Neutral - Earth Link in Main Switchboard

In the UK we never "re-earth" a true N

That is certainly the official position,and should be the situation all the time. Although we do sometimes come very close to it with some generator switching and building sized UPS arrangements where there may be multiple N-E links as part of the local distribution networks,and to make sure that ADS works when runing on UPS. Data centres with dual 11kV transformers that can be switched to be paralelled or split and have an N-E link each can become particularly confusing.

  However  as the wiring between the links is rated for load current, arguably that is electrcially more like having redundant PENs. It does mean great care should be taken if it ever seems that an NE bond needs to be removed for any reason.


I have also had the fun (as a one off special), of wiring the CPC of an American made UPS back though the current transformer of the earth fault relay, so it's case could be earthed, but  the internal NE-short it created  did not look like a fault, to make it work, the CPC of the final circuits did not go via the UPS or pass through the core, so the final circuits still had earth fault protection when the UPS was not operating.  Given the whole thing was running from a priveate genset, there was no real issue.

Very much not  BS7671 compliant, but it is not actually an offence to link a CPC and a neutral, so long as the same length wire is not used for both functions for any non-distribution wiring. (The UK LAW is A consumer shall not combine the neutral and protective functions in a single conductor in his consumer’s installation )

Does not quite say you cannot have two conductors and link them in more than one place, though BS7671 does not like that.

 

In the UK we never "re-earth" a true N

That is certainly the official position,and should be the situation all the time. Although we do sometimes come very close to it with some generator switching and building sized UPS arrangements where there may be multiple N-E links as part of the local distribution networks,and to make sure that ADS works when runing on UPS. Data centres with dual 11kV transformers that can be switched to be paralelled or split and have an N-E link each can become particularly confusing.

  However  as the wiring between the links is rated for load current, arguably that is electrcially more like having redundant PENs. It does mean great care should be taken if it ever seems that an NE bond needs to be removed for any reason.


I have also had the fun (as a one off special), of wiring the CPC of an American made UPS back though the current transformer of the earth fault relay, so it's case could be earthed, but  the internal NE-short it created  did not look like a fault, to make it work, the CPC of the final circuits did not go via the UPS or pass through the core, so the final circuits still had earth fault protection when the UPS was not operating.  Given the whole thing was running from a priveate genset, there was no real issue.

Very much not  BS7671 compliant, but it is not actually an offence to link a CPC and a neutral, so long as the same length wire is not used for both functions for any non-distribution wiring. (The UK LAW is A consumer shall not combine the neutral and protective functions in a single conductor in his consumer’s installation )

Does not quite say you cannot have two conductors and link them in more than one place, though BS7671 does not like that.