High zs readings low ze readings

[Guest77]

Re: High zs readings low ez readings

I'm not sure a live zs test is more accurate than calculating by adding r1+r2..every meter will give a totally different zs reading but if you test r1+r2 using continuity test using 5 different meters you get similar results. Live zs tests are a bit of a joke i think we all know it

I disagree, I would only calculate ZS if all other avenues were closed, testing ZS with an instrument is the proper way and the tried and tested way, calculation the lazy unaccurate way and the last resort IMHO.

 

[stevethesparks]

Re: High zs readings low ez readings

I don't think many testers give a very accurate reading utilising the no trip setting, IMHO the no trip test is a poor substitute for the high current test to seek out poor connections that a low current test may not find.

 

[shanky887614]

Re: High zs readings low ez readings

I don't think many testers give a very accurate reading utilising the no trip setting, IMHO the no trip test is a poor substitute for the high current test to seek out poor connections that a low current test may not find.

a zs test is not trying to find poor connections though, thats what your dead tests are for before you even power up the board.

the zs is purely to measure the earth fault loop impedance and calculation is a last resort.


how do you know the value provided by the dno is acurate? there could be no cpc at that property and you wouldnt know.

your testing ze anyway so why not a zs

 

[GMES]

Re: High zs readings low ez readings

This is the worrying thing now though, the new guys coming through are being told by the training centres to calculate zs, because they are trying to limit the whole live testing part. Crazy if you ask me!!!

 

[shanky887614]

Re: High zs readings low ez readings

This is the worrying thing now though, the new guys coming through are being told by the training centres to calculate zs, because they are trying to limit the whole live testing part. Crazy if you ask me!!!

that is the thing, when i did my am2 most tutors told the students to calc zs.

the examiner quite rightly so was adamanent that they either do a live ze/zs correctly or they instantly fail that part, fair enough really

 

[stevethesparks]

Re: High zs readings low ez readings

a zs test is not trying to find poor connections though, thats what your dead tests are for before you even power up the board.

Why is a Normal Zs done at a high current then?

 

[stevethesparks]

Re: High zs readings low ez readings

your testing ze anyway so why not a zs

I thoroughly recommend a live Zs is performed, I was giving an opinion that most readings given by the no trip test (low current) are generally not accurate.

 

[davesparks]

Re: High zs readings low ez readings

a zs test is not trying to find poor connections though, thats what your dead tests are for before you even power up the board.

Strictly speaking none of the impedance tests are trying to find a poor connection, they are proving a good connection throughout the circuit(s), but the high current loop test is the most likely to find a poor connection as it passes the most current and this causes the most heating of that poor connection.
It's similar to the 5second 25A bond test on a pat test identifying poor connections of using a high current ducter to test busbar/switchgear/conduit joints

 

[Badged01]

Re: High zs readings low ez readings

I guess providing you can convince yourself that you've satisfied the requirements for "live" working under Reg 14 of the EAWR's, live test Zs away rather than calculating ........

 

[davesparks]

Re: High zs readings low ez readings

I guess providing you can convince yourself that you've satisfied the requirements for "live" working under Reg 14 of the EAWR's, live test Zs away rather than calculating ........

It's live testing which is vital to proving the safety of an installation being carried out by a trained electrician. It is impossible for the work to be done dead!

 

[shanky887614]

Re: High zs readings low ez readings

It's live testing which is vital to proving the safety of an installation being carried out by a trained electrician. It is impossible for the work to be done dead!

zs is a very safe test to do thanks to lightmate and plug in socket adapter fof tester

 

[Badged01]

Re: High zs readings low ez readings

It's live testing which is vital to proving the safety of an installation being carried out by a trained electrician. It is impossible for the work to be done dead!

Rubbish, its not impossible! Assuming you've done a 1 off "live" Ze test to prove earthing is present, how does a "live" Zs test for each circuit prove "safety" more than dead testing of (R1&R2) and calculating with measured Ze? BS7671 gives you the option of measure or calculate for Zs. Infact you could argue you measure Ze, measure (R1&R2) and by calculating you have a measured Zs!!

I think you would be hard pressed to convince a H&S investigation that it was necessary to "live" test Zs in a domestic premises and not follow reg 14 of EAWR's. You could argue commercial/industrial may need "live" Zs where operational commitments mean you can't power down circuits, hospitals being a classic case.

zs is a very safe test to do thanks to lightmate and plug in socket adapter fof tester

But not 100% safe which a "dead" (R1&R2) should be for the trained electrician!!


....... oh, and its nice to be back for a fleeting visit to add some contention to debates

 

[davesparks]

Re: High zs readings low ez readings

Rubbish, its not impossible! Assuming you've done a 1 off "live" Ze test to prove earthing is present, how does a "live" Zs test for each circuit prove "safety" more than dead testing of (R1&R2) and calculating with measured Ze? BS7671 gives you the option of measure or calculate for Zs. Infact you could argue you measure Ze, measure (R1&R2) and by calculating you have a measured Zs!!

I think you would be hard pressed to convince a H&S investigation that it was necessary to "live" test Zs in a domestic premises and not follow reg 14 of EAWR's. You could argue commercial/industrial may need "live" Zs where operational commitments mean you can't power down circuits, hospitals being a classic case.



But not 100% safe which a "dead" (R1&R2) should be for the trained electrician!!


....... oh, and its nice to be back for a fleeting visit to add some contention to debates

Jesus Christ almighty, you don't understand the basics of why we carry these tests out?

A Zs test and an R1+R2 test are different things entirely. The result almost never equals the calculated value. A Zs test passes a relatively high current through the circuit which will identify any poor connections far better than the low current continuity test.
The Zs test will give you the impedance including all paralell paths so a circuit tested this way may pass when the calculation method fails it.
The Zs test will include all of the terminations in the CU and the protective devices, highlighting any faults which could start one of these CU fires we are hearing so much about.

 

[stevethesparks]

Re: High zs readings low ez readings

The Zs test will give you the impedance including all paralell paths so a circuit tested this way may pass when the calculation method fails it.

Should such a Zs be accepted, hence my earlier reference to conducting a Line Impedance test where no parallel paths are measured.
Some parallel paths may well be temporary.

 

[davesparks]

Re: High zs readings low ez readings

Should such a Zs be accepted, hence my earlier reference to conducting a Line Impedance test where no parallel paths are measured.
Some parallel paths may well be temporary.

Depending on the earthing system it may not be possible to conduct any test without paralell paths affecting it.