An interesting read

[andrew1210]

OK, before I start, if you get confused, don't worry, 8 different people from Scottish Power are!

Following our RCD and next doors tripping in sync for no apparent reason I called an electrician to take a look, refer to
//www.diynot.com/forums/viewtopic.php?t=207456 from last Jan for more info!

Electrician came out, no problem, connected a 'megger' passed, tripped at 28mA..... IR test pass etc etc..... turned off main RCD ..... and connected ammeter to main incoming earth... 2A on earth incoming!

Phoned SP, they treated the call as an emergency, within 4 hours which actually turned into 4 weeks due to snow, SP came out today.

Yep, 3A now on incoming Earth, fluctuating and intermitenetly rising to 7A

We feed next doors supply (semi-detached) so they pulled the service fuses in both houses (and broke ours so a nice new one now) and 3A was still present.

Now the tricky bit, our supply is overhead and SP claim there is NO EARTH provided by them and local spikes should be installed, none of the 8 houses in our street have them! after checking 4 random houses, all earths are joined to DNO's neutral at the cutout. Then SP checked earths on two more houses on same phase, 2-5A on all Earths.....

They hit a spike into our grass and ran a lead to our Earth, and the phantom current disappears, they think it is on their neutral

They have left after a full day not having a clue what is going on here after 8 men have been out today. Houses earths are tied to their neutral, schmatics of the setup show no Earth on DNO side, yet there is what they think is an earth cable on the poles

Just thought i'd give everyone a read tonight and let you try and get your head around it!

 

[1john]

They say you have no earth and you say you have 3A on it?

 

[andrew1210]

They say we have an Earth wire, but it is connected at the service head to the DNO's neutral as are 4 other houses checked.

Only problem is, SP have found 3A on the Earth wire in the Service head

CU-------Service Head (Earth joined here to neutral)------ Pole Outside
3A showing here on earth (with main switch off and Service Fuse out)

 

[1john]

So you have a PME (tnc-s) supply, was this converted from a TT system? Is there a wire running down the pole to a spike? What was the Ze?

 

[viewer]

Just because earth cables drop down the poles doesn't mean that the PME system is working. Dry ground, broken connectors etc etc can mean that there is no working (low resistance) earth. This doesn't in itself explain anything. When they said 3A (sure it wasn't 3V?) the current must be flowing from the earth wire to somewhere else. Where? and how can it if the fuse is pulled? Only thoughts are that someone has a solar panel, battery backup or similar which is incorrectly wired. Please let's know what transpires tomorrow.

 

[andrew1210]

Hi not sure of the Ze value, will ask tomorrow

They say all houses are wired up as PME, but outside wiring, and SP Schematics suggest TT.

We have overhead poles on the opposite side of the street, with a thick black cable running down the side of each one, going underground and feeding two two blocks (four houses) The transformer is at the top of our street and they "think" there is an Earth spike there but not sure as no schematics available for it and could bot visually see it due to the dark and overgrown shubbery!

They are goin to investigate tomorrow in daylight, by pulling service fuses in each home (8 on the phase) and see when this phantom 3-6A dissapears from everyones Earth.

I am not sure what a Ze value is but if it is any help, they said although we are connecred to neutral wee show as having a very strong earth!

I am an amateur and can usually get my head around these things but i am beat, TMI going about in my opinion

 

[andrew1210]

@'viewer'

Deffinately 3A not volts. this is why they are concerned and it is appearing on all houses on the phase. I cannot understand it either.

Will certainly post the outcome tomorrow night (at school during day)
SP are goin to have a poke around at the transformer tomorrow as it 'blew up' last year and was rewired, they think there may be a problem there.

 

[westie101]

Scroll down to the bit about net currents, there is a lot of info on this site about them (I've measured 7.5 A)

http://www.emfs.info/Sources+of+EMFs/distribution/

 

[andrew1210]

that is a very interesting read, sounds like what is happening here, possibly earthing through utilities as all are underground and are iron water and gas etc. we are also only about 25m away from local substation/transformer.

Have printed this and will show them tomorrow.


Thanks

 

[echoes]

If they are measuring 3A on the main earth cable in the cut-out, that same 3A must be flowing either via the CU, or through the gas/water pipe bonds. There must be a circuit somewhere for the current to flow.

 

[andrew1210]

I thought that, they asked if we have been receiving tingling shocks from appliances but we have not. they also disconnected the earth and tested it seperately after putting us on a tempo. Earth spike.

This 3A is apparent in our house and 4 neighbours

 

[andrew1210]

I'll give in for the night thinking about it, lol

Will wait and see what SP have to say about it tomorrow

They are sending a cherrypicker to look for a cracked something-or-another on the pole we are fed from which they think they saw in torchlight tonight.

A very strange and confusing one though.

 

[1john]

Post their findings if you would.

 

[bernardgreen]

This seems to have all the symptoms of the network neutral being opened circuit between the houses and the transformer.

Possibly the star point of the transformers is properly grounded. But the star point is not connected to the neutrals at the houses. Failed cable or other fault in the network.

This wouldn't be a problem if the loads on the phases were equal as there would be no current in the neutral returning to the transformer.

But the loads were not balanced so the neutral would have current from the un-balanced phases and this appears to be making its way to the transformer via the ground. Its is using any connection between neutrals in houses that are connected to the CPC of the house,

 

[andrew1210]

Will do, theres an event after school that I am helping to run so I won't be in until about 7pm, will deffinately post findings though, I eagerly await the results myself!