What is the difference between an RCD from a differential automaton and what is better to use?

Vasily Borutsky
Checked by a specialist: Vasily Borutsky
Author: Tatyana Zakharova
Last update: April 2019

One of the steps of a home electrical device is to install protective equipment. It is mounted in an apartment electrical panel. In the event of an increased load or failure, the device promptly trips to protect the entire system or a separate circuit.

But before installation, you should find out what the difference between RCDs from a differential machine is in order to properly organize and secure the home network.

We offer to understand the functional features of switching devices, and find out in which situation, which is better to use. In the article, we identified the main criteria for the selection of electrical protective devices, and also described the specifics of their connection and operation.

The need for power protection

A home electrical system is a complex branched network consisting of many circuits - lighting, outlets, separate power and low-current ones. It includes all electrical installations that have to be used daily. The simplest among them are sockets and switches.

During the operation of home electrical appliances, unforeseen situations arise, the result of which is the failure of individual circuits, devices, as well as accidents.

The causes of trouble are the following phenomena:

  • excessive load on the power line;
  • leakage currents;
  • short circuits.

Overload can be encountered if you use new powerful equipment in an apartment with old wiring. The cable does not withstand the total load, overheats, melts and fails.

Thoughtful use of tees
A great example of the rash application of a Chinese-made extension cord without a fuse, coupled with tees.The simultaneous use of several devices on the same power line can cause fusion of contacts and insulation, as well as fire

The danger of leakage currents arises when the insulation of the electrical cables and devices becomes unusable, the installation is incorrectly made or the equipment is grounded.

If the current rises above 1.5 mA, the effect of electricity becomes noticeable, and more than 2 mA causes seizures.

Ignition of a power supply section
Irreversible consequences are also caused by a short circuit due to an unintentional connection of zero and phase. The result of the formation of an electric arc is the ignition of a separate section of the wiring, and often - of surrounding objects

To protect equipment, property, and most importantly - the life and health of residents, emergency shutdown devices are used. Without them, modern electrical wiring system in the apartment or private house considered inferior and dangerous.

Switching devices, load shedding

If the electrical system of an apartment or house is divided into separate circuits, it is recommended that each circuit line be equipped with a separate circuit breaker, and an RCD is installed at the output.

However, the connection options are much larger, so first you need to understand the difference between the RCD and the differential machine, and then already make the installation.

Circuit Breakers - Modified Plugs

When the variety of protective devices was out of the question, with excessive load on the line, “traffic jams” - the simplest emergency devices — were triggered.

Their functionality was improved and received circuit breakerswhich are triggered in two cases - when a short circuit occurs and when the load is close to critical.

Circuit breaker device
The design of the machine is simple: several functional modules are enclosed in a housing made of durable technoplastic. Outside, there is a chain closing / opening lever and a mounting groove for “landing” on a DIN rail (+)

In one switchboard there can be one or several switches, their number depends on the number of circuits serving the apartment or house.

The more individual lines, the easier it is to replace or repair electrical appliances. To install one device, you do not need to disconnect the entire network.

A prerequisite for assembling a home electrical network is machine connection. Switches operate quickly when the system is overloaded and due to a short circuit. The only thing they cannot protect from is leakage currents.

RCD - automatic protection devices

Exactly RCD is the device that automatically analyzes the current strength at the input / output and protects against leakage currents. The shape of the case, it looks like a circuit breaker, but works on a different principle.

Inside the housing there is a working device - a core with windings. The magnetic fluxes of the two windings are directed in opposite directions, which creates a balance. Thus, the magnetic force in the core is reduced to zero.

As soon as the leakage current occurs, the difference in the values ​​of the magnetic fluxes appears - the output value decreases.As a result of the interaction of the flows, the relay trips and breaks the circuit. Time interval of operation within 0.2-0.3 sec. This time is enough to save a human life.

RCD device
External distinctive features are the presence of additional terminals (the machine has 1 piece above and below), a test button, a wider front panel, and a different marking (+)

On the case you can see the marking 10 ... 500 mA. This indicates the rated leakage current. For home use, an RCD with a 30 mA rating is usually chosen.

Devices with a designation of 10 mA can come in handy if a separate circuit is displayed on the children's room or in the bathroom, where there is an increased level of humidity.

RCD protects against leakage currents, but it is useless with an increased load on the wires, and also does not help in any case with a short circuit. For this reason, two devices - an RCD and a circuit breaker - are always mounted in pairs.

Only together they will provide a full degree of protection, which must be present in every household electrical system.

Differential Automatic - Maximum Protection

When we talk about the fundamental difference between RCDs and differential automaton, we mean not a separately installed RCD device, but a pair of "RCD + switch".

The differential current circuit breaker (AVDT), in essence, is this pair, but combined in one housing.

Thus, it immediately performs three main functions:

  • protects against leakage currents;
  • prevents line overload;
  • instantly triggered by a short circuit.

Despite its small size, the device operates efficiently and quickly, but on one condition - if it is released under a reliable, established brand.

RCD and Difavtomat
If you do not know the nuances of the device and the symbols placed on the case, the difavtomat can be easily confused with an RCD. One of the hints is marking AVDT (+)

The technical documentation, which must be attached to the device, lists its characteristics. The designation of the most important indicators is printed on the case on the front side.

