Isolation of the neutral conductor
(see Fig. G68)
It is considered to be the good practice that every circuit be provided with the means for its isolation.
|Three-phase four wires
Sn ≥ Sph
|Three-phase four wires Sn < Sph||[a]|
- - If the neutral conductor is protected against short-circuits by a device placed upstream, or,
- - If the circuit is protected by a RCD which sensitivity is less than 15% of the neutral admissible current.
- The neutral overcurrent protection is not necessary:
- Authorized for TT or TN-S systems if a RCD is installed at the origin of the circuit or upstream of it, and if no artificial neutral is distributed downstream of its location
- In some coutries the rules applied for TN-S are the same as the rules for TN-C