Strange Ze on a TN S

[Gringoking88]

Hi all,

Hope you are all well.

I went to do an EICR at a small domestic property supplied by a TN S today, it is wired in singles using the conduit as CPC, however, there are no lugs for fly leads to sockets or light switches. In itself, what does this warrant, C2 / C3, there are only class 2 fittings in use?

Also, upon initial check the incoming fuse carrier was smashed and needed replacing, also Ze was 0.00 with a PFC / PSCC of greater than 10 KA. I advised the client to call DNO to replace fuse carrier, sort the earth and fit an isolator, tbf they atended within a few hours, replaced the fuse carrier, but left the main earth terminal off and said to the client call me back and I can put a clamp on it, rightly or wrong, I revisited and clamped the main earth, however, carried out the Ze again and the same reading is achieved.

Can someone help explain how and why I get that reading and more importantly, how I resolve it?

Many thanks in advance,

 

[Vortigern]

For a start I would call back the DNO to suppy an earth Under Reg 24 they must do so, i.e. maintain an existing earth. They should have put a braided earth on with their spring tension clip. There is now way you should do that. Resolving 10ka PFC not a problem to resolve. CU is rated to 16ka, back up fuse anything from 16 to 33 Ka which covers your upstream OCPD.

 

[Strima]

Very close to the transformer then.

 

[Vortigern]

Did you have att off?

 

[Wilko]

it is wired in singles using the conduit as CPC, however, there are no lugs for fly leads to sockets or light switches. In itself, what does this warrant, C2 / C3, there are only class 2 fittings in use?

Hi, a domestic installation of metal conduit CPC is not common to me. And one that is done properly and in good condition throughout is perhaps rare. But if the conduit is properly bushed to metal back boxes and the Zs at each point is good and there is at least one solid fixing from the back box then it’s sufficient and no code is required in my view. For sockets there must be fly leads though?

 

[westward10]

Please tell me you didn't fit an adjustable earth clamp to the lead sheathed supply cable.

 

[Gringoking88]

For a start I would call back the DNO to suppy an earth Under Reg 24 they must do so, i.e. maintain an existing earth. They should have put a braided earth on with their spring tension clip. There is now way you should do that. Resolving 10ka PFC not a problem to resolve. CU is rated to 16ka, back up fuse anything from 16 to 33 Ka which covers your upstream OCPD.

I will do that as agree. I was just very surprised they said just get the electrician to do it. I was more surprised about the readings tbh.

 

[Gringoking88]

Hi, a domestic installation of metal conduit CPC is not common to me. And one that is done properly and in good condition throughout is perhaps rare. But if the conduit is properly bushed to metal back boxes and the Zs at each point is good and there is at least one solid fixing from the back box then it’s sufficient and no code is required in my view. For sockets there must be fly leads though?

No Fly leads anywhere and no lugs to do so, not on sockets either, just the fixing screws to give continuity.

 

[Gringoking88]

Please tell me you didn't fit an adjustable earth clamp to the lead sheathed supply cable.

I could but I would be lying, I was extremely careful not to damage the supply cable and weiging up the risks, thought it was better to an earth than no earth at all???.... Not saying I got it right but would value wiser words?

 

[telectrix]

I could but I would be lying, I was extremely careful not to damage the supply cable and weiging up the risks, thought it was better to an earth than no earth at all???.... Not saying I got it right but would value wiser words?

hold my hands up. i've done it myself a couple of times.

 

[westward10]

Fitting one of those to a lead sheathed cable is extremely hazardous. Packaging on many of these clamps state they are not to be used on this type of cable, any type of cable for that matter. It is not possible to maintain a tight connection to the cable and you certainly don't want to be in close proximity should the clamp create a fault situation within the cable.

 

[Gringoking88]

Fitting one of those to a lead sheathed cable is extremely hazardous. Packaging on many of these clamps state they are not to be used on this type of cable, any type of cable for that matter. It is not possible to maintain a tight connection to the cable and you certainly don't want to be in close proximity should the clamp create a fault situation within the cable.

Completely agree mate, but given the choice of no earth or an earth, double edged sword?....

 

[westward10]

Completely agree mate, but given the choice of no earth or an earth, double edged sword?....

Not really, never say never. Get the DNO back that is the answer.

 

[Gringoking88]

Not really, never say never. Get the DNO back that is the answer.

Agree completely with that!

 

[Wilko]

No Fly leads anywhere and no lugs to do so, not on sockets either, just the fixing screws to give continuity.

Ok, reading Reg 543.2.7 an earthing fly lead is required in each accessory. And for safety, I would say it really should be there in an outlet. So C2 from the judge with red wine in hand.

 

[Gringoking88]

Ok, reading Reg 543.2.7 an earthing fly lead is required in each accessory. And for safety, I would say it really should be there in an outlet. So C2 from the judge with red wine in hand.

Lol, I like the red wine, however, in terms of resolution, whats the most efficient way to resolve?

 

[Gringoking88]

Also just a note to say thanks for the balanced responses rather than a slatting which can quite easily occur so appreciated!

 

[westward10]

Do the back boxes have earth terminals.

 

[Gringoking88]

Do the back boxes have earth terminals.

Nope, literally just box with conduit feeding.

 

[Wilko]

Lol, I like the red wine, however, in terms of resolution, whats the most efficient way to resolve?

If the conduit and boxes really are in good shape, then perhaps drilling and tapping for a connector would be my pick.