Loop impedance is 0.55

[Spark123]

Depending on the supply type, the connection between the DNO knockout and the MET (main earth terminal) on a normal 100A supply with 35mm² tails is normally 16mm² -you may need to get DNO to do this.

Sometimes, the screws or allen grubs are exposed, and you can connect a piece of 16 milli yourself, should you wish to.

Fair game if the DNO has left the terminal accessable to connect to.
I remember recently seeing some pictures somewhere else where it shows putting a DIY hole in a DNO cutout for access to an earth Please note that it is illegal and dangerous for anyone other than the DNO to tamper with the DNO equipment.

 

[dingbat]

RF, that would be a classic Leeds job except for one thing...


...you wouldn't normally even see a clamp on the sheathing!

 

[greencoat]

Here's what the setup looks like from mobile phone photo.



http://img117.imageshack.us/img117/8094/photo0063dx1.jpg and

http://img117.imageshack.us/img117/4876/photo0065sc8.jpg


In second photo, the earth at the bottom of pic is some bonding from a nearby water pipe, not currently connected to anything. The DNO fella added the isolator so that the spark could do the work and just connect the tails without the need for the DNO to come out. (is what he said) But Where is the MET on this system? And is this a TNCS type? or TT now?

hope they show enough.

Many thanks
Pete

 

[securespark]

Can't see the crucial bits - what's happening with all those earths at the bottom.

What does that warning label say?

If it were TN-C-S, there would be a bit of 16mm2 from the cutout to the MET.

If it were TN-S, there would be an earth connection to the cable sheath.

You may have TT. Does your cable come from overhead? If so, you'll need a rod in the ground. You can still have TT as an underground cable. Do you live in Staffs?

 

[greencoat]

Securespark,

that earth at the bottom of the pic bonded the water pipe to the cable/sheath underneath the old Service fuse by a metal tag, but then the Service fuse was changed to what is in the pic now and I can't remember where the earths went. The original service fuse had a strip on the side with several screws in, the earth from the CU went into it, but looked like it should have had a cover on it.

When the next DNO spark came to reset the card meter, he got a high reading, then moved the card meter, fitted the isolator and left the 2 earths loose.

This is a better view of that earth at the bottom

http://img295.imageshack.us/img295/3839/photo0075ef2.jpg

The warning label is just an emergency contact no. for Scottish Power, I live in Merseyside.

As far as I can tell the cable is from underground.

I don't know where he tested the earth loop impedance though. I'm sure I heard him plug something in to a socket in the kitchen while I was upstairs.

So I don't know;

a) what type of system it is
b) whether to get a spark to have a look or
c) get someone to inspect & test it & see just what is needed.

Any advice is much appreciated. I haven't had power in the property since last Monday. Just 3 visits by the DNO sparks.

Pete

 

[securespark]

When you say "the service fuse was changed", do you mean just the fuse, or the whole thing?

If there is no earthing arrangement present, and the cable is underground, I would assume it is TT.

What does the DNO say it is?

As I said before, if it does not have earth coming from sheath or cut-out, then it probably is not TN-S or TN-C-S.

Have you got a spike outside?

Have you verified that the loose earth conductor is your MEB?

If you have TT, you are advised to fit a spike with a reading <200 Ohms, MEB's to G & W and any other services, and a split-load board with 100mA (min) TD on the incomer.

 

[greencoat]

The whole thing was changed, although the new one looks pretty similar to it. Old one was brown, new one grey.

When I asked the man who changed it, he said it was a PME type. The second man who came to reset card meter & ended-up swapping it all about did the test, but didn't say anything about what type it was. He just said that I'd need a spark to sort the earthing out because of the high reading and that the earths look too small. Then that I may need an earth rod or if the sparks wanted, they could use the neutral as an earth, as he pointed to the service-fuse.
(I'm not a spark so I'm struggling with some of this.)

Previously, I think there was a metal tag on the underside of the service fuse, on the sheath, like on RFlighting's pic. Does this mean that the DNO spark has changed the type of system now if this earth on the sheath was taken-off? Say, from PME to TT now?

There is no sign of a spike anywhere.

I know that the loose earth conductor is attached to a tag on my cold water main about 3 feet away. Is that what you mean by verified?


Many thanks for your help & advice

Pete

 

[Big_Spark]

Greencoat, couple of points..

Firstly, it is unlikely that the Guy who changed your meter is a spark, just a trained up monkey.

Secondly, the Earthing arrangements at the supply are the LEGAL RESPONSIBILITY OF THE DNO, as has been stated by previous posters.
From the pictures you have posted the head is certainly a PME head (TN-C-S), however that does not mean the cable is PME, but looking at the cable feeding it, I would suggest it likely is and the man who installed it has simply forgot to install a Main Earth Link from the head to an Earthing block.

No Electrician in the country, unless paid by the DNO, is legally allowed to attach anything to the head (Yes I know we all have done in the past).

The legal responsibility for your Main Earth is that of the DNO, phone them up and state this, tell them their Employee has left your installation in an unsafe manner, has not complied with their legal responsibilities and that if it is not put right within 24 hours you will contact your local trading standards and look at legal action via OffWat.

You should not spend a single penny on this problem.

 

[Steve]

Ask the DNO if PME is available where you are. This is, by far the best earthing system available, and will normally be provided by the DNO if it is available. This is what the DNO men meant by connecting the earth to the supply neutral. Neutral is earthed along its route to the substation, so provides an ideal earth point, with very low resistance.

What you had before, sounds like TNS, which is an earth derived from the sheath of the supply cable, or a seperate earthing conductor altogether. This is the second best sort of earth, and again is the DNO's responsibility to maintain.

The last resort is TT, which uses an earth electrode in the soil outside, or underneath, your property. These have high resistance (which can vary according to the dampness of the soil and the sructure of the soil), and therefore the installation requires additional protection by an RCD, in order to meet disconnection times.

 

[Chris.J]

Sounds to me as if you were on PME, otherwise you would'nt have had an earth wire from your CU MET to the service head. Then, between them, the two DNO men have decided their earth is not good enough, and so have told you to get your own man in to convert to TT. If the first one left you with power but without an earth, then I would have thought he would have been for the high jump?

 

[greencoat]

oops

 

[greencoat]

Thanks for replies.

If the house needs a rewire though, and I'm thinking it's been c. 15years, will the DNO bother to send anyone to do anything until any work is done?

I mean the DNO spark did say that the earths were too small for the house and I can't say that it's been left in an unsafe manner because it's been left unconnected.

Also, as I said in my 1st reply to plugwash, the DNO fella wrote that " recommend full NICEIC test supply to isolator only" .
Doesn't this suggest he's happy with their own earth?

Pete

 

[securespark]

Secondly, the Earthing arrangements at the supply are the LEGAL RESPONSIBILITY OF THE DNO, as has been stated by previous posters.

Surely this is only true where they have provided an earth terminal in the past, they have a responsibility to maintain it? And it certainly isn't true of TT.

One of my lads went round to inspect a PME install, and the main earthing conductor was missing. UU refused to reinstate without a cert & dosh, saying that anyone could have disconnected the conductor (the terminals were exposed).

 

[greencoat]

Just contacted the DNO to get their earth sorted so that my spark can do an inspection & test to see exactly what's needed.

Thanks for all your advice,
it is very much appreciated


Pete