Help please

[JustStartingOut]

Hello

Just wondering if anyone can help.

I have been to a house today to change a CU. I completed dead tests and found the following:

-> Ring circuit (originally upstairs ring) has been extended to include the kitchen, it is all wired in red and black 2.5/1.0. Problem is the (r1+r2)/4 is lower for the kitchen circuit than the rest of the ring, and it is less than would be expected from the r1 and r2 values. Is this indicative of interconnection or something else???

-> I disconnected all of the circuits from the CU and found there is continuity (although resistance >99kOhm) between the line of the circuits for downstairs lights and downstairs sockets. Shouldn't these be totally separate? There is also continuity between line and earth on the downstairs light circuit (again resistance >99kOhms) and the Insulation resistance on the downstairs light circuit is 50MegOhm.

On the live test I found

-> TN-S with a Ze of 3.4 ohms. The earth from CU to supply sheath is now <1m long and in 16mm cable. The clamp on the sheath looks like this...

http://www.flickr.com/photos/35250598@N04/3570736419/

Does the clamp need to contact the metal of the sheath, it is just making contact with something black and metallic. Do i need to put in an earth rod and make it TT as this value is too high?

Oh by the way, the main earth was previously a short length of 1mm CSA cable. So don't know if a DIYer has had a bad go at his electrics.

Any thoughts / comments very much appreciated.

 

[Apache]

oh dear

I'm no expert but you'll have fun adding a RCD or two to that!

:|

 

[batty]

I would take clamp off and carefully file sheath but be very careful. It maybe the pitch has run so cable is not making good contact. Alternatively you may find the lead sheath is shot and no longer adequate. TT is easiest option if this is the case. Who is supplier some are better than others at sorting problems they may pme it.

Batty

 

[SPECIAL LOCATION]

-> Ring circuit (originally upstairs ring) has been extended to include the kitchen' date=' it is all wired in red and black 2.5/1.0. Problem is the (r1+r2)/4 is lower for the kitchen circuit than the rest of the ring, and it is less than would be expected from the r1 and r2 values. [b']Is this indicative of interconnection or something else???

May be a ring with a branch across it.. wired as a figure of '8'

You may need to do the cross over L & N at CU and do the R1+Rn readings

as per step 2 page 81 On site guide.

-> I disconnected all of the circuits from the CU and found there is continuity (although resistance >99kOhm) between the line of the circuits for downstairs lights and downstairs sockets. Shouldn't these be totally separate? There is also continuity between line and earth on the downstairs light circuit (again resistance >99kOhms) and the Insulation resistance on the downstairs light circuit is 50MegOhm.

Yes ALL circuits should be separate from ALL other circuits!

needs a bit of serious investigation IMHO.

Possibly reading though a light or accessory wired between two circuits?

Double check EVERYTHING is unplugged disconnected.

Hidden FCU's

security lights with PIRs maybe?

On the live test I found

-> TN-S with a Ze of 3.4 ohms. The earth from CU to supply sheath is now <1m long and in 16mm cable. The clamp on the sheath looks like this...

http://www.flickr.com/photos/35250598@N04/3570736419/

Does the clamp need to contact the metal of the sheath' date=' it is just making contact with something black and metallic. Do i need to put in an earth rod and make it TT as this value is too high?

[/b']

Oh by the way, the main earth was previously a short length of 1mm CSA cable. So don't know if a DIYer has had a bad go at his electrics.

Any thoughts / comments very much appreciated.

The earth, it does sound a bit DIYish.. just looking at the "apparent home made clamp"

Do NOT change anything without permission from the DNO.

1/ I would contact DNO explain the high Ze reading you have taken.

2/ they may want to come out and check or verify stuff themselves..

or they may be happy to advise you to change it to TT..

3/ But either way let them make the decision, not you.

then your bottom end is covered!

 

[JustStartingOut]

Thank you for your replies. A phone call to DNO sounds like the first point of call.

 

[binky]

-> I disconnected all of the circuits from the CU and found there is continuity (although resistance >99kOhm) between the line of the circuits for downstairs lights and downstairs sockets. Shouldn't these be totally separate? There is also continuity between line and earth on the downstairs light circuit (again resistance >99kOhms) and the Insulation resistance on the downstairs light circuit is 50MegOhm.

Can be caused by damp especially if fresh plaster is on the walls. Also make sure you completely disconnest each circuit from the busbars before checking for links between circuits.

 

[matt.leung]

what does DNO stand for?

 

[Apache]

what does DNO stand for?

Distribution Network Operator AFAIK

 

[a1]

what does DNO stand for?

Distribution Network Operator AFAIK

That Is Correct, Patch.

 

[ianmacd]

This link may be useful too:

http://www.nationalgrid.com/uk/Electricity/AboutElectricity/DistributionCompanies/

Ian.

 

[green-hornet]

May be a ring with a branch across it.. wired as a figure of '8'You may need to do the cross over L & N at CU and do the R1+Rn readings

as per step 2 page 81 On site guide.

