Normally Open Vs Normally Closed Contact Relay, Diagrams, Symbols – Understand The Differences B/W 12v 4 Pin Normally Open and Normally Closed Relays

A relay is an electrically operated switch that can be used to control a circuit using a low-power signal. It lets electricity be delivered to a device over the shortest possible distance to reduce voltage loss. It is widely used in a variety of applications, including automotive, industrial, and household systems, where it is necessary to control a circuit using a low-power signal from a switch or sensor. In industrial applications, relays may be used to control motors, pumps, or other heavy-load circuits.

A relay has many types of contact 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.

Car relay information is useful for understanding how to use and maintain these electrical components in automotive systems. In this powerful guide, you will learn the normally open relay and normally closed relay, diagrams, symbols, and how to check them.

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First Understand The Wiring Diagram Of Relay

Before wiring the relay first, you should understand the wiring diagram of the relay. A relay has two circuits, a coil (electromagnet), 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.

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.

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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, like air conditioners, fog lights, horns, fans, etc.

For example, if a normally open relay is used to control a car’s headlights, the headlights would be off by default. When the relay is activated, the contacts would close and the headlights would turn on. When the relay is de-energized, the contacts would open and the headlights would turn off.

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

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 Do You Tell if a Relay is NO (Normally Open)

• 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.

For example, the headlights of a car may be controlled by a normally closed relay that is activated when the ignition switch is turned off. When the ignition switch is turned off, the relay is energized, and the contacts open, causing the headlights to turn off. This ensures that the headlights are not left on accidentally, which could drain the car’s battery.

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

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 relay contacts will open when the relay is energized, and the current will stop flowing.

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How Do You Tell if a Relay is NC (Normally Closed)

• 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

Note:

The current rating of a car relay determines the amount of current that it can safely handle without overheating or malfunctioning. They are used in a variety of automotive applications to protect circuits and control heavy-load devices such as motors and pumps. They are available in a variety of shapes and sizes to suit the needs, thereby, it is important to choose the right one from a reputable manufacturer to ensure that it functions well and protects the circuits it controls.

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

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.

What Is The Difference Between Normally Open And Normally Closed Relay

There are two main types of relays: normally open (NO) and normally closed (NC). The difference between a normally open and normally closed relays lies in their default positions when no current is applied to the coil.

• A normally open relay has a set of contacts that are normally open or disconnected when the coil of the relay is de-energized (is not yet energized or in its relaxed state). When current is applied to the coil, it becomes magnetized and the movable contact is attracted to the fixed contact, closing the circuit and allowing current to flow through the contacts. This type of relay is often used to start or stop a circuit when a certain condition is met, such as when a button is pressed or a sensor is triggered.

• A normally closed relay, on the other hand, has a set of contacts that are normally closed, or connected, when the coil is de-energized (is not yet energized or in its relaxed state). When current is applied to the coil, it becomes magnetized and the movable contact is attracted away from the fixed contact, opening the circuit and interrupting the flow of current through the contacts. This type of relay is often used as a safety feature to automatically cut off power in the event of a malfunction or other emergency.

It’s important to note that both normally open and normally closed contact can be used to start or stop a circuit, depending on how they are wired and the specific requirements of the products. For example, a normally open relay could be used to start a circuit by closing the contacts when a button is pressed, while a normally closed relay could be used to stop a circuit by opening the contacts when a sensor is triggered.

In summary, the main difference between normally open and normally closed relays is the default physical position of the contacts when the coil is de-energized. A normally open relay has open contacts, while a normally closed relay has closed contacts. Both types of relays can be used to start or stop a circuit, depending on how they are wired and the specific requirements of the application.

Frequently Asked Questions (FAQs)

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