High Ze on tns supply

[Dave123]

High Ze on a tns supply. It’s 1.48 ohms. Weird as I did a Ze here 4 weeks ago and it was 0.50.

Do DNO come out for a Ze that high what is likely to happen when I call them?

Thinking of going home to double check tester is working ok at home before I call them.

Thanks

 

[Dave123]

It’s all 30ma rcbos so it’s not unreasonable for it to be left on in my opinion.

Thanks

 

[UNG]

High Ze on a tns supply. It’s 1.48 ohms. Weird as I did a Ze here 4 weeks ago and it was 0.50.

Do DNO come out for a Ze that high what is likely to happen when I call them?

Thinking of going home to double check tester is working ok at home before I call them.

Thanks

Do you have reason to doubt your tester?
If you did a Ze 4 weeks ago and you now have a reading that is 3 times higher you could have a developing external fault I would certainly call the DNO and report it as the supplied earth Ze is now higher than is allowed

It’s all 30ma rcbos so it’s not unreasonable for it to be left on in my opinion.

Thanks

Could be a dangerous assuption to make as technically you are leaving an installation with a known fault that could result in the premises losing it's earth connection some time in the future

 

[pc1966]

Thinking of going home to double check tester is working ok at home before I call them.

Presumably you are not using a no-trip low current test?

To check the MFT do a Zs test with both E & N probes to N.

You should get more or less the same PFC and PSCC and they ought to be comparable to the expected supply characteristics. For example, if you have 10% max DNO side drop on a 60A supply then the PSCC should be at least 600A.

 

[happysteve]

Definitely worth letting the DNO know, they will be pleased to receive the info. In a similar case (albeit lower readings of about 0.55 to 0.62Ω on a TN-C-S) I spoke with the client and explained the situation with them, and got their agreement to give their contact details to the DNO.

 

[UNG]

Definitely worth letting the DNO know, they will be pleased to receive the info. In a similar case (albeit lower readings of about 0.55 to 0.62Ω on a TN-C-S) I spoke with the client and explained the situation with them, and got their agreement to give their contact details to the DNO.

I call the DNO quite a few times a year with earth faults on one occasion the external earth fault on the property I was working on was actually found to have left half the properties in the street without an earth.
I don't give the client the option it isn't safe and this is what is going to happen if they don't like it then they called the wrong electrician you can't walk away from serious faults

 

[Dave123]

So I drove the 10 minutes home and and did a Ze at home which was 0.12 so I was happy it wasn't the tester. Rang DNO and they arrived within a few hours and said my Ze was correct and they will dig up the road in the next 2/3 days to fix it. Thanks for the input I was just intriged what people had experienced before when have similar issues.

 

[Dave123]

Do you have reason to doubt your tester?
If you did a Ze 4 weeks ago and you now have a reading that is 3 times higher you could have a developing external fault I would certainly call the DNO and report it as the supplied earth Ze is now higher than is allowed

Could be a dangerous assuption to make as technically you are leaving an installation with a known fault that could result in the premises losing it's earth connection some time in the future

I meant it wasn't unreasonable to leave the property till it could be fixed by the DNO as it had Rcbo and the Ze was 1.5 so it would not be that different from a TT.

I guess you'd turn the power off for 2/3 days in this case then as its a dangerous assupmtion?

 

[davesparks]

It’s all 30ma rcbos so it’s not unreasonable for it to be left on in my opinion.

Thanks

But what if the neighbours don't have RCDs?

 

[Dave123]

But what if the neighbours don't have RCDs?

Oh So I should of turned off the neighbours power too while we wait 2/3 days for the road to be dug up. They would love that.