Conduit as earth????

[mickytuff]

Hi all done some testing work at a hospital and the orignal wiring was done in metal conduit, now the zs figures tested all good, my question is can u calculate the r1 and r2 figure when their isnt an earth cable as such???

 

[Edd]

Good question,, as for r1 thats your line conductor, and r2 being your earth in this case the conduit. in this set up I use a wander lead and zero my meter with this long lead. then go around pokeing it onto every acessory's earth the highest reading I take as my r2 reading for the test cert

 

[Guest123]

You cant calculate R1+R2 from Zs anyway, even if a seperate cable was being used as CPC due to all parallel paths included when live testing Zs.

 

[nickblake]

biggest probelm is if the conduit is broken you should really do a Zs at every point to confirm polarity and earth continuity ,what you should do is an r2 test instead of the r1r2 but note it on the test certs as conduit used as earth

 

[Edd]

LOL,, should have read the post better!! didnt see the calculate bit thought he was asking how to take the reading.. my bad..

 

[mickytuff]

So on the cert in the earth continuity box what would you put l/l n/n and then????? I agree doing the r2 method to confirm the earth, which is also confirmed by doing the zs test but do i leave the box blank or put n/a due to the nature of the wiring system used????, oh and thanku all for your ideas, all gratefully recieved, shud of said that 1st realy

 

[Edd]

I put con or mech in the CPC box for ring mains, and would put a - in the r1-r2 box and put my r2 reading in the r2 box

 

[Guest123]

I'm confused even further now.

Are you referring to the section for the cable sizes i.e 2.5/1.5 for a normal RFC??? Where conduit is used as the CPC, under the CPC size i enter 'K'.

For the measurements, L-L (r1), & N-N (rN) are as normal, for E-E (r2), again I put 'K' in the box.

 

[Edd]

thats the way I read it lenny,, but i have to say can you tell me about the 'K' ive always put mech or con in them places..

 

[telectrix]

thats the way I read it lenny,, but i have to say can you tell me about the 'K' ive always put mech or con in them places..

Konduit???

 

[mickytuff]

When testing i use the amtech software and you can select the earth as conduit, you enter in the size of the conduit and it gives you a equivelant figure as a c.s.a of 80mm for 20mm conduit, meaning the conduit is acting like the size of a 80mm cable i presume, strange i know, but this figure cant be accurate, as the condiut could be 1m long or 30m in length, so this isnt realy accurate, the column i was reffering to was the ring final contuity part, what i've just said is the column your referring to, i.e the cable size part.

 

[mickytuff]

I understand what your saying lenny, you put k in the e-e box and enter your r2 reading in the r2 box, as you cant calculate the r1/r2 conventially? Correct?

 

[mickytuff]

So you ready for my next question???

 

[nickblake]

braced and waiting lol

 

[mickytuff]

Ok nickblake here we go...............while testing with a megger multi, if you chose to test on notrip on your loop test, why do U have to connect all three leads, if you connect just line and earth it wont produce a reading and just say trp on the display, yet when you deselect no trip it tests fine with just two leads connected, so there you go, any body else had same problem???????????

 

[MarkieSparkie]

Ok nickblake here we go...............while testing with a megger multi, if you chose to test on notrip on your loop test, why do U have to connect all three leads, if you connect just line and earth it wont produce a reading and just say trp on the display, yet when you deselect no trip it tests fine with just two leads connected, so there you go, any body else had same problem???????????

In "No-trip" mode the Megger MFT electronics requires 3 wire L, N and E connections for power and reference so that the sophisticated method of noise cancellation that the Megger uses can resolve the impedance from the low level "No-trip" current pulses, even in an electrically noisy environment. It is because of this multiple current pulse and noise cancellation technique that the Megger gets unfair criticism from users of other MFTs (Fluke particularly) for it's apparently slow "No-trip" test, however, Megger users get the last laugh because they very rarely have their test inhibited by a noise error.