Ze, ZS, R1 And r2 ( 2 part question)

[gpz900jim]

Hi. I wonder if anyone could help me. I have a fluke 1651b multifunction tester. If I take a ZS reading using the loop Z1 no trip function on the dial (uses 3 leads on this setting). If I press f3 before i do the test, it also gives you your zE reading as well as your zs (dont know how it does it, it says in the instructions that it does it by calculation) On a minor works certificate that I have. It asks for a Zs reading and an r1/r2 reading. using the 2 readings i am given from my tester. if I was to subtract my zs reading from my Ze reading, is the result an acceptable way of getting my r1/r2 reading.
Now for the nest question. I am thinking about obtaining zs reading from a radial circuit with a neon light in the switch in the circuit.and taking the test from the very end of the circuit, Using the same setting on my tester, which uses 3 leads for the zs reading, Would the fact that there is a neon in that circuit make the meter give me an incorrect zs (and also a ze reading)
thanks for your help

 

[telectrix]

you do not calculate R1+R2 from Zs. they are readings which must be taken first on a dead cct. it is acceptable to calc. Zs form Ze+R1+R2 if you are unable to measure it. don't get confused between R1 and r1, etc. they are entirely different readings. the neon will only give you probs. on insulation testing

 

[antimatter]

Why not do a R1 + R2 reading dead test at the back of the socket therefore discounting the resistance of the neon light.

Enter that in the your Minor Works Certificate along with Insualtion Resistance details and Circuit Protection details and Eathing arragements.

Then all you need is your ZE reading which you took earlier, when you pressed F3 before the test (think it says RE) on the LCD display on your tester.

Check all readings are within accepted tollerances.

 

[gpz900jim]

thanks, but if i take the R1/R2 reading from the switch back to the cu, will i also have to take an R1/R2 from the switch towards the appliance, then add them together for a true R1/R2 value for the circuit??

 

[telectrix]

short out at CU. read R1+R2 at each fitting and at each switch. record highest reading. job done

 

[gpz900jim]

cheers but if you can measure a zE (live test) and add it to an R1/R2 (dead test) to get a zs, Why cant you use a zs (live test)subtracted from a ze (live test), wouldnt that give you your r1/r2 value. I know i must be missing something, there is no way I am disputing the info that i have been given, im just trying to understand why?

 

[telectrix]

to put it simply,one reason, and i think it's the main reason, is that you should not energise any circuit until you have confirmed continuity ( R1+R2). as you have not yet energised the cct., you cannot perform a live test.

 

[gpz900jim]

i see, so its not that the reading would be wrong, its a safety issue?

 

[WayneL]

If I press f3 before i do the test, it also gives you your zE reading as well as your zs (dont know how it does it, it says in the instructions that it does it by calculation)

This isn't possible because Ze is measured with the 'Earthing Conductor' disconnected, where Zs is measured with it connected - so how would the meter allow for this.

If it deducted your measured R1 + R2 (resistance of L and CPC) value from the measured Zs value, it's still not going to give you Ze.

 

[WayneL]

i see, so its not that the reading would be wrong, its a safety issue?

The reading would also be wrong because the R1 + R2 value is the resistance of the Line conductor added to the resistance of the CPC only.

Zs - Ze will give you R1 + R2 + Parallel Paths.......this would give you a lower reading than it actually is.

 

[telectrix]

correct. also, it's regs. to record an accurate, measured value for R1+R2. (not calculated). This reading is the first to be taken on a periodic and compared with previous readings , so as to identify a potential fault. As I think I have mentioned before, never get confused with r1,r2,rn. these lower case letters denote the end to end readings for a ring circuit.

 

[gpz900jim]

does ze mean the earth loop impedance of the suppliers electrode, or does it mean external earth loop impedance, which would include all parallel paths?

 

[J@mes]

It shouldn't include any parallel paths as these cannot be relied upon. Ze should be measured with the main earth terminal disconnected so you ONLY get the fault path from the TX back to the earth as supplied by the DNO.

 

[gpz900jim]

thanks for that. im only a beginner and i am very grateful to all of the help that everyone on this site offers.

 

[Jimmy Boy]

Waynes bang on the money with his posts. Parallel paths are a danger, when doing a Ze this is not only to measure the external impedance to check if it falls within the regs, but also to check you actually do have an Earth connection, if not disconnected from the board you will get a reading through all or any parallel paths, water, gas and any other extraneous conductive parts that may be bonded to MET.

ATB Steve