Hidden Feature of DCT24ENC and DCT24PB – Control 240 V Loads with an External Relay

Safely switch mains-powered devices using the DCT24 Digital Countdown Timer

The DCT24ENC and DCT24PB are one of Bolec Electronics’ most versatile digital countdown timers for 12V and 24V systems.
At first glance it appears to be a low-voltage-only device — but with a simple addition of an external relay,
it can also safely control 240VAC equipment.

Why Use an External Relay?

The internal relay inside the DCT24 provides volt-free contacts rated at 1A / 30VDC (resistive).
This rating is perfect for low-voltage signal or control circuits — but not sufficient for switching high-voltage or
high-current loads such as pumps, heaters, or lighting.

By connecting an external relay coil to the DCT24 output, you can use the timer to drive a higher-rated
relay or contactor that switches the 240V circuit safely and reliably.

Basic Wiring Concept

When wired for 240 V applications, the DCT24’s volt-free output (COM–NO) energizes the coil of an external relay.
The external relay then switches the 240 V line to the connected load such as lights, motors, or heaters.

• COM–NO of DCT24 → coil of external relay
• External relay contacts → 240V line to load
• LED A indicates relay energized; LED B flashes while countdown is active

⚠️ 240 V wiring must be carried out by a licensed electrician.

Practical Applications

• Run a 240V fan or light for a preset duration
• Time-limited heater or compressor control
• Industrial equipment or irrigation pump shutdown timer

Quick Setup

1. Press the rotary dial to wake up the timer
2. Turn to set hours → press → turn to set minutes → press
3. Hold dial for 1 second to start countdown
4. During countdown: COM–NO contacts closed (relay active)
5. When countdown ends: timer resets to the last set time

Safety and Reliability

The DCT24 itself never switches the mains voltage directly.
Using an external relay ensures that the timer remains isolated from the high-voltage circuit — allowing you to
enjoy the convenience of digital timing with the safety required for 240V systems.

If you need help selecting a suitable external relay or wiring configuration, feel free to contact our team.