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.

 

[UNG]

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.

A TT has an earth rod that you can inspect and verify it's condition with a TNS earth fault you wouldn't know if the flaky earth would stand up to a high fault current so there is a difference

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

The 2 DNO's where I'm based generally work on a 2 hours to site response when an earth fault is reported and if a dig is required it is done that day so you have guessed wrong

When I find faults like that the call to the DNO is in straight away

 

[UNG]

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.

Well you might have a looped supply so the earth fault could be in the neighbours property

 

[davesparks]

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.

Why did you turn your customers power off for 3 days? That's a ridiculous reaction to the situation!

No I'm not suggesting that you turn anyone's power off for any length of time, I'm suggesting that the responsible thing to do is inform the DNO of the situation as this may have a wider impact than just your customer's installation even though your customer's installation is safe thanks to the presence of RCDs.

 

[Dave123]

A TT has an earth rod that you can inspect and verify it's condition with a TNS earth fault you wouldn't know if the flaky earth would stand up to a high fault current so there is a difference

The 2 DNO's where I'm based generally work on a 2 hours to site response when an earth fault is reported and if a dig is required it is done that day so you have guessed wrong

When I find faults like that the call to the DNO is in straight away

It wasn’t a guess it is what happened. They came out within 2 hours but said they are too busy too dig up the road so it will take 2/3 days till it’s done. So you’d leave elderly people for 2/3 days with no power in there house?

I know it’s different to a TT but you can have 20 ohms on that so In this situation whilst waiting a few days all you can do.

 

[davesparks]

So you’d leave elderly people for 2/3 days with no power in there house?

Who has turned the power off to a house for 2/3 days?

 

[Dave123]

Who has turned the power off to a house for 2/3 days?

The other guy was saying I was wrong when I said. I don’t think it’s unreasonable as they have rcbos and 1.5 ohms that they continue to have power whilst waiting for the problem to be fixed. He said that’s a dangerous assumption. In my eyes it’s the only option whilst waiting.

I was only asking what peoples experiences were with DNO in this situation. Always a few people who criticise on forums haha they probably don’t even own a tester or a screwdriver.

 

[UNG]

It wasn’t a guess it is what happened. They came out within 2 hours but said they are too busy too dig up the road so it will take 2/3 days till it’s done. So you’d leave elderly people for 2/3 days with no power in there house?

I know it’s different to a TT but you can have 20 ohms on that so In this situation whilst waiting a few days all you can do.

So you are now changing the story

You originally posted this

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.

And then this

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

Inferring that you were leaving site without contacting the DNO and leaving a possibly unsafe installation

Now it appears you did contact the DNO they attended site and you are now waiting on them to carry out the necessary repairs so you have passed the problem on to them and they obviously see no reason to expedite an immediate repair so any problems that result from the poor earth is down to them now

So it totally changes the outcome of what you originally posted and any comments made thereafter

 

[Dave123]

I wrote the post when I was there as was surprised by the results changing over a few weeks, I’ve never had that I think it is a strange coincidence and wondered what peoples experience of DNO in that situation. Drove down the road tried my tester at home to confirm it was fine and then rang them, I wouldn’t of gone to check tester if I hadn’t done the test a few weeks prior and it ok. My point about the Rcbos was until the time it’s fixed I didn’t expect them to visit as quick as they did.

Thanks

 

[UNG]

I wrote the post when I was there as was surprised by the results changing over a few weeks, I’ve never had that I think it is a strange coincidence and wondered what peoples experience of DNO in that situation. Drove down the road tried my tester at home to confirm it was fine and then rang them, I wouldn’t of gone to check tester if I hadn’t done the test a few weeks prior and it ok. My point about the Rcbos was until the time it’s fixed I didn’t expect them to visit as quick as they did.

Thanks

In circumstances like you have experienced I usually knock on a few of the neighbours doors and explain what I have found next door and ask if they will let me do a quick Zs or Ze test, it is not unusual to find similar issues affecting more than one property or a large portion of the street

 

[davesparks]

The other guy was saying I was wrong when I said. I don’t think it’s unreasonable as they have rcbos and 1.5 ohms that they continue to have power whilst waiting for the problem to be fixed. He said that’s a dangerous assumption. In my eyes it’s the only option whilst waiting.

I was only asking what peoples experiences were with DNO in this situation. Always a few people who criticise on forums haha they probably don’t even own a tester or a screwdriver.

That's not how it came across in your post, it read as though you were saying that it is not unreasonable for it to be left on as it has all RCBO's.

This comes across as you saying that nothing needs to be done about the high Ze at all because the RCBO's provide fault protection. It comes across this way as we all know that you simply cannot just turn a customers power off, regardless of what fault you have found,