Grounding and probe

[cropwell]

Some people think that single phase AC Neutral is synonymous with Ground (Earth). It is not! It is phase neutral for the live, which is one of the three phases used for domestic supply. Different houses in the same street can be supplied from different phases. That, however, is a digression. There is often a voltage difference between Neutral and a local earth. That voltage will depend on several factors. At my house it is 10v. Power supplies can be double insulated, but the output Ground should be connected to Earth, as should the whole machine. In some countries, the Earth terminal on the Mains socket can not be relied on to give protection from shock hazards and so a ground rod is desirable.

[Clive S]

Some people think that single phase AC Neutral is synonymous with Ground (Earth). It is not! It is phase neutral for the live, which is one of the three phases used for domestic supply. Different houses in the same street can be supplied from different phases. That, however, is a digression. There is often a voltage difference between Neutral and a local earth. That voltage will depend on several factors. At my house it is 10v. Power supplies can be double insulated, but the output Ground should be connected to Earth, as should the whole machine. In some countries, the Earth terminal on the Mains socket can not be relied on to give protection from shock hazards and so a ground rod is desirable.

Yes Rob but generally in the UK in towns not necessary in the country The neutral in generally connect to the earth at the consumer unit. Just saying

[cropwell]

Yes Rob but generally in the UK in towns not necessary in the country The neutral in generally connect to the earth at the consumer unit. Just saying

In my house (in the country), the neutral is definitely not connected to Earth as if I short N to E it will trip the RCCB, by causing a Live-Neutral current imbalance of > 30mA. The wiring was brought up to regs about 5 years ago with a new consumer unit.

The OP lives in Buenos Aires* and I do not know the regs in Argentina or the state of his workshop wiring.

*If his flag header info is correct.

Rob-T (just to avoid confusion)

[john swift]

For one of the supply wires to be "Neutral" it has to be connected to earth / ground other wise it would be just another line

the earth connection has to be a low enough impedance to ensure the fuse or circuit breaker opens fast enough to remove the danger when you have live to neutral or live to earth fault

Here in the UK
Depending on the wiring system used in towns and cities the utility company may supply the earth and neutral as separate earth and neutral conductors (TN-S system)
or as a combined earth & neutral (TN-C system) some times with multiple earths along its length

For rural supplies the you may have to supply your own earth (TT system)
even though the utility will have connected the neutral to earth at the transformer

It does not matter if the neutral / earth connection is 3 miles down the road at the supply transformer or the utility junction block next to your Kw/Hr meter

what matters is the neutral is earthed before it passes through the residual current circuit breaker ( RCCB)
what you see when measuring the difference between Earth and Neutral is the volt drop along the neutral wire when the 3 phase supply cable has an unbalanced load

when ever the neutral wire out of the RCCB is connected to the earth there is an imbalance between the live and neutral currents which trips the breaker - (you have an earth path in parallel with the neutral reducing the neutral current the RCCB sees)
usually the circuit breaker is designed to trip at 30mA
( depending on the application various trip currents are available )

In my part of South Lancashire my mains supply varies between 243V and 248V
depending on the time of day - just now its 245V

John

[cropwell]

If Neutral is connected to Earth, there should be no current flowing to cause a Live-Neutral imbalance. However, when I accidentally shorted a light fitting neutral to earth With the light switched off, the whole house was sent into darkness. I have a very good local earth strapped to a copper water feed pipe. This leads me to assume that, although the phase neutral may be earthed at the substation, there is enough of an induced voltage in the supply line on its' journey to my house to cause a RCCB trip if earth is connected to neutral.

My point is that, UK has regulations in place to try to ensure electrical safety and recently built or rewired houses should be relatively OK, but older premises and different supply and use regs in other countries may pose a greater risk.

Rob-T

[john swift]

the devil is going to be in the detail

when my home was rewired a single RCCB was fitted to protect all circuits
(these days a split consumer unit would be fitted with 2 RCCB's)

so if I shorted a light fitting like you then the RCCB will trip depending on
1) which earthing system has been used
2) the total load taken by mains powered devices in the house

with a TN-C system with the earth & neutral combined
the imbalance the RCCB detects depends on the total load in the house

with a TN-S system the imbalance the RCCB detects will be a combination of the total load in the house and the volt drop along the neutral in the 3 phase cable buried under the road

John

[Clive S]

Then there are the mcb and rcd combined in one unit called a RCBO