Yes ALL circuits should be separate from ALL other circuits!

needs a bit of serious investigation IMHO.

Possibly reading though a light or accessory wired between two circuits?

Double check EVERYTHING is unplugged disconnected.

Hidden FCU's

security lights with PIRs maybe?

The earth, it does sound a bit DIYish.. just looking at the "apparent home made clamp"

Do NOT change anything without permission from the DNO.

1/ I would contact DNO explain the high Ze reading you have taken.

2/ they may want to come out and check or verify stuff themselves..

or they may be happy to advise you to change it to TT..

3/ But either way let them make the decision, not you.

then your bottom end is covered!

I agree 100%

Just a warning to everyone here most DNO's will if they deem necessary prosecute any electrician who it feels has tampered with any mains cable.

This means cutting back any outer cover to attach an earth clamp.

If you find any high/suspect earthing do as special location has said and call them, and only change or do work with their permission, ask them to send written confirmation of the permission given.

The service is free, and is a major safety issue and shows your commitment to the customer.

 

[JustStartingOut]

Thanks for your replies. I called DNO out (E-On) who came within 40 mins and added a new earth terminal to replace the dodgy clamp which was in contact with the supply cable armour.

They connected some copper braid and a conector block to the lead sheathing of the supply. Only took about 10 mins and was free Pray

Ze is now 0.14 ohms, down from 3.4 ohms.

Thanks again.

 

[green-hornet]

Thanks for your replies. I called DNO out (E-On) who came within 40 mins and added a new earth terminal to replace the dodgy clamp which was in contact with the supply cable armour.They connected some copper braid and a conector block to the lead sheathing of the supply. Only took about 10 mins and was free Pray

Ze is now 0.14 ohms, down from 3.4 ohms.

Thanks again.

Thats how inportant earthing arrangements and the lack of them are.

Glad to see you took the correct measures and made safe another dangerous installation.

 

[batty]

I am glad this all worked out ok. The reason I said I would do the job myself is because I am used to dealing with EDF. They will not put in isolation switches so you have no choice but to do the job yourself. It can take them up to a day to come out in an emergency this is a fact. I am glad other providers are giving a better service.

Batty

 

[green-hornet]

I am glad this all worked out ok. The reason I said I would do the job myself is because I am used to dealing with EDF. They will not put in isolation switches so you have no choice but to do the job yourself. It can take them up to a day to come out in an emergency this is a fact. I am glad other providers are giving a better service.Batty

Batty, you must report any delay in your requests to a DNO, to your scheme provider.

All Part P providers are in the process of asking for extra powers to enable DI's to do temperary disconnections and reseal after connection.

There are trials running at the moment to implement such extra powers.

However any case for improvement will only come from the ability to show the lack of immediate action taken from any DNO and the waiting times imposed for such emergency remedial actions you may request.

If no one complains, then they will see this as admittance that the DNO's provide a competant service.

 

[Evans Electric]

Thanks for your replies. I called DNO out (E-On) who came within 40 mins and added a new earth terminal to replace the dodgy clamp which was in contact with the supply cable armour.They connected some copper braid and a conector block to the lead sheathing of the supply. Only took about 10 mins and was free Pray

Ze is now 0.14 ohms, down from 3.4 ohms.

Thanks again.

Blimey that was good service . I hope someone from Central Networks reads this.

 

[druid]

good for you JustStartingOut on getting the dno out and sorting your prob, im in a similar situation with eon and if poss could any1 say which is the best number to ring and what to say to get them out that quick to put the braided clamp on a tns sheath much obligedray

 

[Sidewinder]

druid,

Welcome to the forum.

IF you are in Wales and in WPD area then unless it is a dangerous situation WPD guidance is that they do not touch 951 clamps on the outer of TNS supplies.

To sort a 951 on a TNS then it may mean a cable cut in the street a repair then re-joint underground.

IF I understand correctly your situation relates to the incoming cable prior toDNO cut out, which would be nothing to do with the electricity provider e.g. EON, British Gas, etc. it would be the DNO which depends on your area, round by me WPD, so ring their emergency number and inform them of the situaiton - 0800 052 0400.

Could be EON, depending on your area check here:

National Grid: Distribution Network Operator (DNO) Companies

 

[ProDave]

Just to agree with everyone else, you should not ever tamper with the incoming cable.

Calling the DNO was the correct way to proceed, and they sorted the earthing problem.

If you had tried fitting your own replacement earth clamp, and things had gone wrong you could be in deep trouble.

In cases like that, you usually get the DNO out quicker if you tell them it's a safety issue, and I don't think many would argue that a poor earth was not unsafe, so would be entirely justified in this case.

 

[druid]

thanks sidewinder and prodave, dont worry, no way am i goin to touch the clamp as very dangerous and as you say is responsibility of d.n.o, would be really resolved if i could get the d.n.o out to put proper hepwoth braided clampthanks for your advice druid