Live earth

[peter_226]

I moved house about six months ago and have just noticed that
there is a problem with the electricity. Using a volt meter on the mains ring I get the following readings:-

Live/neutral = 240 Live/earth = 130 Neutral/earth = 80

I was told the house was rewired about 10 years ago and the fuse box was fitted about two years ago and has an 80a RCD. I have had no problems with tripping fuses etc. No recent work has been done to my house so I preume it is not a nail through a wire. Can an appliance cause this?

What do I have to do to find this fault and in what sequence?

Thanks

 

[JohnD]

Can you lay your hands on a digital camera and put up a photo of the area around the meter and consumer unit, especially showing the cable head and the wires coming out of it, and where they go? I am particularly intertested to know if it has a large green-and-yellow earth wire coming off the side and going to the consumer unit.

In the meantime, start asking round your friends and neighbours for recommended qualified local electricians... you may be needing one.

P.S. it will not be solely due to an appliance, I think your installation has a design or installation defect. Do you live in town or country, do you have an overhead or underground supply, have you an opinion on how professional and neat the rewire was?

 

[Adam_151]

Sounds like the earth is floating, rather than connected to earth

confirm continuity between earth bar and outlet,
confirm earth econtinuity between earth bar and suppiers earth terminal / the electrod

If both of these are correct then:

TN-S : The suppliers earth has probably rotted off
TN-C-S : The supplier has forgotten to install the link in the cutout
TT - your earth rod (or the supplier's rod) has been nicked for scrap value, etc

 

[peter_226]

Thanks very much for your replies.

I have taken a photo (not ideal quality) of the cupboard with consumer unit and meter in it but am struggling with posting it but hopefully in due course...

In the meantime your questions seem very pertinent as I live in an old house in the country with overhead electricity supply.

I believe that SWEB rerouted the supply to connect to the new consumer unit just after it was fitted.

There is a large earth cable that comes out of the consumer unit to a connecting block from which there is an even larger earth wire which runs to the earth rod under the kitchen floor. The connections all seem in order and in reasonable condition. The rewire seems to be of a reasonable standard.

 

[peter_226]

It looks as though I will have to start another forum - I can't post an image. [/img]

 

[james 29]

Peter,

Could be a high resistance earth fault possibly on the live side. I would do the basics such as confirm polarity, loop test etc.

This is only one possible cause of course. Be careful if you disconnect any earth connections. If the fault is on the consumer side a potential will exist between the disconnected conductor and the associated earth bar.

A standard socket tester will confirm polarity.

hope this helps

 

[JohnD]

It looks as though I will have to start another forum - I can't post an image. [/img]

try //www.diynot.com/forums/viewtopic.php?t=8463

 

[peter_226]

http://i78.photobucket.com/albums/j92/Peter_22


I don't think this picture is going to be very helpful.

 

[peter_226]

http://i78.photobucket.com/albums/j92/Peter_226/DSC00158.jpg

 

[securespark]

Peter

Is that TT? I can see the supply cable coming in at the bottom, but the MET is at the top.

Does the supply come in overhead, or underground?

 

[JohnD]

... I live in an old house in the country with overhead electricity supply.

I believe that SWEB rerouted the supply to connect to the new consumer unit just after it was fitted.

There is a large earth cable that comes out of the consumer unit to a connecting block from which there is an even larger earth wire which runs to the earth rod under the kitchen floor. The connections all seem in order and in reasonable condition. The rewire seems to be of a reasonable standard.

 

[peter_226]

Hi,

The picture isn't very clear.

The supply comes in from the top of the cupboard and runs down to the left of the two white switches and into the bottom of the main fuse, then on to the meter etc.

The earth comes out of the consumer unit and is connected to the earthing block (you can just see the earthing block above the white switches) and then the earth runs down behind the cupboard behind the units below and is fastened securely to the earthing rod which is under the floor.

 

[Adam_151]

Earthing rods shouldn't be under the floor, anecdotal evidence points to the fact that such an area does not often receive a rain shower

The main CU looks like its got an RCD as an incommer, but what about those smaller boards to the side, they look devoid of any RCD

Its probably time to call an electrician in, unless you have access to (and know how to use) an earth loop tester, or an earth electrode tester

 

[peter_226]

Thanks for your reply.

This house is 350 years old and doesn't have any foundations so I believe it is quite damp under the house. Yes there is only one RCD on the consumer unit but what has this to do with the earth being live? Yes I can always call an electrician!

Excuse my ignorance but should there be an earth connection between the incoming supply (SWEB) and consumer earthing as there doesn't seem to any?

 

[Steve]

You either have a supplier earth (TN) or your own earth (TT). Never both.

And TT earths rely on damp soil for their integrity - dry soil doesn't conduct electricity. And the soil under your house will be rather dry after 350 years of being warmed by the house above.

And TT systems require an RCD on everything to meet disconnect times, as the earth loop fault impedance is often too high for an MCB alone to disconnect in time.