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Neutral Power System

The standard NF C15.100 of May 1991 recommends and describes the principles governing the construction of low frequency electrical installations in France. This standard recognises three ways of constructing neutral point connections:

• IT, referred to as "impedent neutral "
• TT, referred to as "earth-neutral " conductor
• TN, referred to as "connecting to neutral"

These are not standardized names.

Note: For TN neutral point connections, there are three construction principles:

• TN-C
• TN-C-S
• TN-S

The method of protecting persons and hardware depends on the neutral point connection constructed. In the case of an electrical installation which uses a TT neutral point connection, the use of circuit breakers equipped with a differential (Residual Current Protective Device) is MANDATORY.

Note: The neutral point connection can only be changed from a power supply interface, so as to ensure galvanic isolation.

Constructing a TN

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