tp+n sub main isolation

[eggandspoon]

Hi all

was looking at a 3 phase and neutral sub main 10mm swa to garage ramp - already installed.

the supply was via a butchered wylex metal 8 way single phase consumer unit with a merlin 3 phase isolator supplied by 25mm tails and linked to a merlin 50a tp b mcb using 16mm tails .

the neutral in is into the neutral bar as is the neutral out.

apart from this being a bit rough- does the isolator for this ( or any TP&N install) need to be TP&N or is TP acceptable?

Thanks

 

[holmslaw]

..

 

[1john]

Sometimes these isolators have a neutral link which can be disconnected once the phase/line conductors have been isolated.

 

[eggandspoon]

thanks for the replies

why in single phase is it normal to have a DP isolator yet it is acceptable to have only the Line isolated in 3ph !?

therefore would an mcb on the phase or a single pole isolator(if you can get one) be acceptable as an isolator on a single phase sub main

also you can buy TP isolators and TP&N isolators what is the function of isolating the neutral if this is not required

just wondering...................

thanks

 

[Risteard]

One reason would be for TT systems which require all live conductors to be broken.

If ordinary persons will be working on it then you also may wish to break all live conductors, but I take it that this is a commercial scenario so that would be unlikely.

 

[deafboy]

Its also something to do with 3 phase unbalanced loads where if the nuetral where to be disconnected even slightly prior to one of the phases things could go seriously wrong

same reason most 3 phase boards also have a solid neutral connector

its generally frowned upon to isolate the nuetral in tpn unless you can ensure the nuetral dissconnects last

 

[eggandspoon]

mmm thanks for the replies.

the definitive is due to unbalanced TP loads and N isolating first ?

and in single phase isolating all lives due to non pro users using system ?

FYI this supplies a 4 post ramp in a domestic car enthusiasts garage.