What's the difference between Zt, Zs and (R1+R2)

[Spark123]

You mean the action if the tennant declines the remedial action?

 

[ban-all-sheds]

or is Part P "an ASS"!!!!

It's not Part P that's the ass....

 

[Click-Sure]

Question one: Mixed up on what R2, Ze, R1+R2, Rn, EFLI are?

Question 2: Whens your ELECSA assesment booked for?

 

[ericmark]

This do nothing and it is more dangerous comes up many times. But we have to also protect our selves. If you think anyone will go to court as say he said it was dangerous but I asked him to do it anyway then your living in cloud cuckoo land.
The problem is there is always a way around the problem and if some one is injured some one with hind sight some one will point it out. Including using a transformer and 50 volt lighting! just one way!
The point given is often well we are not allowed to just switch it off. Then one sees where a RCD has been tested or a R1 + R2 reading is entered ups!! Then who turned it back on?
If you tell some one sorry I am not permitted to turn it back on with these faults. What you do when I leave is up to you. One knows they may well turn it back on when you leave but they are also well aware the installation is faulty. But turn it back on and say "I should not really turn that back on" and the customer does not perceive the same amount of danger.
And my grand parents didn't have electric lights and they did not die because of no light! They has candles and gas lights. Today we have standard lamps and table lamps and to claim there is a great hard ship because the ceiling mounted lights don't work is a load of rubbish.
We all know we can fit wall lights using FCU's and we all know wireless light switches are available to control them from a convenient location. OK maybe there is an issue that if someone trips RCD on sockets you lose lights. Well even that holds little water there are emergency type lights if you are really worried about that.

So lets be honest only reason why you leave lights without an earth is because you want to.

In your own home then again the only reason is that you want to. There is always a way to correct it.

However as to if there is any real danger without an earth or only a perceived danger is another question. Here where we can hand on heart say there is no way the occupier is going to ever fit any thing other than class II fittings I can't really see a danger. Remembering this also means non metallic screws in switch plates. The only place where this could be true is ones own home.

One problem would arise if one wanted to sell it. The same applies to other things in ones own home. Although I do have RCD's on all circuits in my home I suppose following the 17th Edition I could get away with not fitting RCD's to protect cables buried less than the 50mm in my own home. 522.6.7 will allow me because my home in under the supervision of a skilled person not to use RCD's on the lights etc. But what if I want to sell or die? (Not that I would WANT to do that!) Do you really want to leave your loved ones not only sorrowful for their loss but also got to rewire the house before they can sell it?

We all know what we should do is there really any need to debate it on here?

 

[duncanhead]

Question one: Mixed up on what R2, Ze, R1+R2, Rn, EFLI are?

Question 2: Whens your ELECSA assesment booked for?

I know very well R2, Ze, R1+R2, Rn (think that it's actually rn) , not sure wot EFLI is though - please enlighten me!!

Q2: my ELECSA assesement is not booked yet, need one more exam... and perhaps some more experience... hmmmm...

 

[jockspark]

sorry mate but you are nowhere near ready for your assessment
EFLI (earth fault loop impedance)

 

[duncanhead]

sorry mate but you are nowhere near ready for your assessment
EFLI (earth fault loop impedance)

Ok! point taken, I just know it as the fault loop impedance, either high (25 Amps) or no trip 15mA type test or Zs, but I give that to u, the latest forms do state "earth fault loop impedance" to be very precise, but of course a fault loop involves R2 and so the cpc and thus earth, I'm just used to checking Zs (and my Megger setting "loop test")

 

[jockspark]

hi duncan 2 books i would recommend to you
inspection,testing and certification ( brian scadden )
practical guide to inspection,testing and certification
of electrical installations ( christopher kitcher )

and if you dont have them yet bs 7671/ the on site-guide and guidance note 3
try and get a bit more practical experience before you book your assessment
speak to elecsa they may be able to help
goodluck

 

[duncanhead]

