Differential Circuit Breakers

What is a differential circuit breaker intended for?

Serving as a protective piece in an electrical panel, the differential circuit breaker is a device which, in addition to protecting the equipment of an installation against short circuits and overcurrents, also protects individuals from any risk of electrocution. 

Its main role is to constantly monitor earth leakage currents, i.e., the isolation of cables and electrical receivers. In other words, it continuously compares the incoming current and the outgoing current in an electrical equipment. If the two are different, the differential circuit breaker detects an anomaly and then controls the isolation of the faulty equipment from the electrical network by triggering it. 

Difference between circuit breaker and differential circuit breaker?

Simply put, the circuit breaker protects the installation while the differential circuit breaker protects the installation AND the individuals.

The circuit breaker is equipped with a cut-off device and a tripping member which detects and controls the protection device. It then protects the equipment against short circuits (magnetic protection) and electrical overloads (thermal protection). The whole offer of One-Elec circuit breakers

The differential circuit breaker integrates the same components and protects the installation, but it also integrates a function for monitoring earth leakage currents which can be dangerous for individuals. An intensity of 30 mA is the threshold for respiratory paralysis and 40 mA is the considered threshold for irreversible cardiac fibrillation. 

Circuit breaker or differential switch, what's the difference?

The differentia circuit breaker protects property AND individuals while the differential switch protects only individuals. It must be associated with a divisional circuit breaker to ensure the protection of property.

The different types of differential circuit breaker?

All the circuits of an electrical installation must be protected by one or more residual differential devices (RCD) of which the differential circuit breaker is part. The NFC15-100 standard defines the number and type for all BT installations, regardless of the field of activity, residential or commercial buildings, industrial, agricultural or public facilities, and so on.

The type of differential circuit breaker depends on the equipment and circuits to be protected.

Differential circuit breaker type A

Type A is designed to detect leakage currents alternating AND continuous. It is mandatory to protect the equipment creating direct current such as the washing machine, the stove or the cooking plates. Type A is also mandatory to protect charging sockets for electric vehicles. The NFC15-100 standard requires that these devices be connected to a dedicated circuit protected by a type A differential switch, with a sensitivity of 30 mA with a maximum of 8 circuits per differential.

AC type differential circuit breaker

The AC type only detects the leaks of alternating current. That is why it is recommended to protect standard electrical equipment and circuits, such as lighting, electrical outlets, the oven, the refrigerator or the VMC. 

SI type differential circuit breaker

The SI type (super immunity) system is recommended for installations with loads sensitive to power outages and risks of inadvertent triggering such as computers and certain lighting systems such as electronic ballasts. Mainly used in industry, this type of differential circuit breaker is also particularly suitable for installations in the presence of harmonics on the electrical network and DC component sources such as diodes, diode bridges or switching power supplies. The differential circuit breaker is recommended here as a specific starting point to ensure service continuity.

Differential circuit breaker type B

This type of differential circuit breaker is designed for three-phase powered applications. It is required when Class 1 equipment is likely to produce DC component fault currents (speed regulator and variable speed drive, inverter, battery chargers, emergency power supplies).

The different sensitivity thresholds of the differential circuit breaker?

It is important to differentiate between caliber and sensitivity. The rating, expressed in amperes (A), corresponds to the threshold beyond which the circuit breaker automatically trips to de-energize the circuit and protect it from an overload or a short circuit. 

The sensitivity, expressed in milliampere (mA), corresponds to the detected difference in intensity between the phase and the neutral beyond which the circuit breaker trips to protect individuals from an electrical risk.  For domestic electrical installations, this sensitivity is set at 30 mA by the NFC 15-100 standard. 

Depending on the types of use, there are also differential circuit breakers with a sensitivity of 300 and 500 mA. In the industrial and tertiary fields, the notion of continuity of exploitation is very important and it can be penalizing to have untimely triggering of the 30 mA DDR on machines or safety lighting units, for example. However, in the case of aging installations, certain leakage currents can be produced at startup, without endangering the life of a person, the connections of the connected circuits being inaccessible. In this case, it is possible to install differential circuit breakers with a sensitivity of 300 mA. However, this does not exempt from a 30 mA DDR as long as individuals are potentially in contact with the equipment. The 300 mA DDR then remains the last barrier in the event of failure of the other 30 mA DDRs. This is the game of selectivity.

For more details, read our article: How to choose a differential circuit breaker