Neutral switch question

oldtimer · Sep 26, 2010

Think of it this way earth and neutral are both 0v potential but the earth is a protective circuit the neutral is the return path for the load both may be the same as you say but both do different jobs if you want to think of it that way.
Things do get a bit fuzzy in the modern house with plastic baths, sinks,pipes but rememember 50years ago + most installations got their main earth from the gas and or water supply pipe because they were metal so in a house then the pipework for the water and heating were all metal ie storage tank in the attic was tin so your installation was mechanically and electrically sound then they started putting in pastic tanks /sinks hence why the cross bonding. Now fast forward we have RCD protection and we no longer get our earth from water gas we no have to bond them as they enter the house

Des 56 · Sep 26, 2010

A suppliers 3 phase transformer, secondary side, will have the ends of each of the 3 phases connected together,this is the star point
At that common point the phases are balanced,they each use the others for current flow,so at any given moment ,if you add up + current flow and _ current flow it will always be 0 at the common point,irrespective of the direction of that flow in the individual phase

Potential difference is what it says, a difference of potential, between one part of a possible circuit, and another part of a possible circuit

Between the outgoing points of each phase,there is 415 volt potential difference,because if you look at the circuit,there are 2 windings in series
Between any one of those phases and the common (or neutral) point,there is just the one winding which is 230 volt potential difference between that phase and the common point

The possible circuits are through the transformer secondary windings only at this time

If a connection is made from the common or neutral point of the transformer and with earth,"no current will" flow,there is no possible circuit,so no potential difference can exist,
The neutral or common point is now connected via an electrode to the ground

Taking one of the phase connections and a connection off that common/neutral point to a house will give a potential difference in that house of 230 volt between the phase and the common or neutral ponit

Practically speaking,when the circuits in the house are open,there will be no potential difference between the neutral and earth, because they will be connected at the star point at the suppliers transformer, so no potential difference exists

Once you get your head around the supply arrangements you will notice

Earth fault currents can get back to the transformer more easily via the neutral conductor of a TNC-s than it could via an earth rod,which uses the ground,that is called a TT earthing system Terra to Terra
In that TT system it means fault current has to travel down the rod through the earth and up the spike at the suppliers end, to the common connection(star point neutral), through the winding, and back again to the property ,

The difference between a Tnc-s supply and a TT supply, is that, earth fault currents can get back easier with a Tnc-s or TNs than a TT because the return is via a conductor ( sheath of an SWA or the neutral conductor) rather than via terra firma which does not conduct easily