Revision Question

[cfcsi]

Just going through a few revision questions and this one popped up:

Q: An isolator in a 3 phase four wire system must disconnect

1. The 3 phase and neutral
2. The 3 phase only
3. The 3 phases , nuetral and earth
4. The neutral only

They give the answer as 2.

I would have said 1. -
Can someone explain the given answer???

Cheers

 

[Notsosmart]

The clue is in the question; an isolator in a 3 phase 4 wire system.
It doesn't state where this isloator is or what it is controlling, the cable could therefore be the supply to a TN-C(-S) system.

If you look in section 537; specifically 537.1.2 "PEN conductors shall not be isolated or switched"

 

[cfcsi]

Dont have BRB to hand but will look that up when home.

cheers

 

[Roger]

Hi there,

Read it today in the OSG page 33.

'for a 3 phase supply to an installation forming part of a TT system,an isolator must interrupt the line and neutral conductors.In an TN-S or TN-C-S system only the line conductors need to be interrupted'

Cheers