Differential circuit breaker: purpose, types, marking + selection tips

Vasily Borutsky
Checked by a specialist: Vasily Borutsky
Author: Victor Kitaev
Last update: May 2019

The differential switch action algorithm is based on providing reliable protection against possible leakage currents. For example, in cases of indirect contact with conductive elements or at moments of short-circuiting of live parts to the housing. The choice of protective device should be taken responsibly. Do you agree?

We will tell you how to correctly choose a differential circuit breaker, endowed with advanced protective functionality. In our article, we describe in detail the types of devices that can prevent a lot of threatening situations. Valuable recommendations are given to future buyers.

Differential Current Device Operation

Considering the standard design of RCDs (UDT), three main modules should be highlighted:

  1. Summing current transformer.
  2. Trip converter.
  3. Locking device for switching elements.

Current-carrying conductors of the current circuit are connected to the contacts of the summing transformer. Given Ohm's law, according to which the sum of all currents gives zero, the magnetic effect of the current-carrying conductors of the transformer is mutually compensated.

The magnetic field, causing due to the induction effect, the appearance of the voltage of the secondary winding of the transformer, is not formed. This state corresponds to the normal current flow conditions in the circuit.

Internal device UDT
UDT device: 1 - input circuit contacts; 2 - contacts of the output circuit; 3 - cock button; 4 - make contacts; 5 - summing transformer; 6 - secondary winding; 7 - tracking device; 8 - button "test"; 9 - test conductor

However, the formation of even a small leakage current violates this balance. The core region of the transformer is exposed to a residual magnetic field. As a result, the secondary winding produces voltage.

The release is naturally activated, converting the electrical quantity into mechanical action. Next, the differential current blocking device is triggered.

A similar protection technique is characterized as high-level, because the circuit is broken regardless of the mains voltage or the voltage of the auxiliary energy source. It is this principle of action that guarantees 100% protection in any circumstances.

The design of each differential current switch is usually equipped with a test key. The so-called “control button” is specially displayed on the front panel of the device so that users can check the operational readiness of the protective device.

Differential machine design
The test button is used to verify the health of the device. The usual use of the button is after the first installation of the device and its commissioning, as well as during maintenance

If you press the Test key, the mechanism of the device artificially generates a leakage current. In this case, a serviceable device is sure to work. Usually the “Test” button is used immediately after installing the machine in the circuit, the first time you connect electricity. Subsequently, they are tested according to the schedule, approximately once a quarter.

Types of residual current circuit breakers

The variety of circuit breakers is impressive. Thanks to such a variety, the possibilities of organizing effective protection in projects of any purpose are opened. Consider a few examples of the design of the RCD to evaluate all the existing advantages.

Standard Devices

The main purpose of standard devices, for example, the F, FH series, is to protect service personnel. Direct / indirect contact with live parts, risk of electric shock - such situations are reduced to zero when the F, FH series circuit breakers are used.

FH200 residual current device
A device from the ABB series of residual current circuit breakers manufactured by the F and FH series. A product from the category of economical, but quite effective products

The best choice for use in household and commercial applications. Instruments also provide fire protectionif there are risks of cable fire under long-term exposure to leakage current.

This type of device is designed for implementation in AC networks with minimal levels of high harmonics and the absence of constant voltage. The load current 16 - 63A, the stock of mechanical cyclicity - 20,000.

Another example of standard selective devices is the ABB DS series. They are designed for installation and operation in single-phase networks. WITH principle of selectivity will familiarize you with an article that we highly recommend reading.

The purpose of the DS series differential current circuit breakers is to organize protective circuits against overloads and short circuit. The modules provide a clear work of protective functions for accidental contact with live lines or equipment elements.

DS residual current devices
Selective action device is a product manufactured by ABB. Products like the DS serial modules have shown long-lasting flawless performance in practice and are therefore in demand

A distinctive feature of the DS series design is the presence of a visually detectable indication signaling the presence of leakage current. This is one of the designs of the protective device, due to which it is possible to prevent fire, to signal a violation of electrical insulation. Permissible load 6 - 40A. The cycle is 20,000.

The “home” differential circuit breaker of the AD series, BD is a product of the German company “Schneider Electric”, was developed, first of all, for implementation in the structure of household power networks.

The main purpose is to exclude electric shock to the physical body.Also, this type of protective device quite effectively and efficiently protects electrical equipment, cables, equipment.

Differential automatic devices
A series of devices specially designed for use in home (apartment) networks. This type of differential circuit breaker was designed by the German manufacturer Schneider Electric

The sensitivity of the machine for direct (indirect) contacts with parts of electrical equipment under voltage corresponds to the standard (30 mA). Standard sensitivity (100 - 300 mA) is also provided in case of detection of current leakage due to fires. A good solution for equipping residential buildings and office space.

Monoblock differential machines

Monoblock devices function in a complex manner, and this is their main difference from standard developments. They cover the whole range of protective functions that modern protection devices should have. True devices of standard design also provide users with wide functionality.

A striking example of residual current circuit breakers operating in an integrated functionality are products of the same Schneider Electric company. In particular, the models of the “Multi” series are load switches of selective and instantaneous action.

