The circuit distribution board (QDC) is the heart of the electrical installation because it is in the QDC that we find all protection devices, in addition, it is in the QDC that the installation circuits are distributed. A common question about electrical installations is whether a two-story home needs more than one QDC? This is a common question for electricians and for this reason we will show in accordance with the standard whether it is necessary to have QDC for each floor of the house.
What is QDC?
The circuit distribution board (QDC) is undoubtedly one of the most important parts in electrical installation since it is in the distribution boards that all the electrical energy of the installation passes.
The distribution board is responsible for storing the necessary protection devices for the electrical installation, and as the name says the circuit distribution board aims to distribute all circuits to the points of use of the installation, to ensure safety and the proper functioning, in addition, the QDC avoids eventual accidents in the installation.
As an example of protection devices located in the QDC, we can mention circuit breakers, surge protection devices (DPS) and residual differential switch (IDR). It is essential that all protection devices are properly dimensioned and installed according to the NBR 5410 standard for low voltage electrical installations.
The circuits in the switchboard are properly separated, such as the lighting circuit, circuit for general-purpose sockets (TUG), and individual circuits for specific use sockets (TUE) etc. All circuits inside the QDC must be properly identified, to ensure the safety of the professional who will perform maintenance and of the users of the installation, in addition to facilitating inspections at the distribution board.
Distribution board per floor – Mandatory
To know the rules on the circuit distribution board, we have to consult the NBR 5410 standard. In the NBR 5410 standard, there are several items that deal with distribution boards, and we know that the installation must have at least one QDC, but there is only one item that speaks of the requirement of more than one distribution board.
Item 126.96.36.199 says that: when the installation has more than one supply, for example public network and local generation, photovoltaic systems and others, the distribution associated specifically with each one must be arranged separately and clearly differentiated from the others. In particular, it is not allowed that components linked specifically to a given supply share, with elements from another supply, distribution boards and lines, including the boxes of those lines.
The NBR-5410 standard never deals with installations with more than one floor. So as a rule, the installation must have at least one distribution board and can have one more distribution board if the installation designer finds an advantage.
Distribution board per floor – Advantages
The NBR-5410 standard does not require having a QDC for each floor of the floor, but having more than one distribution board has some advantages, which are:
First advantage: the circuits from the circuit breaker to the sockets are smaller and this generates savings in the cables, being necessary only to take a cable with a larger diameter to the circuit distribution board on the second floor so that the respective circuits are properly distributed.
Second advantage: many high-power loads such as air conditioning and shower are located next to the dorms that are usually on the second floor of the residences, so with QDC closer to the high-power circuit, you can reduce the length of the larger diameter cables generating savings.
Third advantage: for security reasons, it is important that protective devices are easily accessible, and having a QDC on the first floor is less secure than having a QDC per floor.
We know the importance of the distribution board in the resistances and how it is fundamental for the proper functioning of the electrical installation. Below we leave a video from the World of Electrical on how to assemble a distribution board .