All you need to know about relays and how to use them properly

A relay is a device that allows connecting a circuit breaker to a current circuit. This is a fundamental component of an electrical circuit, and has been in use for a long time. In fact, relays were already used at the time of the telegraph, even though they were used for a different purpose.

Today, a large number of these devices is available on the market and can be divided into three different generations. Beware: the term generation refers to the shapes, the dimensions and the functions, and not necessarily to the age of the relay itself.


relays and techncian


Relay: first, second and third generation


First generation – These relays are the biggest instruments that can only be put into operation by a high-energy system. For this reason, they are very much used for electric lighting systems.

Second generation – These relays, however, have smaller dimensions and are characterized by a high efficiency that is generated by a relatively low current. Many of them are used in the medical field and in a series of electrical devices.

Finally, when we talk about third generation relays, we are talking about a more developed version of the previous models, characterized by a greater performance and, above all, by the fact that they can be programmed in advance. Programming a relay means that you can perform a greater number of tasks while maintaining efficiency at all times.


Relay: what is it for?


The relay is mainly used as a key element when connecting a circuit breaker to a large circuit or when, always within an electrical circuit, you want to look for a system to turn a lamp on or off alternatively, i.e. without using the classic switch.
A relay, in fact, is able to open or close a circuit via an electric impulse. Basically, relays work on a change of current: the relay, in fact, deviates the current flow without interrupting it, thus allowing the current to flow to another circuit. Moreover, we should specify that, as we have previously mentioned, apart from the three different generations of relays, there are also further classifications that frame the relays on a series of physical and electrical parameters.

However, from a technical point of view, relays can always be considered similar, i.e. characterized by three main elements: a coil, a toothed wheel and an electrical contact. When the coil is operated, an electromagnetic field is generated that moves the toothed wheel which will actuate the electrical contact by connecting to the switch (or the switches in the case of a multi-contact relay) to open or close the circuit.


Types of relays on the market

Relay step by step


A classic example of this kind relay is what can be found in apartments where a single light point can be switched on or off by multiple switches. In this case we refer to a step-by-step relay, one of the most classic relays, in use for a very long time in those rooms where it is necessary to control a light spot from different areas the room.

These solutions can be found in very long corridors or in multiple output halls that may, therefore, require the ignition on one side of the room and the powering off on the opposite side.

The mechanism of this type of relay is not complex at all. Like any another relay, the elements that allow it to operate are: the coil, the toothed wheel and the contact.

In this case, the coil is connected to the copper of the electrical wires and when the switch is pressed, an electromagnetic field is created allowing the coil to move by making a click on the toothed wheel. This trigger will allow you to activate or close the contact as appropriate: when the light is on, changing the toothed wheel position will cause the contact to close by turning the light off and vice versa.


The recycle relay


The so-called recycle relay is very common in apartments. It does not only allow to turn on and off a light spot from different switches of the room, but allows you to handle more light bulbs in the same light spot. This means, you can turn on one rather than the other, always from different parts of the room.

A recycle relay, to operate, features a number of additional contacts, which allow handling power in many different ways. In addition, the recycle relay allows you to control several light points within the same room and to manage various light bulbs on the same chandelier.


Timed relay and relay with a dimmer


Among the most modern relay models, there are the timed or dimmed ones.

The first allows you to turn on, from different parts of the room a light, but you won’t be able to control the shutdown that is automatic and takes place after a certain time depending on the settings and the type of relay.

Finally, the relays with a dimmer, allow to turn on and off a certain lamp by choosing the lighting level: these are modern models which, however, can be used only with certain types of lamps, the so-called dimmable lamps.

To know more read this > Dimmable led bulbs: how to correctly choose and install a dimmer


As we have previously mentioned, the structure of a relay is very simple and installing it within a circuit is equally simple. It goes without saying that every intervention on an electrical circuit must be carried out without current, to avoid even fatal risks.

Once the current is disconnected then you can install the relay simply by connecting the wires between the lamp and the relay.

Very often, different relays come with an instruction sheet where wiring and threading modes are indicated, i.e. the diagram of a circuit to which refer to make the connections.

If on the one hand, the number of contacts can be different, the connection diagrams are always very similar. As a matter of fact, one of the contacts must be always connected to the coil while the others have to be connected to the lamps and to the switch.

However, you always have to pay attention to the correct correspondence between the connected wires: this is an electrical circuit and a wrong connection can lead to a power failure or to a short-circuit. For this reason, it is always a good idea to pay close attention.


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