Zs and more Zs

[wilkyduch]

Trying to make sense of ELI and would appreciate some help
Could anyone tell me where you obtain the value for Ze
Thanks very much

 

[JLD]

When calculating Zs you need to be able to obtain your Ze from the provider. This may however be harder than first expected and so the On-Site guide provides standard values that can be used on page 11.

TN-C-S = 0.35 Ohms
TN-S = 0.8 Ohms
TT = 200 Ohms

I hope this helps.

 

[rryles]

You measure it at the origin of the installation using a loop impedance meter.

It should be measured with parallel paths (main bonding conductors) removed. Therefore you need to isolate the whole installation first.

 

[Sparky Ninja]

At the origin.

Look in your GN3 or back at the training you've received

It's all there.

 

[wilkyduch]

Nailed. Thanks for all your help.

 

[telectrix]

When calculating Zs you need to be able to obtain your Ze from the provider. This may however be harder than first expected and so the On-Site guide provides standard values that can be used on page 11.

TN-C-S = 0.35 Ohms
TN-S = 0.8 Ohms
TT = 200 Ohms

I hope this helps.

those are maximum values. Ze should always be measured.

 

[IQ Electrical]

those are maximum values. Ze should always be measured.

Absolutely, you are proving an effective means of earthing, the ESQCR values should be limited to design figures only IMO

 

[Deleted member 26818]

those are maximum values. Ze should always be measured.

Not according to the NICEIC it appears.

 

[telectrix]

well then, those niceic bods can look at a job i did yesterday. TN-S, Ze measured at 0.29ohms with Cu isolated from supply. if i,d used 0.8, my Zs reasings would be lower than Ze!!!

 

[Deleted member 26818]

From what I understand, their argument is that EAWR doesn't allow live working.
As such the Ze and Zs tests are not allowed, as Ze can be obtained through enquiry and Zs by calculation.

 

[telectrix]

there is an argument here. " live testing is not live working". and, for safe isolation you have to pull the DNO fuse. if that's not live working, i son't know what is. and as for enquiry, i phoned scottish power 4 weeks ago to enquire if they could PME an installation. the answer was " we have no way of telling without a site visit. we will contact you within 5 working days to arrange. and what is Ze?" 4 weeks later, no site visit, no contact. pillocks

 

[rryles]

From what I understand, their argument is that EAWR doesn't allow live working.

EAWR does allow live working. It just limits when and how.

How do NICEIC recommend doing an incoming polarity test?

 

[telectrix]

with your tongue?

 

[Deleted member 26818]

Like I said, their argument is that Ze can be obtained by enquiry, so live measurement is not required.
Obviously when determining the polarity, as there is no other option than to conduct the test live, they have (as far as I'm aware) no other recommendation.

 

[IQ Electrical]

To be fair here, I've got the NICEIC testing book open here and the Ze test is as it should be.

It was Zs testing at outlets where the BS 1363 lead can not be used where calculation is recommended.

Again though, on every technical assessment I've ever done (don't ask) I've done measured Zs at luminaries etc without comment-I suppose NICEIC have to be seen to be abiding by EAWR 1989 which incidentally makes no distinction between 'work' and 'testing'.

 

[telectrix]

To be fair here, I've got the NICEIC testing book open here and the Ze test is as it should be.

It was Zs testing at outlets where the BS 1363 lead can not be used where calculation is recommended.

Again though, on every technical assessment I've ever done (don't ask) I've done measured Zs at luminaries etc without comment-I suppose NICEIC have to be seen to be abiding by EAWR 1989 which incidentally makes no distinction between 'work' and 'testing'.

wonder what their take is on lightmates then?

 

[IQ Electrical]

Lol, I've already e-mailed NICEIC to request that 'plug-in adaptors for light fittings' are mentioned in the next revision (probably due for amendment 1).

 

[andyb]

Not according to the NICEIC it appears.

Not true
Every year without fail I am asked to test Ze during my Niceic assessment.

 

[JLD]

those are maximum values. Ze should always be measured.

Good luck with measuring Ze at the design stage of a green field project. Yes Ze should be measured where possible but this is not always the case.

 

[IQ Electrical]

Good luck with measuring Ze at the design stage of a green field project. Yes Ze should be measured where possible but this is not always the case.

At the design stage we are forced to use the figures you originally quoted.