Isolation of the neutral conductor: Difference between revisions
From Electrical Installation Guide
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|A= 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 | |A= 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 | ||
|B= The neutral overcurrent protection is not necessary: | |B= The neutral overcurrent protection is not necessary:<br> | ||
- If the neutral conductor is protected against short-circuits by a device placed upstream, or,<br> | |||
- If the circuit is protected by a RCD which sensitivity is less than 15% of the neutral admissible current. | |||
|C= In some coutries the rules applied for TN-S are the same as the rules for TN-C }} | |C= In some coutries the rules applied for TN-S are the same as the rules for TN-C }} | ||
Latest revision as of 09:48, 22 June 2022
(see Fig. G68)
It is considered to be the good practice that every circuit be provided with the means for its isolation.
Fig. G68 – The various situations in which the neutral conductor may appear
| TT | TN-C | TN-S | IT | |
|---|---|---|---|---|
| Single-phase
(Phase-Neutral) |
or |
|
|
 [a]
or |
| Single-phase
(Phase-Phase) |
 [b]
or |
|
[b]
or |
|
| Three-phase four wires
Sn ≥ Sph |
|
|
[c]
|
 [a]
or |
| Three-phase four wires Sn < Sph |
|
|
[a]
or |
- ^ 1 2 3 The neutral overcurrent protection is not necessary:
- 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. - ^ 1 2 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
