What is normally open and normally closed in relay?

This will have to start from his construction, normally open to a load, normally closed to a load, turn on the power supply, normally closed contacts above the light will light up, the point of the relay normally closed contacts above the light off, normally open contacts above the light on.

COM is the common terminal, it and one of the NC is normally open, that is, always conductive connected together;

And another is normally closed, that is, there is no physical connection, as long as there is a trigger signal, normally open disconnect, normally closed conduction, which will achieve a weak power control of the role of strong electricity.

Public terminals and the opposite side of the same layer of terminals form normally open contacts, and the opposite side of the terminals form normally closed contacts.

Then the question arises, how do we distinguish between the normally open and normally closed points?

In fact, the relay contacts are not divided into primary and secondary, but divided into main contacts and auxiliary contacts. And the contacts of the main and auxiliary contacts do not necessarily have the same number of points, and they are usually selected according to the circuit requirements and the application environment.

The main contact of a relay is usually used to open or close a circuit, for example, the main contact of an electromagnetic relay, which is widely used in low-voltage control systems, is used for this purpose. Auxiliary contacts, on the other hand, are mainly used to control circuits, for example, to perform operations such as self-locking, logic changeover and state memorization.

As for contactors, the main contacts are indeed larger than the auxiliary contacts. The main contacts are mainly used to pass load current while the auxiliary contacts are used to control the circuit. This is mainly due to the fact that contactors are usually used to control larger power loads and their main contacts need to carry a larger current. Auxiliary contacts, on the other hand, are mainly used to drive larger loads with lower currents and therefore do not require oversized contacts.

Although the main and auxiliary contacts of contactors and relays have some similarities in their use, their structures and functions are actually very different. For specific use, it is necessary to select the appropriate type and size of contact according to the specific situation.

And there are other test methods for you

Firstly, Test with a multimeter

When using a multimeter to test the relay front and rear contacts, you can measure the switching state and resistance value of the relay through the multimeter to judge the relay front and rear contacts.

      - Set the multimeter to "resistance", and connect the test leads to the two contacts of the relay;

      - Observe the resistance value shown on the multimeter, if it is shown as infinity, it means that the relay is in the state of disconnection, that is, before and after the contact is disconnected; if it is shown as the resistance value, it means that the relay is in the state of closure, that is, before and after the contact is connected.

Second, directly observe the relay leads

Another way to determine the relay before and after the contact is to directly observe the relay leads. In the relay lead area, the front and rear contacts are usually marked out, and you can judge the front and rear contacts of the relay by observing whether the contacts are connected.

The specific steps are as follows:

1. Remove the relay and observe the relay lead area;

2. Find the leads labeled "COM" and "NO" or "NC", "COM" is usually the middle lead, "NO" is the normally open lead, "NC" is normally closed lead;

3. Judge the front and rear contacts of the relay by observing whether the leads are connected to each other.

Third, according to the relay specification judgment

Each relay has a specification, which contains the relay model, parameters, lead identification and other information. In the relay specifications, usually marked before and after the relay contact position, you can judge the relay before and after the contact according to the specifications.

The specific operation steps are as follows:

1) Find the relay specification, find the relay model, lead identification and other information;

2) Judge the relay front and rear contacts according to the position of the front and rear contacts indicated in the specification.

When we use the relay in our daily life need to pay attention to the following

•  When checking the front and rear contacts, the power should be disconnected first to avoid the danger of electric shock.
• If abnormalities are found in the front and rear contacts, such as poor contact, etc., the relay should be repaired or replaced in time.
• Keep hands dry and avoid electrified operation to avoid electric shock accident.   

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