Construction Devices Multi
Another option for efficient and reliable devices developed as part of projects called “Multi”. Devices have a wide range of properties that provide protective functions.

Automata, depending on the model, are intended for installation in the distribution networks of administrative (household) buildings of industrial production.

These UDTs provide circuit breakage at leakage currents of 10 to 500 mA. A design feature is the ability to adjust to exclude accidental operations (lightning discharges, breakdown through a layer of dust, etc.).

Surge protectors

Perhaps, a separate type of devices should be considered as design developments similar to circuit breakers, the implementation of which provides protection against surge surges.

As a rule, this type of device is endowed with ultra-high speed, a sensitivity level of 10 - 30 mA in case of a trip upon contact with live surfaces. The same machines guarantee reliable protection of equipment from overcurrents.

Differential automatic machines of pulse protection
Devices designed for use in circuits where there is a risk of surge voltages. Differ in a little advanced functionality

The range of rated currents here is usually 6 - 63A at voltages of 230 - 440 volts. Switching capacity reaches a value of 4500A. Structurally available for power supply through 2 or 4 poles.

From the same series, but slightly modified, circuit breakers with the characteristic “A” are seen. A good example is the AD12M series, where the expansion of protective functionality is noted. Among the additions is the shutdown function in case of an increase in the mains voltage above 265 volts for 0.3 seconds.

It should also be noted that devices endowed with the characteristic “A” have significant differences from the performance of differential automata with the characteristic “AC”. The first option is able to respond to a continuously pulsating differential current and to a sinusoidal current.

Mobile residual current devices

Industry (foreign and domestic) produces another variety of automatic differential switches in the design of a mobile type. That is, we are talking about portable devices controlled by differential current.

Mobile protective device - socket
This design is typical for modern portable models. Mobile residual current protective devices recommended for residential applications

Such mobile modules are made in the form of a miniature unit, which is simply inserted into a household outlet. Meanwhile, this type of device is intended for use inside rooms belonging to the group of especially dangerous (with increased danger).

These devices are often installed as additional modules to existing ones. residual current circuit breakers.

This same type of device is a portable configuration, it is recommended to use it in domestic conditions to protect children and the elderly. As you know, the resistance of the body of young and old organisms is slightly different from the same size of a middle-aged human body.

Therefore, portable RCDs are made constructively as devices having an increased level of the trip setting. This setting value usually does not exceed 10 mA for mobile type devices.

Portable machines, for example, the UZO-DP series, are considered optimal protection for private urban and suburban real estate - cottages, country houses, garages, etc.

Marking UZO (UDT) on the case of devices

It should be noted that the case characteristic (symbols on the case) of modern devices shows almost complete information regarding the electromechanical and temperature parameters of devices.

Safety device marking
All information about performance, scope and even the best connection option is printed on the housing of the protective device in the form of a clear, easy to read marking

In fact, the user does not even need to refer to the accompanying documentation, since, knowing the notation, all information can be obtained by reading the information from the front of the case.

Among the designations, it is recommended to study a graph showing the characteristics of the machines with respect to the operating conditions: "A", "B", "AC", "F", which determines the sensitivity of the device to alternating and direct currents of various shapes.

The abbreviation designation of devices often reflects their typical and serial affiliation. For example, “AD12M” is a differential machine, the serial number is 12, upgraded. Or so: "VD63" - differential switch, 63 series.

True, there are models (usually imported) that have a somewhat confusing abbreviation, say - FH200. Here: the symbol F is the series of the device, H is the housing version, 200 is the serial number.

Or another example: a device designated by the abbreviation DS. The first character is understandable without a "translation" - differential. The second indicates that the device belongs to the category of selective devices.

The question of choosing between differential automaton and RCD requires detailed study. We recommend that you familiarize yourself with the material that analyzes their differences, the specifics of use, as well as advantages with disadvantages.

How to choose a differential current device?

Differential current devices are selected in the same way as they are, for example, with circuit breakers.

Selection of differential current devices
The choice of UDT. With the extensive information that is displayed on the front panel of the module, you can choose devices without difficulty directly at the place of purchase

That is, the choice is made on the basis of traditional criteria for the selection of electrical equipment of this type:

  1. Purpose of use.
  2. Compliance with load current.
  3. Response sensitivity criterion.
  4. Case execution.

For use in everyday living conditions, the choice is usually made by single-phase devices with characteristics “AC” or “A”. For use on domestic networks of residential buildings, it is better to take devices with a sensitivity of 10-30 mA (for touch) and 100 mA (fire protection and short circuit). Case execution - the most convenient for installation and in terms of operation.

It should be noted: the differential current device is always mounted in series with a circuit breaker.Therefore, the current characteristics of both devices must match or the rated current of the UDT must be higher.

Conclusions and useful video on the topic

You can find out even more interesting information about the device, types and principle of operation of diffavomats from the following video:

The residual current protective devices are in fact circuit breakers supplemented by a sensitive system for detecting current leakage.

It is imperative that such devices be equipped with power networks, the performance of which is associated with the risk of contact between people and live parts of the equipment. Schemes of modern execution by default involve the introduction of UDT.

Want to talk about how you selected a differential switch to protect your home or country network? Do you have useful information on a topic worth sharing with site visitors? Please write comments in the block form below, post a photo and ask questions.

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