How a Relay is Wired - Oleosymusica.blog

Relays are essential components in electrical and electronic circuits, providing control and switching capabilities for various applications. In this article, we will explore the wiring process of a relay, including its types, circuit symbols, contact configurations, coil connections, and load handling capabilities.

Relay Types

Relays come in different types, such as SPST (Single Pole Single Throw), SPDT (Single Pole Double Throw), DPST (Double Pole Single Throw), and DPDT (Double Pole Double Throw). These types determine the number of poles (terminal pairs) and throws (stable positions) the relay has, allowing for different control and switching options.

Circuit Symbols

Relays are represented by specific circuit symbols. In SPDT and DPDT relays, the common terminal is denoted by “C.” This terminal serves as a shared connection point for the normally open (NO) and normally closed (NC) contacts.

Normally Open (NO) Contacts

NO contacts connect the circuit when the relay is activated and disconnect it when the relay is inactive. They are also known as Form A contacts or “make” contacts. These contacts are commonly used for applications where the circuit needs to be closed when the relay is energized.

Normally Closed (NC) Contacts

NC contacts disconnect the circuit when the relay is activated and connect it when the relay is inactive. They are also known as Form B contacts or “break” contacts. These contacts are useful when the circuit needs to be closed by default and open when the relay is energized.

Change-Over (CO) or Double-Throw (DT) Contacts

CO or DT contacts control two circuits, with one normally open contact and one normally closed contact sharing a common terminal (C). These contacts are also called Form C contacts or “transfer” contacts. They provide the ability to switch between two different circuits based on the relay’s activation.

Coil Connection

When wiring a relay, identifying the terminals that connect the coil is crucial. The coil is typically marked by small strands of wire connected to the bottom two terminals of the relay. Applying the appropriate voltage to the coil activates the relay, causing the contacts to change their state.

Switch/Contact Terminals

The remaining terminals on the relay are switch/contact terminals. The relay usually has a diagram embossed on the top, providing a reference for the wiring connections. This diagram illustrates the positions of the contacts when no power is applied to the coil, known as the de-energized state.

Normally Open and Normally Closed States

In the de-energized state, the embossed diagram on the relay indicates which points are normally open and normally closed. The normally open contacts will be closed (conducting) when the coil is energized, while the normally closed contacts will open (interrupting) the circuit in the presence of coil activation.

Coil Voltage and Load Handling

The data tag on a relay provides valuable information about the coil voltage and the load handling capabilities of the contacts. It specifies the maximum load, such as locked rotor amps (LRA) and full load amps (FLA), that the contacts can handle at different voltages for inductive (magnetic) loads like motors, as well as resistive loads like heaters or incandescent lights.

Sources:

“All You Need to Know About Relays” – Instructables (https://www.instructables.com/All-You-Need-to-Know-About-Relays/)
“How to Wire a Relay: 5 Easy Steps” – WikiHow (https://www.wikihow.com/Wire-a-Relay)
“Understanding Relays With the 90-340” – HVAC School (https://hvacrschool.com/understanding-relays-90-340/)

FAQs

What is a relay and how does it work?

A relay is an electrically operated switch that uses an electromagnet to control the opening and closing of its contacts. When a current flows through the coil of the relay, it generates a magnetic field that attracts a movable armature, causing the contacts to change their state.

What are the common types of relays used in wiring applications?

Common types of relays used in wiring applications include SPST (Single Pole Single Throw), SPDT (Single Pole Double Throw), DPST (Double Pole Single Throw), and DPDT (Double Pole Double Throw) relays. These types offer different configurations for controlling and switching electrical circuits.

How are the coil connections of a relay identified?

The coil connections of a relay can be identified by locating the bottom two terminals of the relay. These terminals are typically marked with small strands of wire connected to them. Applying the appropriate voltage to these coil terminals activates the relay.

What are the different types of contact configurations in a relay?

Relays have different contact configurations, including normally open (NO) contacts, normally closed (NC) contacts, and change-over (CO) or double-throw (DT) contacts. NO contacts close the circuit when the relay is activated, NC contacts open the circuit when the relay is activated, and CO or DT contacts provide both a normally open and a normally closed contact.

How can I determine the de-energized state of a relay?

The de-energized state of a relay refers to the state of its contacts when no power is applied to the coil. The de-energized state can usually be determined by referring to the embossed diagram on the top of the relay, which indicates which points are normally open and normally closed in this state.

What is the purpose of the common terminal in a relay?

The common terminal, often denoted as “C,” is a shared connection point for the normally open (NO) and normally closed (NC) contacts in SPDT and DPDT relays. It serves as a reference point for switching between the two contact positions based on the relay’s activation.

How do I connect a relay to an electrical circuit?

To connect a relay to an electrical circuit, you need to identify the coil terminals and the switch/contact terminals. Connect the appropriate voltage source to the coil terminals to activate the relay, and then wire the desired electrical load to the switch/contact terminals according to the specific requirements of your application.

What should I consider when selecting a relay for a wiring application?

When selecting a relay for a wiring application, consider factors such as the coil voltage requirement, the type and number of contacts needed, the maximum load capacity of the contacts, and any specific environmental or operational conditions that may affect the relay’s performance.