3 pole or 4 pole isolator?

[wozzit99]

Hi

When installing a 3 phase distribution circuit what determines the type isolator to use ( 3 or 4 pole ). In other words does the neutral have to be switched?


Cheers

 

[malcolmsanford]

Depending on type of installation and earthing system

 

[wozzit99]

Hi malcomsanford

The earthing system is a TT. As a matter of interest what isolators would i use for other earthing systems tncs, tns?
The installation is a distribution circuit 3 phase feeding a 2 way 3 phase dis board.

Cheers

 

[malcolmsanford]

If it is a TT supply then you will need to fit a 4 pole breaker as per reg 537.1.2

A lot of industrial/commercial equipment, especially rotating machines use regenerative breaking which requires the neutral not be isolated/switch

 

[wozzit99]

Just a thought what about if the service is tncs but you cant export the earth to another building so making that part of the system TT

Can you still use a 3 pole isolator at the service end?

 

[rich.250]

Yes because that is tncs. Also why can't you export tncs?