Electrical distribution box. Riding step by step!

According to the NBR-5410 standard, all electrical installations must contain at least one Circuit Distribution Board (QDC), but unfortunately not even the electricians know how to do or where to start the assembly of a QDC, thinking about it we decided to teach how to perform the assembly of a distribution board step by step. Come on, guys!

Distribution box:

The distribution box, better known as circuit distribution board (QDC) is undoubtedly one of the most important parts in electrical installation since it is through the distribution board that all the energy of the installation passes.

The distribution board is responsible for containing all the necessary protection devices, and as its name says it has the objective of distributing all circuits to the points of use of the installation, to guarantee safety and good functioning, in addition to the distribution box prevents defects and accidents within the installation.

The circuits contained in the distribution box are properly separated, such as lighting circuit, circuit for general-purpose sockets (TUG), and individual circuits for specific use sockets, so that all circuits have maximum power to be dissipated .

All circuits inside the distribution box must be properly identified, to ensure the safety of the professional who will carry out maintenance, tests and inspections at the QDC and the users of the installation.

Assembly of distribution board step by step.

No matter what services we are going to develop in electrical installations, all of these services must always be in accordance with the standards, such as NBR 5410 – Low voltage electrical installations – and NR-10 – Safety in installations and services with electricity. Following the rules and correctly executing the electrical installations is the minimum that is expected of a professional in the World of Electrical.

As previously mentioned, the distribution board is where all protection devices are contained, both for circuits and for people, such as circuit breakers, surge protection devices (DPS) and residual differential switch (IDR), therefore, it is essential that all of them are properly dimensioned and installed according to the NBR-5410 standard for low voltage electrical installations.

Distribution board assembly:

Before carrying out the assembly, it is necessary to know which distribution box will be used, for this, it must be made the division of circuits, and the dimensioning of the protection components, such as the dimensioning of the circuit breakers and electrical cables.

QDC installation location:

According to the NBR-5410 standard, there are not many restrictions regarding the location of the distribution box installation, so the only requirement for the QDC is that it is not installed in places where the power distribution board (QDF) is locked, that is, difficult to access, apart from these situations the distribution board can be installed anywhere, according to the norm.

Below we show the image of a floor plan with the necessary indications of the locations that the circuit distribution board may or may not be installed.

Locations that may or may not be installed on the QDC.

Note that the image above does not indicate whether or not you can install the distribution box in the room, but due to aesthetics issues we do not recommend that you install the QDC in the room.

We recommend that the installation of the distribution board is done as close as possible to the meter, because the cables that are taken to the distribution box are the ones that carry greater current and are of greater thickness, thus the distance directly interferes in the dimensioning of the cables electrical.

Mounting the distribution board:

We will assemble a distribution board for a two-phase circuit (phase, phase and neutral) that contains a residual differential device, three surge protection devices and six circuit breakers, five of which are single-phase than the general circuit breaker which is bipolar.

We advise you to make sure that the conductors coming from the meter are not energized, so turn the circuit breaker off from the input standard before performing any service.

Step 1: First fix the components, so that the assembly is as organized as possible, then supply the general circuit breaker.

In this case, we will supply the general circuit breaker below, as shown in the image below. The circuit breaker is being powered from the bottom due to a matter of aesthetics and organization, but there is no correct polarity for the AC circuit breakers, they will work anyway.

Wiring diagram for a QDC. Energizing the general circuit breaker.

Step 2: The neutral conductor that comes directly from the meter is connected directly to the input of a DPS and immediately afterwards we drift to the input of the DR, in this case we feed the residual differential over the top, as shown below:

Wiring diagram for a QDC. Connecting the neutral cable to the DPS and DR.

It is important to note that the only restriction of the residual differential switch is the phase and neutral poles, that is, you can only connect the phase and neutral cables to the terminals specified in the device.

Step 3: After the phase conductors are disconnected by the general circuit breaker, the two remaining surge protection devices (DPS) and the residual differential (DR) will be supplied, that is, the cables are connected from the general circuit breaker output and derivatives for DPS´s and DR entries, as shown in the image below:

Wiring diagram for a QDC. Deriving the phase conductors.

Step 4: After supplying the DPS´s and the DR we will connect the outputs of the DPS´s on the ground bus and in this same bus we connect the grounding conductor, so that each circuit has a grounding conductor separately, as the indicated in the diagram below:

Wiring diagram for a QDC. Connecting the outputs of the DPS´s on the grounding bus.

Step 5: Now we will make the connections to supply the monopolar circuit breakers. For this we will use a comb bus to derive the residual differential switch outputs. In this case, we recommend using the comb bus, as it offers a better fixation on the terminals, is safer and still saves space.

Wiring diagram for a QDC. Energizing the circuit breakers of each circuit, using the comb bus.

Step 6: As soon as the comb bus is connected to the inputs of the circuit breakers, the phase cable is connected to the output terminals of each of the circuit breakers, which will be the phase conductor of each circuit. The diagram below shows how the phase cables of each circuit should be connected.

Wiring diagram for a QDC. Connecting the phase cables to the home circuit breakers.

Step 7: Each circuit must have a separate neutral cable, so we will connect a cable from the DR output and connect directly to the neutral bus. From then on we will connect the other neutral cables of the circuit to the neutral bus, as shown in the diagram below.

Wiring diagram for a QDC. Cable exiting the DR and connected to the neutral bus.

Final considerations:

As we can see the connections made, it is a distribution board for five circuits, so each of the circuits, has a circuit breaker and its respective grounding conductors and neutral conductors, which are protected by the general circuit breaker, DPS and DR. The image below shows the final wiring diagram of the switchboard.

Wiring diagram for a QDC. Complete wiring diagram.

So that you can perfectly understand the step by step of this assembly, we leave a video below performing this assembly and giving some tips that are essential during installation.

We finished this article and we hope to have helped you to clear all your doubts about how to assemble a distribution board! If you still have any doubts or curiosity about this matter, leave it in the comments and we will respond.