This seems very dangerous...

[Dave_]

Went to a house today fault finding, RCD tripping....

Faulty RCD but thats not the issue.

I noticed that there didnt actually appear to be a main earth.

The supply upstream of the meter and teleswitch (now out of use) is a pyro that is a single core 10mm with a strap on the sheath that provides the NEUTRAL (no earth in sight!)

The mains position including the meter, DB & teleswitch was moved around 5 years ago by what the client claims is a competent spark who had all the papers and did provide paperwork at the end of the job. I asked for the paperwork but client said could be difficult to find it. Meter seals and teleswitch seals cut in all the places needed to move the equipment.

Im guessing that the flat was originally supplied with 2 single core 10mm pyro's and some numpty has snapped one when moving the mains to its new position then not done the proper thing of reglanding the pyro, or whatever he needed to do safely get it back in service.

If that is the case that pyro is buried under the floor in a wall somewhere now. I tried to access the mains intake cupboard. Not FB keylock, need to now contact the council. I need to see that cupboard as if there were two 2 SC pyros then ill find he has had to connect the sheath of the one in service to the neutral bar. There is probably a Ryefield cupboard there.

All in all though the client is gonna get a huge bill as its the DNO that is going to have to put it right as its all upstream of the meter so im not touching it.

I took a few readings. Im guessing its a TNS system as its a 60's block with pyro supply. ) 0.29 ZS. Cant do a ZE as there is no earth! Your probably wondering what is providing the earth? Its the cooker CPC, connected to a gas hob connected to the gas supply. there is bonding in place. But basically they are relying on the gas pipes as a main earth.

I told the client its very dangerous and if I rang NICEIC technical they would most likely advise to isolate the installation. Its been like this for 5 years (no excuse i know!) I didnt switch it off but said ill be back tomorrow with Hackney council to get in the cupboard and find out exactly what is going on.

Any thoughts on this??

 

[Knobhead]

The Pyro sheath is the CPC. Use that to do you're tests. As for single core Pyro, never seen it.

 

[londonlec]

Ive seen this before, and I questioned it.

Various council estates in North London have this method, still in service. 10mm single core with the sheath (PVC insulated) as the earth/neutral conductor.

Edit: Hackney council probably own this cable, so it should be them responsible for maintaining it, but I doubt they will do anything with it to be honest.

 

[Dave_]

I did wonder if it was acting as a PEN conductor but the strap goes from the pyro sheath through the meter then straight into the main switch. nothing goes to the earth terminal whatsoever.

 

[londonlec]

I did wonder if it was acting as a PEN conductor but the strap goes from the pyro sheath through the meter then straight into the main switch. nothing goes to the earth terminal whatsoever.

The ones I have seen have the pyro glanded into an adaptable box, where the link is made between N and E, then Live Neutral and Earth go off into the CU.

(Good luck with the council :86: !!)

 

[snowhead]

nothing goes to the earth terminal whatsoever.

It probably did before the Unauthorised move.

 

[londonlec]

It probably did before the Unauthorised move.

Whoever moved it must have had access to the intake to isolate the supply, and I'm pretty certain Hackney have stopped using standard FB keys on their doors.

 

[Dave_]

Hopefully it is just a PEN conductor then and needs splitting. Ill check once I can get in the ryefield cupboard tomorrow morning!

 

[londonlec]

Let us know the outcome Dave. If your struggling with access, collar the caretaker ;-)

 

[Dave_]

Apologies for the late reply! I forgot...

I visited site the other evening to discover it was a PME system. At the service head there was three pyros that were single core 10mm each with 2 pyro straps around the sheath one to neutral bar one to earth, then obviously connected together.

Easy job - just a case of connecting supply neutral to MET at the CU. retested Ze and got 0.19 not 1.19 or thereabouts!

Makes sense I suppose. That pyro lateral main being a concentric cable, and I suppose the sheath can take a whopping amount of current.

 

[Guitarist]

Don't you just love a happy ending.... :wub:

 

[LlandrilloSpark]

Never seen anything like this on the sunny North Wales coast!

 

[cobrauk]

If this cable is upstream of the meter then its on the clients side then there is no way you should combine earth & N only the supplier can do that or have i misread the OP ?

 

[Dave_]

CobraUK,

You have clearly never dealt with Hackney Council.

 

[cobrauk]

No only with company's that follow the regs it seems lol