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What Are Normally Closed Relays?

Posted on by Judy Johnson

Normally Closed Relays

Time-delay relays are essential components of a variety of machines and devices. These systems convert electrical currents from different voltage levels to ensure the equipment receives the right amount of power at the right time.

Many different types of time-delay relays are in use today, including interval-on-operate, flasher, normally open, and normally closed relays. The relays are triggered by electricity, although each type of relay is triggered differently, meaning that each has its place for specific applications.

Let’s take a closer look at normally open and normally closed relays:

Normally Open vs. Normally Closed

What’s the difference between normally open and normally closed relays? Although they both are built with two circuits—one of which being larger than the other—the key difference is right in their names:

  • Normally open relay: Normally open relays default in the open position, meaning that when they’re not in use, there is no contact between the circuits. When power is introduced, an electromagnet pulls the first circuit into contact with the second, thereby closing the circuit and allowing power to flow through. When the electricity turns off, the circuit opens up again to stop the flow.
  • Normally closed relay: Normally closed relays default in the closed position, meaning that the circuit is closed unless otherwise specified. Introducing too much power draws the first circuit away from the second circuit to turn it off.

Normally open relays are more common than normally closed relays, but normally closed relays have a variety of important applications, as well.

What Are Normally Closed Relays

Normally Closed Relay Applications

Here are just a few systems that require normally closed relays.

  • Air conditioners: Normally closed relays are used to keep AC unit blowers running even after the air compressor shuts off, allowing the system to continue generating residual cool air without running the compressor.
  • Gas valve control systems: In these systems, normally closed relays act as safety features, stopping power to the gas valve in the event of a malfunction.
  • Telephone circuits: With normally closed relays, telephone calls can be terminated if no one answers within the specified amount of time.
  • Dead Man’s Seat: Certain machines are set to shut down if the driver is no longer in the seat. However, an immediate shutdown would be inconvenient if the driver merely bounces or shifts and accidentally activates that safety feature. The normally closed relay provides a time delay that takes into consideration occasional driver bounces, but it maintains that safety precaution by allowing for a shutdown if the driver is out of the seat for too long.
  • Explosive atmospheres: G-series time-delay relays are hermetically sealed, so they can be used in explosive environments without risking fires or explosions caused by sparks.

Quality Time-Delay Relays from Amperite

At Amperite Co., we manufacture and distribute a variety of relays to suit your specific needs. If you have any questions about our products or would like to request a quote, contact us today!

What Are Normally Closed Relays

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