High value Ze

[TestEngineer]

I have an installation (TN-S system) and the Ze measure is 3,89Ohms.The start point of the installation protected by ELCB 500mA.Some final circuits protected by rcbo 30mA and the rest by mcb.I suggested to the client the replacement of the feed cable but for economic reasons this will be late for one year.My question is if the installation is safe as above and if no please give me proposed solutions.

Thanks

 

[trev]

As the DNO are under a duty to maintain any earth they provide I'd say a call to them is in order. Because it's so far above the max allowed in 7671 they should come fairly quickly. Are you sure it's a TN-S though mate? We've seen a few diy mofidications on here

 

[malcolmsanford]

Is that 3.89 ohms ? How old is the installation?

Trev quite rightly on both counts posted that if the DNO have supplied an earth they have a duty of care to maintain it, and that would be my firsr call to see if they had supplied it.

Over the years as he rightly pointed out Sparks have often done DIY TN-S systems without the DNO knowledge, if this is the case then you might have to either pay to have the system made into a TNC-S or if it's not available make the system TT.

As for existing with an upfront 500mA ELCB ( Voltage or Current?) and then 30mA additional protection I should imagine the installation is safe. I would though test the operating times of these devices

 

[Deleted member 19807]

i suspect if its got an up front elcb it has been tt (or still is)

 

[Deleted member 26818]

In the past, DNOs would install up front ELCBs where they were no longer able to maintain the earth.
I believe the practice nowadays is just to tell the customer to TT the installation.
Once installed, the ELCB became the responsibility of the customer.