This guide presents and illustrates all the best practices to be applied in constructing low voltage distribution boards by the IEC 61439-1 and -2 standards. Using these rules means strict compliance, not only with the applicable regulations and standards but also with the manufacturers’ recommendations.
About this technical guide
This guide has been updated to consider recent changes in standards and the latest technological advances in the assembly and installation of switchboards. It is based on the experience acquired by Schneider Electric and its customers over many years.
It is intended to be used by panel builders in the factory and on-site and design engineers to integrate design rules.
It is structured according to the logical procedure for constructing panels, from the reception of the components in the workshop to the transport and installation of the complete discussion on site.
Power distribution bar
Energy is distributed in distribution boards through the following means:
The main bus bar distributes the energy horizontally between the different columns of the panel. It can be installed on the top, middle, or bottom of the switchboard, depending on the type of switchboard, customer specifications, and local practices.
Bus bars are connected to the main bus. They provide power to outgoing devices.
The following should be considered when choosing a power bus:
Environmental characteristics of the panel (ambient temperature, IP protection degree, contamination),
Type of panel installed concerning the validation test,
Customer power supply characteristics: top, middle or bottom,
The rated short circuit current: I CW.
The installation of a power busbar consists of the following steps:
Select the material of the busbar,
Dimension (section of bars, number of bars per phase) and define their position in the distribution board according to the incoming devices of the customer,
Install it according to the creepage distances and clearance of the standard,
Hold it following good practice.
Protection and safety of people
The installation must guarantee the protection of people:
Against direct contact by installing the appropriate internal partitions (forms) or installing live parts out of reach.
Against indirect contact by creating an equipotential connection inside the panel (PE / PEN protective conductor and grounding of the grounding electrode conductors).
The current of a power busbar is measured using a current transformer (CT), such as a busbar pass-through current transformer. The primary function of the current transformer is to reduce the current value to be measured to a value that is acceptable to the measuring devices (generally 1 to 5 A).
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