• 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. 

• 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. 

The disconnection of a fixed neutral conductor on TN C S and TN C system is unnecessary

Perhaps not always true - say you had local generation as a switched alternative to the grid - the change-over switch would need to switch (and isolate) N to comply with 444.4.7. (Wouldn't be needed in a pure TN-C system of course but the ESQCR prohibits PEN conductors in consumer's installations.)

That then begs the question, as far as the downstream installation is concerned, how reliable is the N connection with Earth? Moving contacts are generally less reliable than solid joints, and not all disconnection devices guarantee not to close the L contacts if the N has failed to close, or prevent the N from opening if the L contacts have welded closed. If you consider that the N downstream of the change-over switch isn't reliably held at close to Earth potential, can you justify working on such a conductor without isolation?

   - Andy.

Hi Andy, 

You are right about the generator connection to the system you shall use a 4-pole change-over switch. 

My comment was mostly above the question about the confusion of neutral isolation. With three poles or single pole switch.

Many thanks 

Arya

Note that in countries that use BS7671 but do not have an equivalent to that rule in the ESQCR, your decision may not be the same, and in countries like Ireland , where the underpinning regulations are the same as those that drive '7671, but the national variant is not, then you may well be permitted to permanently connect neutrals to earth consumer side anyway so long as it is safe to do so.

Mike.

Mike. 

If you are in a country using TT or IT systems, then you will install two poles or four poles circuit break or switch to ensure during the isolation, the neutral is disconnected. However, it isn't required in TN-C or TN-C—S system because the neutral is already connected to the earth at the source 

Arya

because the neutral is already connected to the earth at the source 

But isn't N is solidly connected to Earth (i.e. the general mass of the Earth, as defined) at the source for a TT system too?

   - Andy.

mapj1 said:

then you may well be permitted to permanently connect neutrals to earth consumer side anyway so long as it is safe to do so

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". There are a number of reasons for this, including unpredictable operation of residual current devices in the "-S" portion of the TN-C-S system.

Similarly, there should only be one neutral earthing ("system referencing") connection in a TT or TN-S system.

This is the same in all countries harmonized with HD 60364-4-44 or IEC 60364-4-44 (as well as other parts of HD / IEC 60364).

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