Magneto-thermal Circuit Breakers

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Circuit breakers protect against indirect contacts, they are the ones that protect the equipment connected to the installation. Depending on their location, a different nomenclature is used to name them, but they are always the same type of product:

• IGA (Automatic General Circuit Breaker) is a 32 or 40 A circuit breaker and is placed downstream (in front of) the differential switch, it protects all the circuits of the installation.
• PIA (Small Circuit Breaker) is installed downstream of the differential and each one protects a circuit of the installation.

Composition and operation of circuit-breakers

Circuit breakers consist internally of two parts, a thermal protection and a magnetic protection:

• Thermal protection: Protects against circuit overloads, the current passes through a bimetallic switch which, when heated, expands and hits the mechanism of the device to open the contact and disconnect it.
• Magnetic protection: It is in charge of protecting the circuit against short circuits, it consists of an electromagnet, it works in such a way that when a very high current circulates it generates a magnetic force, thus attracting a piece that opens the contact of the device.

Circuit breaker curves:

The circuit breaker must be duly chosen depending on its tripping curve, which depends on the number of times the In (Rated Current) is withstood, it will be used in one type of installation or another. The most common and most commonly used are:

B-curve: 3 to 5 times their In, they are used rather rarely, especially for long cabling distances.

Curve C: 5 to 10 times its In, most commonly used in the domestic environment.

Curve D: 10 to 20 times its In, mainly used for industry, where machinery is used.

What is the breaking capacity of a circuit breaker?

We call the breaking capacity of a circuit breaker the maximum current that it is capable of breaking. If the current generated by a short-circuit, for example, is higher than the breaking capacity, the circuit breaker will trip but current could continue to flow by means of an electric arc.

Possible causes for tripping the circuit breaker

By overloading: This is usually due to an excessive number of connected devices.

Short-circuit: Due to overheating of the conductors, a very high current is produced in a short period of time.

Resettable circuit breaker

This device can be automatically reset in the event of a transiently high current. If this current occurs again several times, it will open the contact and can only be reset manually.

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