Earthing on the neutral

[Tangy]

What is an isolated neutral system?

Is this the same as an unearthed system ?
How does it differ from direct earthing and impedance earthing?

 

[rbulsara]

It is not a common term. Where did you hear that?
Isolated ground is a more familiar term.

Rafiq Bulsara

http://www.srengineersct.com

 

[tem1234]

The neutral is isolated from the ground.

see pic attached.

I'have never seen this exept in book.

 

[ScottyUK]

Occasionally I find something positive to say about Groupe Schneider and this is one of them: the 'Cahier Techniques' set of technical documents is an excellent reference, certainly for anyone in Europe or within the European sphere of influence, and many of them will have global appeal.

ECT 172 probably answers your specific question about IT systems plus a load of related ones you haven't thought of yet, and the whole document set is available here.


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If we learn from our mistakes I'm getting a great education!

 

[Kiribanda]

Tangy,
As far as I can remember, IT (per IEC 60364) system of earthing is still being used in Norway for 400 V domestic network and the earth leakage protection was provided by overcurrent protection at the early stages.As there were lot of house fires due to this grounding method,subsequently Residual Current Circuit Breakers (RCCB)were introduced for earth leakage protection in domestic installations.

Anybody from Norwegien power system experience please correct me.

 

[m3ntosan]

Tangy,

"isolated neutral system" & "unearthed system" I guess you're talking about distribution networks with no link between neutral and ground.

Usually you can operate with neutral isolated from the ground if the capacitive currents are lower than 10 Amps and with neutral "compensated" with Petersen coil or "treated" with resistance for capacitive currents higher than 10 Amps.

Like I told you in another thread, there's no earth fault (short-circuit)for single phase touching the ground in isolated neutral from ground operation. Due to low current magnitude and increase of voltage from phase-ground to phase-phase on the healthy remaining phases,you can decide to continue operation for a limited amount of time, that's the advantage. The disadvantage is that you may end up with broken isolation or affecting the long time health of the isolation.