Sizing Electrical Installations: The Main Criteria to Study

Sizing an electrical installation is a complex art insofar as it requires considering strategic, economic, technical, and contractual imperatives. In addition to these, normative and regulatory criteria must also be taken into account. This article tells you more and presents the sizing methodology.

The Main Criteria to Study When Sizing Electrical Installations

There are two types of texts governing the criteria to be considered for the sizing of electrical installations. These are the normative texts and the regulatory texts.

Regulatory texts

They define the general framework for implementing electrical installations and the goals to be reached. In particular, we note the protection of workers, the protection against the risks of fire and panic in establishments open to the public (ERP), the protection in buildings for residential use, and the protection in high-rise buildings (IGH). Their application is mandatory.

We also note the technical conditions to be met by electrical energy distributors, the safety of people, animals, and property, or equipment compliance with electromagnetic compatibility criteria.

The Normative Texts

The normative texts represent the expression of the rules of the art. They also define the means to achieve the goals set by the regulations. Therefore, the application of these texts is strongly recommended and can sometimes even be made compulsory by a decree.

The Sizing Process of an Electrical Installation

Once all the preliminary studies have been carried out (power balance, source power, schematic diagram, etc.), the sizing of an electrical installation can be done according to the following methodology.

Network data: calculate the power of the short-circuit current at the origin of the circuit. In other words, define the power to be carried;

choice of protection devices: determine the operating currents for each outlet;

conductor cross-section: calculate the cable cross-sections, checking the correct choice of protection devices, the maximum protected length, and the thermal stress;

control: check the voltage drop, complete the protection devices against indirect contacts;
Confirmation: confirm the cable sections and their correct protection;

installation: IP choice of enclosures and installation.

It should be noted that all these steps can be performed manually, using the UTE C15-105 guide, or by computer, using the DOC calculation and design software.

Protection Against Electric Discharges

The human body is very sensitive to electric current. That is why there are measures to protect people and animals against electric shocks.

Protection Against Direct Shocks

In addition to the traditional protective measures (distance, obstacles, insulation), there are additional protective measures such as using residual differential devices. The rated differential current must be less than or equal to 30 mA in this case.

Protection Against Indirect Shocks

Following a fault between an active part and an earthed mass, for example, a protection device must automatically separate the faulty circuit or appliance from the power supply so that a voltage higher than 50 volts AC cannot be maintained for a sufficient time to create a risk of physiopathological effect.

In addition, it is recommended to implement the conventional method to facilitate the application of the protection rules. This method makes it possible to determine the breaking times not according to the presumed contact voltage but according to the nominal voltage of the installation.

In short, the sizing of electrical installations is based on two main criteria: regulatory texts and normative texts. Their application is guaranteed by a set of rules and prescriptions defined by the standardization organizations.

Sizing Electrical Installations: The Main Criteria to Study

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