Isolation of the neutral conductor: Difference between revisions
From Electrical Installation Guide
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{{Menu_Sizing_and_protection_of_conductors}} | {{Menu_Sizing_and_protection_of_conductors}} | ||
[[File:DB422336.png]] | |||
(see {{FigRef|G68}}) | |||
It is considered to be the good practice that every circuit be provided with the means for its isolation. | |||
{{tb-start|id=Tab1222|num=G68|title=The various situations in which the neutral conductor may appear|cols=5}} | |||
{| class="wikitable" | |||
{| | |||
|- | |- | ||
! | |||
! TT | |||
! TN-C | |||
! TN-S | |||
! IT | |||
|- | |- | ||
| Single-phase | |||
| [[ | (Phase-Neutral) | ||
| [[ | | [[File:DB422337.png]] | ||
| [[ | '''or''' <br> | ||
| [[ | [[File:DB422340.png]] | ||
| [[File:DB422338.png]] | |||
| [[File:DB422337.png]] | |||
| [[File:DB422339.png]]{{tn|B}} | |||
'''or''' <br> | |||
[[File:DB422337.png]] | |||
|- | |- | ||
| Single-phase | |||
| [[ | (Phase-Phase) | ||
| [[ | | [[File:DB422344.png]]{{tn|A}} | ||
| [[ | '''or''' <br> | ||
| [[ | [[File:DB422345.png]] | ||
| [[File:DB422345.png]] | |||
| [[File:DB422344.png]]{{tn|A}} | |||
'''or''' <br> | |||
[[File:DB422345.png]] | |||
| [[File:DB422345.png]] | |||
|- | |- | ||
| Three-phase four wires | |||
| [[ | Sn ≥ Sph | ||
| [[ | | [[File:DB422341.png]] | ||
| [[ | | [[File:DB422342.png]] | ||
| [[ | | [[File:DB422341.png]]{{tn|C}} | ||
| [[File:DB422343.png]]{{tn|B}} | |||
'''or''' <br> | |||
[[File:DB422341.png]] | |||
|- | |- | ||
| Three-phase four wires Sn < Sph | |||
| [[ | | [[File:DB422343.png]] | ||
| | | | ||
| [[ | | [[File:DB422343.png]] | ||
| [[ | | [[File:DB422343.png]]{{tn|B}} | ||
'''or'''<br> | |||
[[File:DB422341.png]] | |||
|} | |} | ||
{{tb-notes | |||
|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:<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 }} | |||
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
