A thermal relay is a device designed to protect motors and electrical installations from overloads and overheating which may cause damage to equipment, as well as power cuts and damage to the supply. It is a good way of keeping motors and electrical installations in good condition, as well as prolonging their life and giving you peace of mind.

How does a thermal relay work?

An electricity thermal relay is based on a bimetallic plate (iron, nickel and brass are usually used). This plate identifies any possible internal fluctuations in electricity and temperature as it reacts by expanding.

When the plate expands, the electrical current is automatically cut off. The supply does not return until the plate cools down and recovers its position.

Thermal relays can operate with both alternating current and direct current. Depending on the complexity of the model, they can be adjusted to modifiable parameters, enabling the system to be more accurate, to be suitable for specific circumstances and to increase the safety of the surrounding area. They can also be configured to make the recovery of supply manual or automatic (once the plate has cooled down).

We would also like to point out that there are already models that can be operated remotely, making operation and maintenance much easier.

What is a thermal relay for?

Here are some of the most important functions of a thermal relay:

• It protects motors and electrical installations from overloading and overheating. It automatically cuts off the electricity supply when a risk is detected. This makes it possible to locate the fault more quickly, so as to reduce the time it takes to repair the potential problem and enable the motor to operate safely again.
• It not only protects the equipment, it also protects the power supply.
• It provides an ongoing test for electrical installations to detect problems when operating. This means that you can anticipate a breakdown and the possible consequences before it happens.
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• It prolongs the useful life of the motor or electrical installation by taking care of its components and preventing them from having to be replaced. In the long run, it represents a considerable saving.
• It increases safety not only for the operation of the engine or the electrical installation but also when it is being handled, as well as providing protection for people working in the area.
• It avoids shutdowns in production systems.
• They are very useful in solar and wind installations as they protect them and prevent breakdowns.

What are the different types of thermal relay?

As we pointed out above, there are thermal relays for alternating and direct current, as well as different models with advanced functionalities. But they can also be classified in accordance with their function:

Differential thermal relay

This is suitable for automated industrial panels. It detects power cuts and imbalances between phases.

Compensated thermal relay

The advantage is that the ambient temperature does not influence its operation because there is a protective film which isolates the bimetallic plate from exterior ambient conditions. They are especially useful in contexts where there are extreme temperatures (very cold or very hot).

Tripolar thermal relay

They are the least complex and there is no differential between phases, which is why they are the most common. They can be adapted to single-phase, two-phase and three-phase systems and can be adapted to different electrical panels.

The thermal relay in your home

The benefits described above mean that the relay is a guarantee of protection for the electrical installation in your home. It is usually placed after the contactor, so the choice of thermal relay model will depend on the type of contactor and the characteristics of your electrical installation and type of home.

The thermal relay in a solar system

Another specific application of thermal relays is in solar installations. They should be connected on the positive pole of the panel and on the negative pole to the inverter, while the neutral pole should be connected to the earth. The aim is to ensure that the generation of the photovoltaic installation does not exceed a certain voltage (usually 330V). If this happens, the current is diverted to the earth connection.

As in the previous case, the thermal relay model should be adapted to the characteristics of the photovoltaic installation it will be attached to.

Breakdowns in your electrical installation

Endesa recommends that a professional should frequently check the electrical installation to ensure that it is correctly maintained so that it works properly.

If there is a power cut in your home and you have a thermal relay, the devise will enable you to check whether this is due to an overload or overheating. If this is not the case, Endesa offers you a 360 Electricity Protection maintenance service, with twice-yearly repair services for the electrical installation in your home and payment protection insurance for your electricity bills.