This do nothing and it is more dangerous comes up many times. But we have to also protect our selves. If you think anyone will go to court as say he said it was dangerous but I asked him to do it anyway then your living in cloud cuckoo land.
The problem is there is always a way around the problem and if some one is injured some one with hind sight some one will point it out. Including using a transformer and 50 volt lighting! just one way!
The point given is often well we are not allowed to just switch it off. Then one sees where a RCD has been tested or a R1 + R2 reading is entered ups!! Then who turned it back on?
If you tell some one sorry I am not permitted to turn it back on with these faults. What you do when I leave is up to you. One knows they may well turn it back on when you leave but they are also well aware the installation is faulty. But turn it back on and say "I should not really turn that back on" and the customer does not perceive the same amount of danger.
And my grand parents didn't have electric lights and they did not die because of no light! They has candles and gas lights. Today we have standard lamps and table lamps and to claim there is a great hard ship because the ceiling mounted lights don't work is a load of rubbish.
We all know we can fit wall lights using FCU's and we all know wireless light switches are available to control them from a convenient location. OK maybe there is an issue that if someone trips RCD on sockets you lose lights. Well even that holds little water there are emergency type lights if you are really worried about that.

So lets be honest only reason why you leave lights without an earth is because you want to.

In your own home then again the only reason is that you want to. There is always a way to correct it.

However as to if there is any real danger without an earth or only a perceived danger is another question. Here where we can hand on heart say there is no way the occupier is going to ever fit any thing other than class II fittings I can't really see a danger. Remembering this also means non metallic screws in switch plates. The only place where this could be true is ones own home.

One problem would arise if one wanted to sell it. The same applies to other things in ones own home. Although I do have RCD's on all circuits in my home I suppose following the 17th Edition I could get away with not fitting RCD's to protect cables buried less than the 50mm in my own home. 522.6.7 will allow me because my home in under the supervision of a skilled person not to use RCD's on the lights etc. But what if I want to sell or die? (Not that I would WANT to do that!) Do you really want to leave your loved ones not only sorrowful for their loss but also got to rewire the house before they can sell it?

We all know what we should do is there really any need to debate it on here?

Ok, so are you stating that because that I know that there is a departure but (I) do not correct this and if there is a future problem then I am legally responsible? Should I then get a solicitor to send a letter to my family stating that the wiring does not meet the regs and that I can correct it if they pay me a sum of money? (and if they don't and an accident occurs then I'm indemnified) as they haven't responded/paid, I could easily set up a "contract" for a member of my family stating that the "wiring" does not meet current standards, that I'm financially unable to remidy this but that they will not sue me for any "issue/accident or otherwise" , I could do this as I technically know of the issues but do I really need to do this legally, I'm serious... (it's about mitagation and disclosure etc) As I stated it's not because I don't want to, it's for financial reasons, someone send me £3000 and it'll be "fixed " in 10 days, but the DWP won't "stump" up this cash for this, crisis loan or not!!! but I am prepared to make a "case" from the outcome of this Forum

 

[duncanhead]

hi duncan 2 books i would recommend to you
inspection,testing and certification ( brian scadden )
practical guide to inspection,testing and certification
of electrical installations ( christopher kitcher )

and if you dont have them yet bs 7671/ the on site-guide and guidance note 3
try and get a bit more practical experience before you book your assessment
speak to elecsa they may be able to help
goodluck

thx for the help!

 

[ericmark]

Ok, so are you stating that because that I know that there is a departure but (I) do not correct this and if there is a future problem then I am legally responsible? Should I then get a solicitor to send a letter to my family stating that the wiring does not meet the regs and that I can correct it if they pay me a sum of money? (and if they don't and an accident occurs then I'm indemnified) as they haven't responded/paid, I could easily set up a "contract" for a member of my family stating that the "wiring" does not meet current standards, that I'm financially unable to remidy this but that they will not sue me for any "issue/accident or otherwise" , I could do this as I technically know of the issues but do I really need to do this legally, I'm serious... (it's about mitagation and disclosure etc) As I stated it's not because I don't want to, it's for financial reasons, someone send me £3000 and it'll be "fixed " in 10 days, but the DWP won't "stump" up this cash for this, crisis loan or not!!! but I am prepared to make a "case" from the outcome of this Forum

I apologise I was out of order in the way I put that. Sorry. I was having a bad day. I am sure when funds allow you will correct and as I did state done correctly there is not Danger.