In addition to marking the name, the rated load current and leakage current are indicated here. The units of measurement are the same as for simple machines - mA.

At first glance, it may seem that the appearance of a difavtomat completely erases the initially existing “circuit breaker + RCD” scheme. However, there are many nuances that govern the choice of a particular solution, and as a result, both installation schemes are relevant and in demand.

Criteria for choosing electrical protection devices

We will try to figure out what is best for the house - an RCD or a differential machine, and consider various installation situations. Most often, factors such as the position of the device in the electrical panel, the nuances of connecting to power lines, the possibility of maintenance or replacement influence the choice.

Features of installation in an electrical panel

The electrical panel is a metal box, inside of which protection devices and an electric meter are usually located. The working panel to which the devices are attached is limited in size.

If there is an improvement in the power network and at the same time additional modules are installed, then there is a shortage of empty seats on the din rails. In this case, difavtomats are in a winning position.

Mounting Devices on a Din Rail
The arrangement on the din-rail of the pairs “automatic + RCD” (upper row) and difavtomatov (lower row). Obviously, lower devices take up less space. The difference will increase if the protection is designed for more circuits.

Modern equipment of apartments with electricity is focused on increasing the number of circuits. This is due to the emergence of a large number of powerful equipment, and with the division of the network into many lines. In such a situation, in the absence of additional space, the only reasonable solution is connecting difavtomatov.

When choosing devices, pay attention to devices occupying one module-place. Such models have already appeared on sale, but their cost is slightly higher than that of traditional ones.

The complexity of connecting wires

The main difference between the connection between the two indicated options is in the number of wires. Two separate devices in total have more terminals - 6 pieces, while the difavtomat has only four. The connection diagram is also different.

Instrument Switching Scheme
Comparative diagram of the installation and connection of the protective pair and difavtomat. The result of an emergency response and the reliability of the devices are the same, and the connection order of the wires is different

The diagram shows the wire switching well.

At connecting a pair of AB + RCD the layout is this:

  • phase wire is connected to terminal AB;
  • the output of the machine and the L-terminal of the RCD are connected by a jumper;
  • the output of the RCD phase is sent to electrical installations;
  • the neutral wire is connected only with an RCD - at the input with an N-terminal, at the output - it is sent to electrical installations.

In a difiltomat, connecting is much simpler. Jumpers are not needed, only phase and zero are connected to the corresponding terminals, and from the outputs are sent to the load.

What does this give the installer? Facilitates the connection process, reduces the number of wires, respectively, guarantees more order on the electrical panel.

How is the operation diagnosed?

If we consider devices from the middle price segment, then the advantages of the tandem "machine + RCD" are advantages. Suppose an emergency power outage occurred on one of the circuits.

It is difficult to determine the cause of the protection operation right away, since it can be a leakage current, a short circuit, or the total load that the wires could not handle.

The position of the levers on the machines
By the triggered RCD or machine, you can immediately see where to look for the cause. In the first case, there is a problem with insulation, in the second, an increased load or short circuit. The latter can be determined by additional features

If a difavtomat responded to a network failure, then the cause will have to be searched for longer. It is necessary to check all versions, and this will take more time and effort.

To simplify the diagnosis, it is recommended to purchase devices from a more expensive price segment - they are equipped with an additional indication indicating a possible problem.

What appliances are cheaper to buy and repair?

There are situations when the choice is based on value. For example, there is a budget beyond which there is no way to go. In this case, the total cost of all connected protection devices plays a decisive role.

At first glance, a larger number of devices is characterized by a higher price. In fact, everything is different: a universal difavtomat costs a round sum, and a set of other devices is economical.

Comparison of the cost of appliances
If you monitor the price tags of all designated machines, then it turns out that one difavtomat is almost two times more expensive than the set “AB + RCD”

It should be remembered that the number of lines is usually 3 or more, so the difference between purchases grows. If for one circuit, the acquisition of an AEDT is more expensive by just 1 thousand rubles, then for five circuits the difference in the amounts grows to 5 thousand rubles.

Thus, both difavtomaty, and RCD units with circuit breakers have their advantages and disadvantages. If AVDT win in compactness and ease of connection, then they clearly lose in the diagnosis and cost accounting.

Conclusions and useful video on the topic

In order to better navigate the protection devices and choose the right solution depending on the situation, we suggest watching thematic videos.

Interesting information about the principle of operation and installation of RCDs:

A few tips from a professional electrician:

What played a role in choosing a difavtomat:

As you can see, the topic of choosing an RCD or AVDT is being discussed for good reason: there are many points that speak in favor of both devices.In order to choose the best protection option, it is necessary to consider the conditions of installation and connection, as well as draw up a preliminary estimate.

Have something to supplement, or have questions about the topic? You can leave comments on the publication, participate in discussions and share your own experience in using RCDs and differential machines. The unit for communication is located below.

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Visitors Comments
  1. master zheka

    Yes, safety, exclusion of defeat email. shock - this is all right. RCD or difavtomat are good to use in ideal operating conditions of new wiring. But in practice, mainly in a different way. Most of the people live in houses where the wiring is old, and, of course, there is a leak. Add here a slight increase in humidity in the room - and the consumer receives a constant protection response, a tedious search for the reason for the shutdown (and does not find in 99 cases out of 100, because the wiring is hidden in most cases), ultimately removes the RCD from the circuit, leaving only machine.