Normally Open Vs Normally Closed Relay, Diagrams, Symbols

Normally Open Vs Normally Closed Relay

A relay is an electrically operated switch that can be used to control a circuit using a low-power signal. Relays are often used in automotive applications where it is necessary to control a circuit using a low-power signal from a switch or sensor.

A relay has different types of configurations. The normally open relay and the normally closed relay are a state of the relay. It is the open and closed position of contacts in the relay. A car uses different types of relays depending on the need of the work, so it is important to know the concept of the normally open and normally closed relay.

In this powerful guide, you will learn the normally open relay and normally closed relay, diagrams, symbols, and how to check them.

Related Post: Car Relay Guide

First Understand The Wiring Diagram Of Relay

4 Pin Relay Wiring Diagram
4 Pin Relay Wiring Diagram

Before wiring the relay first, you should understand the wiring diagram of the relay. A relay has two circuits, a coil, and high amperage circuit. Each circuit has two terminals. The coil circuit’s terminals are 85 and 86. Terminal 85 is given a negative power source, and 86 is given a positive power source.

The relay’s second high amperage circuit consists of two terminals called 30 and 87, in which terminal 30 is a common terminal. It means through terminal 30, the battery’s 12-volt power source enters the relay. Similarly, the relay’s high amperage circuit’s terminal 87 is considered a power-out terminal. It means through terminal 87, the 12-volt power leaves the relay and goes to the component.

5-Pin-Relay-Wiring-Diagram
5-Pin-Relay-Wiring-Diagram

In a five-pin relay, the relay’s high amperage circuit consists of three terminals, 30, 87, and 87a. Terminal 87a is a fifth extra terminal used for circuits when power is required without energizing the relay.

Related Post: Automotive Relay Diagram

Normally Open Relay

The normally open (NO) relay means, by default, the relay’s contacts are open and do not have connections. When the relay’s high amperage circuit contacts (Terminal 30 and 87) stay separate from each other without energizing the relay in normal conditions. This type of relay is called the Normally Open (NO) relay.

If you connect a normally open relay in a circuit, it will not let the current pass. By energizing the relay, the relay’s contacts close, and the current starts to flow. Normally open relays are used everywhere in the car, such as air conditioners, fog lights, horns, fans, etc.

Normally Open Relay Symbol

Normally Open Relay Symbol
Normally Open Relay Symbol

This is the symbol of the normally open relay. It is used for representing the contacts of the relay that are open when there is no power supplied. It means the contact is open (break) & there is no flow of current by default and gets closed and starts the current flow when activated.

This is an Info
The open and closed position of a relay depends upon the design and need for work in a car.

This is an Info
By default, some four-pin relays are Normally Open (NO), and some are Normally Closed (NC).

Normally Open Relay Diagram

Normally Open Relay Diagram
Normally Open Relay Diagram

In the above picture, you can see a normally open relay diagram, in which the relay’s high amperage circuit’s contacts are open and do not have a connection. By energizing the relay, the relay’s high amperage circuit’s contacts will change from an open to a closed state and create a path for the current to flow.

How To Check Normally Open (NO) Relay Contacts

  • Identify the relay’s high amperage circuit.
  • Take the multimeter and put it in ohm or continuity mode.
  • Touch the multimeter ohm or continuity leads with the relay’s high amperage circuit
  • If you get some reading in ohmmeter, it means your contacts are bad. If you get an Open Load (OL) reading in the ohmmeter, it means your normally open contacts are in good condition.
  • If you do not get a beep sound in continuity mode, it means the contacts are good, but if get a beep sound it means the contacts are bad.

Related Post: How To Wire A 4 Pin Relay For Horn & Lights

Normally Closed Relay

The normally closed relay is the opposite of the normally open relay in function. When the relay’s high amperage circuit’s contacts (Terminal 30 and 87) are closed (Touch) each other without energizing the relay in normal conditions, called Normally Closed (NC). The normally closed relay’s contacts are closed by default and have a connection. It will remain in the closed position until the relay is energized.

Normally Closed Relay Symbol

Normally Closed Relay Symbol
Normally Closed Relay Symbol

This is the symbol of the normally closed relay. The normally closed relay’s contacts are in the closed position when there is no power supplied. The relay’s contacts open when the relay activates to break the circuit.

Normally Closed Relay Diagram

Normally Closed Relay Diagram
Normally Closed Relay Diagram

In the above, normally closed relay diagram, the relay’s high amperage circuit contacts are by default closed, and the current is flowing even if the relay is not energized. These contacts will open when the relay is energized, and the current will stop flowing.

Related Post: SPST Relay Vs SPDT Relay

How To Check Normally Closed (NC) Relay Contacts

Normally Closed Relay
Normally Closed Relay
  • Identify the relay’s high amperage circuit.
  • Take the multimeter and put it in ohm or continuity mode.
  • Touch the multimeter ohm or continuity leads with the relay’s high amperage circuit.
  • If you get some reading in ohmmeter, it means your contacts are ok. If you get an Open Load (OL) reading in ohmmeter, it means your normally open contacts are bad.
  • If you do not get a beep sound in continuity mode, it means the contacts are bad, but if get a beep sound it means the contacts are good
Five-Pin-Relays-Normally-Open-and-Closed-Terminals
Five-Pin-Relays-Normally-Open-and-Closed-Terminals

Note:

Five-pin relays have the contact points at the same time, Normally Open (NO) and Normally Closed (NC). This extra 87a terminal gives the five-pin relay both features at the same time.

As you can see, learning normally open and closed relay is no more a mystery, anyone can learn in a few minutes.

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Frequently Asked Questions (FAQs)

What is the difference between a normally open and normally closed relay?

Normally open relay is a type of relay in which the contacts are open in the normal or relaxed state. Normally closed relay is a type of relay in which the contacts are closed in the normal or relaxed state. The main difference between a normally open and normally closed relay is that, in a normally open relay, the circuit is open when the relay is in its relaxed state (is not yet energized) whereas, in a normally closed relay, the circuit is closed when the relay is in its relaxed state or is not yet energized.

Which part of the relay causes the most trouble?

The part of the relay that causes the most trouble is typically the contact point. This is because, over time, the contact point can become corroded or damaged, which can cause problems with the electrical current flowing through the relay. In some cases, simply cleaning the contact point can solve the problem. However, if the damage is more severe, it may be necessary to replace the entire relay.


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