How to properly install an RCD in an electrical panel: before the machine or after

When installing a new or modernizing an old shield with a new machine, it is necessary to install a residual current device. The device protects the line from overloads, short circuits and prevents household appliances from breaking down. Some masters cannot decide whether to install an RCD before or after the machine. Popular schemes will help you choose a connection method.

The principle of operation of the RCD, differences from the difavtomat

The requirements of the PUE indicate the need for the installation of protective equipment. It provides protection against electric shock, breakdown of the insulation coating of the cable. The RCD can be connected to 2 wires in a network with a voltage of 220 V and to 4 wires in a network of 380 V.

The disadvantage of the device is the impossibility of detecting overload or short circuit. The automatic switch will additionally protect it. The difference between the devices is the response of the RCD to the current imbalance of the phase and zero with a nominal value of 10-30 mA. The device does not recognize overcurrents and may even catch fire under their influence.

The difavtomat normally operates at a current strength of up to 16 A, turns off the line in case of leaks. Unlike an RCD, it has a time-current characteristic, on which the shutdown speed depends.

A circuit breaker with an electromagnetic release is triggered when the current value is exceeded by 5-10 times.

Features of the integrated work of protective devices

To understand how to install an RCD - after or before the machine, you need to understand the functionality of the installation. A clear example would be a system of an accounting device, a residual current device, a difavtomat, thrown on one line.

The voltage from the transformer will pass through the RCD and the meter, being supplied to the outlets. If there is no protection, the disconnect device burns out. The absence of a release in front of the meter will also lead to a fire in the line. The best option is a protective device on both sides.

According to the requirements of the PUE, two-pole modifications of machines are installed before the metering device. It is not necessary to put it in front of it - it is better to protect the line from the RCD to the consumers.

Installing an RCD in front of the machine or after

The device responsible for disconnecting the line does not react to overcurrents, therefore it does not work in case of short circuits and overloads. A joint connection with a difavtomat will prevent these situations.

Since the fault current exceeds the rated current, the internal components of the device are damaged, the contacts burn out. Models without built-in protective elements must be installed together with circuit breakers that will eliminate the effects of overloads and short circuits. In this case, the current of the circuit breaker should not exceed the current rating of the RCD. For example, the latter responds to 40 A. The optimal switch for him is 36 A.

Connection diagrams of an RCD with a switch

You need to connect protective equipment to two cables. According to the first, the load current will go, according to the second, it will be directed to the external circuit from consumers. In order not to think, an RCD should be installed before or after the machine, you should use popular schemes.

For several groups of difavtomats - one RCD

Clause 7.1.79 of the PUE allows you to organize the protection of several lines using an RCD. The device must be placed on top, then switches for consumer groups.In case of short circuits, the current passes through the RCD to the group circuit breaker, then to the power cable and to the consumer. If the rating of the devices is selected correctly, not one of them will be damaged.

The advantages of implementing the scheme include savings in finances and space in the switchboard. The minus of the connection is the disconnection of all groups after the RCD is triggered.

Installation of an RCD before the machine

The scheme provides for installation in the following sequence:

1. Safety shutdown device.
2. Difautomat.
3. Power wire.
4. Consumer.

In the presence of damage, the short-circuit current flows through the RCD until the circuit breaker stops.

RCD after the machine

The assembly of the system is carried out according to the principle;

• switch - two-pole or feeder;
• counter;
• RCD;
• machines depending on the number of lines.

This option is correct, since it is easy to understand how to turn off the machine and apply input to its terminals. Despite the fact that RCDs break more often, they are easier to replace.

At the moment of a short circuit, the current will pass from the switch to the RCD, then to the power wire, then to the consumer. The switch stops and the protective device remains intact.

To prevent overloading, a second difavtomat can be installed between the meter and the RCD.

Connecting an RCD to a group of machines

A similar circuit is assembled in a three-phase switchboard, where are located:

• 3 three-phase difavtomats;
• three-phase RCD;
• 2 single-phase RCDs;
• 4 single-phase single-pole circuit breakers.

From the first automatic input, the voltage will go to the second three-phase unit along the upper terminals. From the same device, one phase will go to a single-phase RCD, the second to the next.

Single-phase protection devices have two poles, difavtomats - one. For the system to work without failures, it is required not to connect the working zero after it. For this reason, a zero bus must be installed after each protective device.

In the presence of two-pole machines, a separate zero bus is not installed. When two zeros are combined, a false alarm is possible.

The first single-pole RCD is connected to the differential automatic devices No. 1 and No. 3, the second - to No. 2 and No. 4. The load is applied to the lower terminals.

The grounding bus is common, but it must be installed separately. Three phases with a working zero are brought to the input device. It is connected to a common zero, and then diverted to all RCDs. After device No. 1 it goes to a three-phase load, after the other single-phase devices - to each bus.

The wire for PEN and PE is not separated - earth, zero and 3 phases go to the shield.

Where to install an RCD

To determine where to install the protective shutdown device, you need to remember the speed of current flow through the wires. It is equal to the speed of light - 300 thousand km / sec. In a standard C 16 machine, the turn-on time with the passage of currents 5 × In (80 A) will be 0.02 sec. The distance that he will cover is 6000 km.

In the event of a short circuit, the current will completely pass through the hitch difavtomat - RCD - cable - socket. In this case, the switch does not work instantly, as a result of which the insulation melts and the socket contacts burn out.

The RCD does not fail, since a short circuit is an inertial reaction. The time of 0.02 seconds is simply not enough to melt the insulation coating and damage the parts. Even taking into account the breaking capacity, the protective devices will function properly regardless of the place of installation:

• Automatic machine - RCD. The phase is fed using a jumper, and zero is fed directly to the protective device. The wire to the sockets is connected to the device and the PE-bus.
• RCD - automatic machine. The wire connects to the sockets through different paths. Phase goes to the machine, zero - to the protection device or zero bus.

Thus, there is no difference where the RCD was installed - before or after the difavtomat.

Machine denomination

On the case of any device, a nominal value is indicated - the value of the maximum long-term current that passes through the device without harm. This parameter is safe for current commutation.

To ensure the protection of the RCD itself, it is required to supply a difavtomat with a rating similar to or 1 more than the rating of the device. In the presence of a machine with a rating of 16 A, the RCD should be about 25 A. Such a current reserve will be sufficient to prevent the flow of energy when the load rises.

The machine trips when a current appears 13% more than the nominal: a 16 A modification will work at a current of 18 A. If the RCD is equal, the contacts may heat up. To select the rating of a system with several difavtomats, you need to sum them up and select an RCD with a large indicator.

The nuances of installing a protective device

Connecting an RCD in an apartment or house requires compliance with several rules:

• For several groups of consumers, you need to install one RCD and individual machines.
• If there are several RCDs, each of them will need a zero bus at the output.
• The TN-C system does not need to be zeroed.
• For "wet groups" it is mandatory to install a protective device with a trip rating of 10 mA.
• The 30 mA devices are suitable for water powered household appliances.
• The zero terminal is located on the right of the device and is marked with the letter N. It should not be confused with the phase (index L).
• Input can be made at the bottom or top terminals.
• The classical scheme is realized by means of the upper input and the lower output.
• For each RCD, a personal zero block is needed, to which all working neutrals are connected.
• For a line with ripple currents, type A devices are required.

You can check the health of the system by pressing the "Test" button.

A protective shutdown device is needed to protect against overloads, short circuits. Due to the absence of a reaction to overcurrents, it is installed in combination with a difavtomat. Connection diagrams allow devices to be installed in any order. The only condition is the choice of the appropriate denomination.