High ze and circuit zs ????

[sidekick]

Urgent advice please.

I have done a consumer unit change where the main earth is 10mm and meter tails are 16mm.
I have connected new 25mm tails on consumer side of isolator switch and 16mm main earth to single pole block onto DNO 10mm earth.

Problem I have is a Ze of 0.54 and PSCC of 10KA. Is this something I can correct or is it a DNO problem?

Zs on all circuits is within limit except oven circuit which is 1.52 against max permitted 1.44.
Obviously will come down if Ze does.

[pennywise]

what earthing system is it?

[sidekick]

what earthing system is it?

Originally thought TNCS but need to take back of kitchen cupboard out tommorrow as it is concealing very old metal clad enclosure and could be TNS ?
Main earth can be seen clamped to incomming cable below the cupboard.

[sparks1234]

If its TNS then no problem, max of 0.8 allowed

[pennywise]

I think you may find it to be TN-S having a look should confirm it and if thats the case it's within 0.8.

[sidekick]

If its TNS then no problem, max of 0.8 allowed

Thanks Sparks 1234 and Pennywise.
Ok with the 0.8 for TNS but this still gives a problem with Oven circuit which has Zs 1.52 against max permitted of 1.44 ?

[sparks1234]

can you lower the breaker at all?

[JASON]

Well, if you go by the regs then you would be ok as the CU you have just installed will have full RCD protection, which allows 1667 ohms.

[sidekick]

can you lower the breaker at all?

Not sure of the cooker rating. Very old free standing unit.
6mm T/E used from 32A breaker and cooker switch has a socket.

Would lowering to 16A create tripping problems ??

Long term the Client has sumitted plans to extend property and the kitchen will be moved with new circuits and appliances.

[sparks1234]

depending on make of board, you can order 25 amp MCB,s, alternatively if you cant get one to fit the board you could put an enclosure next to the consumer unit and down rate it slightly, that is if the cokker loading allows

[sidekick]

Well, if you go by the regs then you would be ok as the CU you have just installed will have full RCD protection, which allows 1667 ohms.

Thanks Jason.
17th ed high integrity cu fitted.
With the intended plans to extend and relocate kitchen etc. Is it enough to just comment on the high reading on the cert and leave it at that. ?

[sidekick]

depending on make of board, you can order 25 amp MCB,s, alternatively if you cant get one to fit the board you could put an enclosure next to the consumer unit and down rate it slightly, that is if the cokker loading allows

An additional enclosure next to cu not really an option as just fitted 17th ed high integrity 15 way board to allow for all future build plans on property at client request to avoid all seperate enclosures and add ons etc. Do wylex do 25A

[JASON]

Thanks Jason.
17th ed high integrity cu fitted.
With the intended plans to extend and relocate kitchen etc. Is it enough to just comment on the high reading on the cert and leave it at that. ?

Yes you can and i expect you will need to include the cost of a new radial for the cooker when the other works are being done.

[pevvers]

So your R1+R2 on a cooker circuit is nearly a whole ohm?!

What CSA is the cable, and how long is the run?

[Bromd123]

Couldnt this be caused by a bad termination? at the cooker point?