Zs testing......which camp are you in?

[Dan007]

I've been reading a book by a guy called Anthony Hinsley where he states that when performing a Zs test you should disconnect the equipotential bonding conductors connecting the MET to the incoming gas and water. The reasons behind this being that by disconnecting you:

1. Get a realistic value for Zs

2. Reduce external parallel paths

3. Definitively test the earthing provisions within the circuit under test and

4. Conform to H&S by making the test safer.

Now this all makes perfect sense to me but so does the stance of the IET with regard to leaving them connected (as stated in GN3 the OSG ect and by my old college tutor and most practicing sparks I know) as in normal service if a fault occurs the conductors would be in place.

I'm interested to know what school of thought is the most popular out there?

 

[Andy™]

Zs includes parallel paths... which is why its almost always lower than Ze+R1R2

and id love to see the risk assessment for energising an installation without earthing being in place....

 

[steptoe]

Im with Andy on this,

Exactly my thoughts,

BTW, I usually do calcs on R1 F2f now anyway due to dodgy results on low trip testing.

 

[NozSpark]

Same as the guys above...

I find it hard to beleive that someone is giving advice that you can carry out live tests with the MEB's disconnected

 

[Dan007]

I'm with you guys on this but he goes on to say

"if you carry out the test with the main equipotential bonding conductors connected, the measurement of Zs becomes worthless and the risk of shock induced into another electrical system in close proximity (such as flats, terraced houses and different installations within hospitals and industrial buildings) is in-quantifiable, and in my opinion unsafe, uncontrolled and completely out of the hands of the inspector and definately in breach of H&S."

Strong words and food for thought no?

 

[Andy™]

i think you need to get a different book

Zs also does one very important thing - if you dont put the earth connection back properly after Ze or R1R2, then you will know about it. if you calculate it, then youve missed your chance

 

[Dan007]

To be fair it's a really good book apart from this bit which is why I'm questioning his methods and trying to get more opinions. With regard to not connecting them back properly he says "if a proper system of reporting completion of the test has been carried out, verification and final visual inspection as detailed in the permit to work should highlight and double check that they have been reconnected." but I think I'll stick with my GN3 for now. Thanks for your opinion

 

[Voltimax]

That's not the plonker who posts on the IET forum and gets ridiculed all the time by the heavy hitters there is it?

I recall someone on there who's published a book and apparently everything printed in it is rubbish. I can't comment as I haven't read the book, but the phrase don't believe everything you read springs to mind.

 

[Nicky Tesla]

Im with Andy on this,Exactly my thoughts,

BTW, I usually do calcs on R1 F2f now anyway due to dodgy results on low trip testing.

I do the same now.........The results are usually a mile inside the max levels anyway, but why are they so different?

 

[PC Electrics]

You sure you are not confusing measurement of Ze and Zs. Ze would be taken with the installation de-energised and the MEBs disconnected, whilst Zs would be taken on a live install (eg at a socket) with the MEBs and all earthing connected.

Could it be a misprint in the book? Zs for Ze?

 

[Dan007]

No definately Zs in all examples, ring final circuits, lighting and three phase motor circuit. And he goes as far as a whole page of explanation behind his reasons which I've tried to breifly explain in my earlier posts. It's the whole reason I bring it up because he is so confident in his explanation....he's even got letter after his name (MA MIEE)so he must know more than I do!!!

 

[Manator]

From his explanation of reasons it is very apparent that he has never done any testing in a hospital, from the main earthing terminal bonding is taken to all patient areas and connected to earth reference bars(ERB), from this all the equipment within the room are cross bonded. During testing these are separately tested for continuity, and tested together back to the MET. All Zs testing is done with everything connected, and is a live test.

So I would definitely agree with the other posters, and carry out your testing to the described methods and not to anyone who writes a book based on his personal interpretations.

 

[Dan007]

"Testing electrical installations a practical guide for electricians"

Look that title up on amazon and read the reviews. One guy goes into one about how right this book is and seems to take it quite personally when people challenge the author. So I thought I'd read it myself. I nearly thought I was doing it wrong! Glad you guys have confirmed what I have always known....... Stupid Anthony Hinsley

 

[steptoe]

I havent even read all this thread,

simply send this ******* round to me and I'll try and educate him.

this sort of stuff should be illegal

 

[philbas]

I did look it up. read the excerpts, and looked for a brick wall to bang my head against

 

[PC Electrics]

Give us the ISBN - it makes it so much easier to find the right book (it'll be printed on the back cover probably)

Letters after ones name is no guarantee of knowledge or competence. And that's from someone with a BSC (Hons) who used to be a ChEng, MIMechE.

When I was in the automotive field, one engineer with a First genuinely believed the rear wheels of a car were on 'castors' so they could follow the fronts, shopping trolley like. Fortunately she was designing trim.

 

[NozSpark]

I think you should get a copy of "Alan Lynch's Part P Doctor",,, now that is a good book

 

[PC Electrics]

Or better still, give us a link into the amazon page, save us all looking individually.

 

[philbas]

Well I have had to much to drink to work out what thy stand for but more letters P.R.I.C.K, suggestions on a post card

 

[Dan007]

http://www.amazon.co.uk/Testing-Electrical-Installations-practical-electricians/dp/2952413835/ref=sr_1_1?s=books&ie=UTF8&qid=1312751659&sr=1-1

Or ISBN 2-9524138-3-5