r1/r2 and ze dont measure up?

[Jimmy Boy]

yes measured zs with plug adaptor, what reading would you be looking for steve? also why will ze=r1+r2 never really give an accurate reading? thanks for all your help im quite new to the testing side of things and classroom learning and on the job situations are a bit different!!

Your R1+R2 is a 'Dead test' isn't it, the Zs is a 'Live' test isn't it, so because it's a Live test the cpc of the circuit is connected to earth and everything bonded to earth so you will have parallel earth paths.

 

[Jimmy Boy]

I have just today had this
tested ZE live side of RCD then load side and there was a differance of .40 ohms
this would explain it

Sorry if I have wrong end of stick it's late. A Ze test is conducted with the supply to the installation OFF and preferably locked off the main Earth is disconnected from the CU and measurement is taken between Line a E. After this you reconnect the Earth and carry out your PEFC and PSSC test to gain your PFC for the cert, so why would you have the load side energised ? and measured through an RCD ? Not looking for an argument just to clarify your method.

ATB Steve

 

[Sintra]

I think beaver was testing each side of the RCD to check for a rise in impedance although this would not be a Ze test.

 

[Jimmy Boy]

Sorry mate I don't understand ? He distinctly said he was testing for Ze ?.
Can you explain the test he was doing as I am eager to learn

 

[Sintra]

I have had instances in the past were my figures were way out as in the original post and couldn't find an obvious answer apart from the additional components involved between continuity testing and earth loop testing. ie an MCB or RCD or both. If you have an MCB etc with a high resistance then your Zs figure will be high so a way to check out a MCB or RCD is to conduct a loop test at both the supply and load sides of the device. This is the reason that i would always test Zs on all circuits as this is the only test that verifies the complete circuit including MCB's, RCD's etc.

 

[malcolmsanford]

ive just tested a 16a radial socket circuit. r1+r2 was 0.14 ze was 0.2 but measured zs was 0.74. am i right in thinking this is to high? why would i get this figure?

Was this a PIR ? or a new installation. If it was an old installation you may find that you will need to putin/remove the tester plug a few times to clean the contacts as sometimes an old socket outlet can give you odd results.

Also certain type of cheap socket outlets can give you false results as the contacts are made of inferior material. Try pluging something in a few times to clean the contacts then retest. You normally find that a live Zs would be lower than a calcualted one so your results are a suprise.