Earth and Neutral Query

[baconhead]

I have just noticed when I was changing a light fitting in my kitchen that the earth cable seems to be capable of working as a neutral. This was discovered by accident. I later checked using a circuit testing device and there appears to be a circuit between earth and neutral. Is this supposed to happen? If not, what is the easiest way to check where the fault is. The house was rewired by a professional Electrician about 9 years ago and there has been no alterations since.

 

[PrenticeBoyofDerry]

It's likely that your earth is connected to the neutral via the supply, that's why your are getting a continuity reading.

 

[dannyboi2003]

You probably have a PME supply to your house where the Earth and Neatral share a common conductor on the DNO side, on your side of the wiring everything stays separate. As PBD has already said its nothing to worry about but do make sure you use the neutral on your fitting and not the earth

 

[Spark123]

You get similar results with TN-S too. The earth (protective conductor) is connected to neutral back at the suppliers transformer.
You must not use the protective conductor as a neutral tho - if the protective conductor was to break somewhere inside your house you will end up livening up all connected metalwork anything downstream of the break.
The protective conductor is also usually smaller than the live/neutral in a twin and earth. Think it is only 1mm² where they are the same.

 

[ban-all-sheds]

I have just noticed when I was changing a light fitting in my kitchen that the earth cable seems to be capable of working as a neutral. This was discovered by accident.

My curiosity is piqued...

 

[baconhead]

Thanks for your responses this has been very helpful. Is there anyway I can check to confirm what type supply I have or is this just the norm these days?

 

[Steve]

The service fuse should have a sticker on or around it, stating that its PME. IF ITS PME of course.

Alternatively there are diagrams of the various types of earth on this forum and in the wiki.

 

[RF Lighting]

Or post a photo on here, and someone will be able to identify it for you.

 

[Paul_C]

You are going to read continuity of some sort between neutral & earth on all installations fed from the public supply.

If it's TN-C-S (PME), the two are bonded at the cutout ahead of the meter, so you'll be reading just the resistance of the conductors within the house.

If it's TN-S the neutral is bonded to earth at the supply transformer, so you'll read the resistance of your conductors plus the supply conductors.

And if it's TT, the neutral is still earthed at the transformer, so you'll read the resistance back to that point via your own ground rod and the earth, although in this case the reading will be considerably higher - typically anything from a few ohms to a few hundred ohms.

 

[kai]

Another point, when doing a continuity test between earth and neutral, you are very likely to trip out the main RCD, when doing the test, as the test current will pass through your neutral conductor, back to either the star point (TNS) , or the service fuse block (PME), and back up the earth core. as the live is bypassed the RCD trips out.

 

[sparkyspike]

when doing a continuity test between earth and neutral, you are very likely to trip out the main RCD

So you test continuity between neutral and earth with the power still on, do you?

To get a reading between N + E, disconnect the double pole isolator first.