Switched Neutrals or not

[StephenRowley]

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This question is purely out of interest, I'm a substation apprentice while we do some LV installation work its not much and no design work fitting only.

But today I've been helping a sparkie friend do some work(just attaching conduit to wall no actually wiring) for local community group.

So the question why is the neutral to the DB from a switched fuse isolated (if that the right term) not switched but at the DB it's self does switch neutrals?

 

[haptism]

Most switch fuses are double pole, meaning they switch line and neutral

 

[davesparks]

Generally neither a switch fuse nor a DB will have switching of the neutral in a TP installation unless it is is a non TN system or a special type of installation.

Most TP DBs will have a triple pole main switch with a test/disconnect link for the neutral which requires the use of a tool.

 

[StephenRowley]

Could be I'm mistaken, I'm a substation apprentice so not my area of expertise.

Would there be anything wrong with having the neutral switched, should also mention it's 3 phase board?

 

[Deleted account]

Could be I'm mistaken, I'm a substation apprentice so not my area of expertise.

Would there be anything wrong with having the neutral switched, should also mention it's 3 phase board?

Nothing wrong there as long as the nutral was switched along side the line in I.e. Double pole switch.
However isolating the neutral independant of the live a no no.

 

[davesparks]

Would there be anything wrong with having the neutral switched, should also mention it's 3 phase board?

If the neutral is to be switched then it should ideally be by a last break/first make contact to prevent the lives being connected before the neutral.
If the neutral contact of the switch were to fail for any reason you could end up with the installation having a floating neutral which can be dangerous.

In an installation where the neutral is reliably connected to earth (TN system) there is no need to isolate the neutral and so the risk of a failed switch contact can be avoided by nit switching the neutral.

In other installations where the neutral can have a voltage between it and earth it needs to be isolated to achy eve a proper isolation and so it must be switched.