a common circuit, simplifying wiring in multi-relay applications.
• Dry Contact Switching — Provides isolated dry contacts for interfacing between control systems and equipment.
• General Purpose — Suitable for a wide range of environmental control and automation applications.
• Isolation Function — Electrically isolates the control circuit from the load circuit for safety and compatibility.

Who Should Use This Relay Card

The Aprilaire 8024 is suited for grow room operators integrating Anden or other dehumidifiers, humidifiers, or environmental equipment with automation controllers that require isolated dry contact outputs. It is also used in building automation, HVAC, and other environmental control applications where isolation relays are needed.

SPDT Relay Basics – Normally Open and Normally Closed Contacts

An SPDT (Single-Pole, Double-Throw) relay has three contact terminals: Common (COM), Normally Open (NO), and Normally Closed (NC). When the relay coil is not energized, current flows between COM and NC — the normally closed position. When the coil is energized, the relay switches and current flows between COM and NO — the normally open position. This allows a single relay to both make and break circuits with one control signal. In environmental control applications, SPDT relays are used to activate equipment when a controller signals demand (energizing the coil) and de-activate it when the demand is satisfied.

Frequently Asked Questions

How many relays does the 8024 have?

The Aprilaire 8024 contains three SPDT relays that can be switched independently.

What voltage does it operate at?

The 8024 operates at 24 volts AC/DC.

What does SPDT mean?

SPDT stands for Single-Pole, Double-Throw. Each relay has a common contact that can connect to either a normally open or normally closed contact, allowing it to make and break circuits.

What is a dry contact relay?

A dry contact relay provides switching contacts that are not connected to any voltage source. The contacts carry the external circuit's voltage, not the relay's own power supply. This allows electrical isolation between the control circuit and the controlled load.

Can each relay be switched independently?

Yes. All three SPDT relays on the 8024 can be switched independently, even though the coils share a common circuit.