Isolation of the neutral conductor: Difference between revisions
From Electrical Installation Guide
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Revision as of 17:17, 16 May 2017
(see Fig. G64)
It is considered to be the good practice that every circuit be provided with the means for its isolation.
| TT | TN-C | TN-S | IT | |
|---|---|---|---|---|
| Single-phase
(Phase-Neutral) |
or |
|
|
 [b]
or |
| Single-phase
(Phase-Phase) |
 [a]
or |
|
[a]
or |
|
| Three-phase four wires
Sn ≥ Sph |
|
|
[c]
|
 [b]
or |
| Three-phase four wires Sn < Sph |
|
|
[b]
or |
[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:
- 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.
[c] In some coutries the rules applied for TN-S are the same than the rules for TN-C
Fig. G64 – The various situations in which the neutral conductor may appear