Problem is of course there is always another way around a problem. And what I was trying to say is you can't hand on heart say "I can't afford to follow regulations" there is a method which can be followed that will comply which is affordable even if that is using standard lamps.

However it is undesirable. And I will admit I would not want to remove ceiling lighting myself.

And in real terms it is work postponed to a later date. I am sure at some point you intend to re-dress the problem. And you don't intend to just forget about it.

I also have work I planed to do back when my extension was built. I want to replace my old Wylex boards for boards able to take din rail mounted MCB's or RCBO's and redress the problem I have where too many PC's in the house can trip the RCD's on the main incoming supply.

That has been waiting to be done for last 10 years and some day it will be done.

But to present the work to an assessor and to try to claim you tried to persuade yourself to have more work done but you were unable to persuade yourself seems to have a flaw? However to say you have completed stage 1 and stage 2 will be to do the lighting seems a better way to present the work?

I did a very poor job of presenting my thoughts on the subject so maybe I am the wrong person to say this. I hope this time I have said it in a better manor and you can see I am not criticising what you have done but I am criticising the way you are presenting it.

Again my apologies for my first post on re-reading I can see it was out of order. I was not thinking straight. I hope you will see it is not what one says but how ones says it that matters. And I had got it wrong Sorry.

 

[Spark123]

sorry mate but you are nowhere near ready for your assessment
EFLI (earth fault loop impedance)

Ok! point taken, I just know it as the fault loop impedance, either high (25 Amps) or no trip 15mA type test or Zs, but I give that to u, the latest forms do state "earth fault loop impedance" to be very precise, but of course a fault loop involves R2 and so the cpc and thus earth, I'm just used to checking Zs (and my Megger setting "loop test")

Nope, the 25A and 15mA is the current which the MFT will deliver in testing for the Earth Fault Loop Impedance, the latter being the non-RCD Trip one which is a little bit less acurate than the 25A one.
It is important to know what the figures which your meter spits out at you actually mean and what to do with them.
It is all fine filling in an EIC but I can write any figures I like on the form, unless I know that I am not to exceed the maximum earth fault loop impedance for a given protective device to disconnect a certain time then I wouldn't be competent and hence would be putting my head on the block for filling it in, nor for the design or construction if I was responsible for that.
Earth isn't usually part of a fault path unless you are on a TT system, or you are getting a shock!

 

[ban-all-sheds]

. . . . .

Anyway, back to the plot......

What's the difference between Zt, Zs and (R1+R2), I thought that Zs was the loop impedance, Zt ? and either R1 or R2 can be measured directly or derived from the difference between Zs and Ze, or am I totally confused?!

According to this:



ZT is the impedance of the source. The same list of abbreviations does not include Ze, so maybe it's the same? The list, BTW, is from CENELEC report R064-003, so maybe ZT is the harmonised symbol?

It's not in the list on pp 35-36 of the 17th regs though.

But then the same Design Guide list talks about ZQ, which is the impedance upstream of the source, and says that ZS = ZQ + ZT.

Which makes the definition of ZQ hard to grasp, as what I would have said was upstream of the source was the 11kV supply, except that's the other side of the transformer...

Then again I've seen ZT defined as the impedance of the source not including the cable downstream of it, i.e. just the transformer windings. Maybe where the T comes from?

Whitfield helpfully ( ) defines ZT as the tabulated EFLI values (e.g. those in Table 41.3, 41.4 etc), and that its relationship to ZS is that ZT is adjusted by the ratio of the actual supply voltage to the 230V nominal voltage that the tabulated values assume, i.e. ZS becomes the actual EFLI value you need to achieve for safety.

ZS = ZT x . . U . .
. . . . . . . . . . . . . . U0

Except of course BS 7671 defines U as the nominal line-line voltage, not the actual line-earth voltage.

And this search: http://www.google.co.uk/search?sour...GGLL_en-GBGB302GB302&q=zt+site:www.theiet.org doesn't help - no consistency of answers there.


Maybe I'll ask Paul Cook...