How to assemble a residential distribution board?

Do you know where the “heart” of your electrical installation is? that’s right, every installation has or at least should have, which is exactly the circuit distribution board the “heart” of your electrical installation. It is there that protection devices such as circuit breaker, DPS and DR are found. Thinking about the importance of the distribution board and the difficulty and doubts related to the QDC, we prepared this article, explaining in detail how to set up a residential distribution board, come on guys!

What is the distribution board?

The switchboard is mandatory in all electrical installations, as it is where the protection devices of a residential, industrial, commercial, etc. electrical installation are located. The distribution board is responsible for storing, protecting the protection devices and distributes all the circuits in the installation.

We can highlight that the distribution board is also known by many people as a general board, circuit breaker board and QDC (circuit distribution board). The distribution board can be found in PVC or metallic, in homes the most common is PVC, as it is cheaper. The iron QDC is more used in industry and in the assembly of controls, both the PVC and metallic distribution boards are found to be embedded and overlapped.

What are protection devices?

The protection devices are responsible for protecting your home from any problems such as electrical leakage, short circuit and overvoltages. The devices responsible for this protection are circuit breaker, DR (residual differential) and DPS (surge protection devices), they are the main components of a distribution board.

Components of a switchboard.

The main components of a switchboard are neutral and ground busbars, DIN rail, circuit breaker, DR (residual differential) and DPS (surge protection devices). There are other components such as, for example, contactor, relay, multimeter, among others, but which are not widely used in homes.

Circuit breakers

Circuit breakers are devices that protect against short circuit or overload, being essential to prevent accidents and even fires. There are different models of circuit breakers such as DIN and NEMA, which can be monopolar, bipolar or tripolar.

Circuit breakers also have as characteristic and fundamental factor for their design certain curves, which basically define their application, that is, the loads they will be connected to, for example, lighting circuit, sockets, motors, air conditioning, among others. The circuit breaker curves are B, C and D, and there are no curve A circuit breakers, one of the main reasons is not to be confused with the electrical current measurement unit, the Ampére.

DR (residual differential)

The DR  is responsible for protecting against electrical current leakage, thus protecting against electric shock. There are two types of DR, which are the IDR (Residual Differential Switch) and DDR (Residual Differential Circuit Breaker). The DR also have curves B, C and D, and several models such as bipolar, tripolar and tetrapolar.

DPS (surge protection devices)

The DPS is an electrical surge protection device, important for protecting electrical and electronic equipment. Electrical outbreaks occur because of lightning strikes that affect electrical networks and anomalies in the electrical network, such as the activation of large motors.

Din rail and neutral and ground busbars

The DIN rail is used to fix the protection devices. Neutral and ground busbars are the safest and most organized way of distributing electrical conductors and interconnect all conductors at a single point, thus facilitating future maintenance and ensuring that all conductors are securely fixed.

How to assemble a distribution board?

After all the explanations, let’s set up a distribution board. Before starting the installation of a switchboard, it is necessary to design the protection devices (circuit breaker, DR and DPS) and electrical conductors (wire or cable). To do the sizing, it is necessary to basically apply the ohm law and consult the tables of NBR-5410.

Assembly of the distribution board: Step by step.

It is important to note that the example below has not been properly  designed for protection devices and electrical conductors, as the purpose of this content is only the assembly and installation of the elements and not their respective dimensions.

The components used in this distribution board were a bipolar DIN type circuit breaker, three DPS, an IDR, five monopolar DIN type circuit breakers, neutral and ground busbars, DIN type rail and a biphasic comb busbar. So let’s go to the assembly.

Main components of a distribution board.

For your safety, first turn off the breaker of the energy meter and make sure that no one will turn on the breaker.

The following installation has a line voltage of 220 V, where the meter box exits four conductors, the neutral, earth and the two phases, which must be taken to the distribution board, located inside the building. All installation circuits are single-phase, with a balance between phases. Generally the conductor of the phase is black or red, in this installation the phase conductors are black, which must be connected to the upper terminals of the bipolar circuit breaker, as we can see in the image below:

Connecting the electrical conductors to the bipolar circuit breaker.

The neutral conductor must be connected directly to the lower terminal of the DPS and then it must be plated from the DPS to the lower terminal N of the IDR, remembering that the gauge of the jumpers must be the same as the neutral cable with the largest gauge.

Connecting the neutral electrical conductor in parallel of the DPS and DR.

Now, from the lower terminal (B) of the bipolar circuit breaker, make a jumper with the conductor until the lower terminal of the second DPS, after that make a jumper from the second DPS to the lower terminal (B) of the IDR. Then make a jumper from the lower terminal (A) of the bipolar circuit breaker to the lower terminal of the third DPS, then immediately make a jumper from the third DPS to the lower terminal (B) of the IDR, as shown in the image.

Parallel connection between protection devices.

Parallel connection of the circuit breaker with DPS and DR.

For the grounding conductors, the DPS must be connected all the way to the grounding bus. To do this, separate three green conductors and connect to the upper terminals of the DPS and take the conductor to the grounding bus. Also connect the main electrical conductor of the grounding loop.

Connection of DPS grounding on the bus.

In this distribution board, a bipolar circuit breaker was used as a general and a tetrapolar IDR, but we want the 127v circuit divisions to use monopolar circuit breakers to protect the devices. To achieve this, we use a two-phase comb bus, which must be connected to the two upper outputs of the IDR, where the connection of the lower phase conductors was made. The biphasic comb busbar will enable balanced connection in all monopolar circuit breakers, after which the electrical conductors that go to the circuits such as lamps, sockets, shower and so on can be connected.