18TH Regs Chapter 46 - 46.2

[John-]

Hi

This reg states that TNCS or TNS systems do not need the neutral isolated. Is that at sauce or generally?
Why?
What about TT systems?

Thanks

John

 

[Ian1981]

In a TN system the neutral is considered to be at or relatively close to 0 volts /earth potential as the earthing conductor returns to the source and is connected at the star point where the neutral is also connected making them the same potential.
A TT system has no earthing conductor returning to the source , the earth fault loop impedance is via the general mass of earth through an earth electrode (s) so a difference in potential can exist.
In a 3 phase and neutral TT installation the installation must isolate all live conductors by a 4 pole isolator at the origin
In a TN 3 phase and neutral installation only the line conductors require isolating at the origin
In a domestic installation regardless of earthing arrangement type, a double pole switch must isolate the installation at the origin.
Part 7 electrical installations may also require the neutral is isolated in certain different earthing arrangements

 

[buzzlightyear]

I could not put it better me self ,when any post goes up I wish they put a page to it on the regs .

 

[John-]

Thanks Ian. The reference to domestic you make is that 462.1.201 (p121)? Is that because of the assumption that non-domestics are three phase or more to do with functional switching or none of the above? Thanks.

 

[buzzlightyear]

The reference to domestic you make is that 462.1.201

that it means of isolation . whether a fuse or isolator .

 

[Ian1981]

Thanks Ian. The reference to domestic you make is that 462.1.201 (p121)? Is that because of the assumption that non-domestics are three phase or more to do with functional switching or none of the above? Thanks.

Because domestic installations are used by ordinary persons who are prone to careless actions with regards to electricity

 

[John-]

Tanks Ian. Still uncertain on a few things but going into the area of being a pedant so will stop - cheers.

 

[Ian1981]

Tanks Ian. Still uncertain on a few things but going into the area of being a pedant so will stop - cheers.

Glad I could help John