• The disconnection of a fixed neutral conductor on TN C S and TN C system is unnecessary and could introduce more significant levels of risk and harm.

• Disconnection and temporary opening of a Fixed neutral link can result in a situation where the link is not replaced, which can lead to serious con. sequences.

Always prove dead before commencing working 

Phase to phases

Phase to neutral 

Neutral to Earth 

• In situations where neutrals are shared the disconnection of the link/conductor can lead to significant voltage instability on dependant connected circuits. in TN-C-S and TN-C. 

Provided that, where the N and PE have been split in a TN-C-S system, the neutral should not be earthed again beyond the "split".

Agreed, but I suspect Mike was thinking of those parts of the world where it's conventional to keep the system TN-C well into the consumer's installation (often to the final distribution board) - often tagged Multiply Earthed Neutral (MEN) . We'd probably refer to it as a CNE or PEN conductor rather than just N, but the convention isn't universal.

    - Andy.

If you look at G99 document there are many instances of neutral being bolted. This is also the case in BS7430. Note both documents are “EU” harmonised.

 Please also remember that a downstream UPS relies on the earth/neutral reference.

Russ

I refer melord to G99…. where there even delta wound generators that depend on the supply neutral and protection systems….

Russ

Consider this sort of thing - total shocker in the UK, normal practice for OZ/NZ . AS3000 claiims descent from 60364  much as BS7671 does, Makes RCD cover for sub mains impossible but simple concentric cable gives flash-bang ADS against pick-axe strike, much like UK DNO/BNO wiring. So long as polarity is never wrong of course.

In other news I'm off to South America soon - I'll try and take some pics for the 'common practices not allowed here' album.  Mike

mapj1 said:

Consider this sort of thing - total shocker in the UK, normal practice for OZ/NZ . AS3000 claiims descent from 60364  much as BS7671 does,

Yes, TN-C is permitted in the installation in IEC 60364. It's (generally) prohibited by ESQCR in the UK.

Perhaps worth looking at safety incidents in Australia (but I understand not yet experienced in New Zealand) ?

Russell Bulley said:

 Please also remember that a downstream UPS relies on the earth/neutral reference.

I'm not with that 100 % ... yes, it's a consideration but a transformer can be provided before, or as part of, the UPS. The big issue for the designer is to address how the neutral upstream of the UPS is to be maintained when the "more essential" or perhaps "critical" loads of the UPS are being powered?

Remember that the UPS standard itself acknowledges this issue, and sadly it's often left to the installer to sort all this out.

Maybe I'm missing something, but isn't that just wiring an outbuilding TT?  I thought that was commonly done in the UK.

I missed the earth neutral link in Mikes sketch as well and for a brief moment thought that he had already started into the South American reds!

It s not my sketch, its lifted from a 'how to do supplies to farm out buildings'  from an equivalent of wiring matters magazine  for Australian Electricians. 

It is just so far in many ways  from accepted UK practice as to be really interesting. (and they consider TT to be the work of the dark side... although NZ have been consulting if they should start to consider it.  link)

Mike.

PS yes, look for the NE links in the panel/ CU for each building.

Mike.

I'm more of a beer man myself ...

M.

I'm more of a beer man myself ...

M.