240 between Neutral and earth but 0v between Line & Neutral

[EagerApprentice]

Greeting Learned folk
Why would you get 240v from Neutral to earth and 0v Line to Neutral? I'm getting 240 v Line to Earth.
I have around 4 fluorescent luminaires lights not working and am looking for ideas before I start fault finding.
Any help or suggestions would be greatly appreciated!

 

[Darkwood]

Hi guys Eager is a Trainee at the moment so please respect his learning curve and be gentle... I am letting this into the main forum for the moment while we sort a few things out cheers ...Darkwood!

 

[Plonker 3]

Think about what potential the neutral should be at. Then think why maybe the neutral isnt at that potential.

Measuring the voltage between L-N and that should help you too.

 

[EagerApprentice]

There was 0v between line and neutral.

 

[Plonker 3]

So what does that tell you about the continuity of the conductors?

 

[EagerApprentice]

I thought there was a break in the neutrals somewhere, so why would there be voltage between neutral and earth?

 

[Darkwood]

If the voltage between L and E is 230v and respectively the voltage between N and E is also 230v (1ph system) then this suggest that the N is at the same potential as the L so measuring L-N will show 0v or their about.

This floating voltage on the N may be because your return to the distribution N is not connected or lost somewhere - that would be the first area to look into (broken N)

 

[EagerApprentice]

Thank you Darkwood. You made that really clear. Also thanks Dillb for responding.

 

[Richard Burns]

Remember the value you see is the potential difference between the two cables.
Because the supply voltage is 240 V (230 V) if you get this value then one of the points is at full voltage and one is at zero voltage.


The Neutral to earth is 240 V.
Therefore either the neutral or the earth is at 240 V and the earth or the neutral is at 0 V.

You have 0 V line to neutral.
This may seem that they are both at 0 V but actually it means they are both at the same voltage and there is no difference between them.

You get 240 V line to earth.
Therefore either the line or the earth is at 240 V and the earth or the line is at 0 V.

From this since earth is normally zero volts and line is normally 240 V, you can now assume that:
Earth is at zero volts
Line is at 240 V
Neutral is at 240 V

Normally Neutral is at approximately zero volts as it is earth referenced on the supply side, because the neutral is not a zero volts it is not connected to the earth reference, i.e. the neutral is disconnected from the consumer unit.
Because the neutral is at 240 V the neutral is connected to the equipment and is being raised to 240 V by the line potential via the equipment, but the equipment does not drop voltage as there is no current flow because the neutral is disconnected.

 

[EagerApprentice]

Remember the value you see is the potential difference between the two cables.
Because the supply voltage is 240 V (230 V) if you get this value then one of the points is at full voltage and one is at zero voltage.


The Neutral to earth is 240 V.
Therefore either the neutral or the earth is at 240 V and the earth or the neutral is at 0 V.

You have 0 V line to neutral.
This may seem that they are both at 0 V but actually it means they are both at the same voltage and there is no difference between them.

You get 240 V line to earth.
Therefore either the line or the earth is at 240 V and the earth or the line is at 0 V.

From this since earth is normally zero volts and line is normally 240 V, you can now assume that:
Earth is at zero volts
Line is at 240 V
Neutral is at 240 V

Normally Neutral is at approximately zero volts as it is earth referenced on the supply side, because the neutral is not a zero volts it is not connected to the earth reference, i.e. the neutral is disconnected from the consumer unit.
Because the neutral is at 240 V the neutral is connected to the equipment and is being raised to 240 V by the line potential via the equipment, but the equipment does not drop voltage as there is no current flow because the neutral is disconnected.

i think we have a winner here folks. Many thanks.