Understanding Normally Open Relays
Relays are electrical switches that rely on electromagnetic mechanisms to convert small electrical inputs into larger outputs. The input of electrical current activates the electromagnets, forcing them to open or close the existing electrical circuit with regard to their rest state. This action may then produce a single output signal or multiple output signals, affecting one or several circuits—and, consequently, one or several connected loads—depending on their configuration. These devices are critical to the operation of numerous electrical and electronic equipment and systems, ranging from consumer appliances to industrial and commercial units. As such, they are available in a wide range of designs and configurations to accommodate the unique requirements and restrictions of the various applications. One of the most common ways relays can be classified is by their default position—i.e., whether they are normally open or normally closed. The following article provides an overview of normally open relays, outlining what they are and their typical use cases.
What Are Normally Open Relays?
Normally open relays are designed to be in the open position by default, which means the circuit is incomplete and the connected load(s) does/do not receive any power when there is no electrical input. Operations involving these open relays typically proceed as follows:
- Power is introduced into the relay
- The power activates the relay’s electromagnet
- The electromagnet produces a magnetic field
- The magnetic field pulls the initial circuit into contact with the larger circuit
- Current flows into the larger circuit and, consequently, the connected load
- The connected load turns on
Once the flow of power into the initial circuit stops, the electromagnetic deactivates, the magnetic field dissipates, the circuit reopens, and the connected load turns off.
Applications of Normally Open Relays
As indicated above, relays are found in a wide range of electrical and electronic devices. Typical applications for normally open relays include:
- Blower motors: They can be used to delay the operation of a blower motor for a set period after the activation of the heater unit to ensure the air is adequately heated before it is circulated.
- Motors and compressors: They can stagger the startup of multiple motors or compressors activated by a single switch to prevent surges within the powerline.
- Burglar/intrusion alarms: They can delay the activation of alarms to provide authorized persons with ample time to deactivate the alarm.
- Open door warning alarms. They can activate an alert if a door (e.g., a refrigerator door) is left open beyond a set amount of time.
- Power supply sequencing: They can control the startup of one or more power supplies once the main power switch is activated.
- Oven ignitor controls: They can serve as a fail-safe mechanism for the electrical ignitors of gas-fired ovens.
- Fan controls: They can control the startup of cooling fans to prevent excessive cooling.
- Two-speed motor controls: They can facilitate the soft startup of two-speed motors.
Contact Amperite For High-Quality Normally Open Relays Today
As outlined above, normally open relays serve as an essential time-delay mechanism in many devices and systems. If you’re looking for high-quality time delay relays (in normally open and normally closed variations), Amperite is the ideal partner.
At Amperite Co. (a division of Olympic Controls Corp.), we manufacture time delay relays and other electrical devices for electronic distributors and original equipment manufacturers (OEMs). In addition to our standard product offerings, we offer customization capabilities for customers with highly specialized needs. For additional information about our relays and other product offerings, contact us today.