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Topic Title: Ze, Zs, R1, R2
Topic Summary: Please explain
Created On: 07 March 2005 07:54 PM
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 07 March 2005 07:54 PM
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deleted_Wheelie

Posts: 28
Joined: 07 March 2005

Can someone please take 5 minutes out to explain what these are. I have worked in electrics in a factory for years (mainly robotics and panel building) and am considering going to self-employed domestic electrics. I have a good understanding of the basics but need to be up to speed on the testing side of things. I do intend to get on some testing courses but it would greatly help if I could start learning the testing and inspection now.

Thanks in advance
 07 March 2005 10:24 PM
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pm70511

Posts: 118
Joined: 07 March 2005

Wheelie,

Ze = is the external loop impeadance (from the suppler side of the consumer unit back to the transformer)
Zs = is the system loop impeacence (ie the circuirt from the cunsumer unit out to the sockets / lighting etc)

R1 = resistance of phase conductor ie Live.

R2 = resistance of cpc ie earth.

Cheers Paul.

-------------------------
Kind Regards

PM70511

Why do kamikaze pilots ware crash helmets?????
How do you know the fridge light goes off when the door is closed?????
 08 March 2005 11:19 AM
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deleted_nonsparky

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 08 March 2005 11:30 AM
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mapj1

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But before rushing out to Amazon.com, read the inspection/testing sections here for free.

its a good refresher for those with fading memories, and OK as a primer for those who already understand the basics..
regards M.
http://www.tlc-direct.co.uk/Book/1.1.htm

-------------------------
regards Mike

Edited: 08 March 2005 at 11:33 AM by mapj1
 08 March 2005 12:00 PM
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deleted_1_khales

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quote:

Originally posted by: nonsparky
Buy copies of these:

http://www.amazon.co.uk/exec/obidos/ASIN/0863413749

http://www.amazon.co.uk/exec/obidos/ASIN/0953788539

http://www.amazon.co.uk/exec/obidos/ASIN/0852962371

Or, even better (from my point of view), use these Amazon links (and then I get my Amazon Associate's referral fee! Every little bit helps!)

http://www.amazon.co.uk/exec/obidos/ASIN/0863413749

http://www.amazon.co.uk/exec/obidos/ASIN/0953788539

http://www.amazon.co.uk/exec/obidos/ASIN/0852962371

(Hmm. Is that against Forum rules?)

-------------------------
khales

Edited: 08 March 2005 at 12:04 PM by deleted_1_khales
 09 March 2005 03:06 PM
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deleted_Wheelie

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Thanks all for your help.

I intend to buy the books but can someone tell me what special equipment I need to buy over and above a multimeter and insulation resistance tester? Which do I use for the tests to determine the above figures and how?
 09 March 2005 04:03 PM
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mapj1

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To measure R1 and R2 and the like, you need a low impedance ohms range, ideally capable of measuring below 0.1 ohms.
to measure Ze you need an 'earth loop' type tester, but before you rush out realise that the current used for the test varies, and many will trip an RCD protected circuit, amking reading impossible without testing before the RCD (or bridging it out) Some can also be used to test earth spikes.
As I said, read the TLC website, the pictures and descriptions are well worth it.
regards M.

-------------------------
regards Mike
 10 March 2005 10:47 AM
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deleted_nonsparky

Posts: 1962
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quote:

Originally posted by: khalesOr, even better (from my point of view), use these Amazon links (and then I get my Amazon Associate's referral fee! Every little bit helps!)


Surely what you meant to say was "Even better, join the IEE and get 20% off the price of the books"....

-------------------------

I don't suffer from stress - I'm a carrier...

 10 March 2005 06:18 PM
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deleted_Wheelie

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Could anyone show me a sample of the Electrical Installation Certificate form FILLED IN? I have downloaded the forms but I still have a few questions. For example, I'd be interested as to what fields are filled in and how for, say, a Consumer Unit change. I'd also like to see how a minor works form is done for a socket change or lightswitch change. If any of you have a scanner (and the time after all that paperwork!) I think it would help me and lots of others who are thinking of a career in electrics but are put off by the forms.

Mapj1, can you recommend a good earth loop tester? Thanks for the tip about the TLC site, I have square eyes!
 11 March 2005 05:41 PM
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deleted_nonsparky

Posts: 1962
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quote:

Originally posted by: Wheelie
Could anyone show me a sample of the Electrical Installation Certificate form FILLED IN? I have downloaded the forms but I still have a few questions. For example, I'd be interested as to what fields are filled in and how for, say, a Consumer Unit change. I'd also like to see how a minor works form is done for a socket change or lightswitch change. If any of you have a scanner (and the time after all that paperwork!) I think it would help me and lots of others who are thinking of a career in electrics but are put off by the forms.

The OSG has examples.

quote:

Mapj1, can you recommend a good earth loop tester? Thanks for the tip about the TLC site, I have square eyes!

Fluke, Robin, Megger, Beha Unitest, Seaward....

But BTW - you need more than just an earth-loop tester.....

-------------------------

I don't suffer from stress - I'm a carrier...

 12 March 2005 08:57 AM
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deleted_Wheelie

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Is the on-site-guide up to date as it was printed in 2004, before the current change in regulations (competent person self-certifyiing etc). Has this changed the paperwork at all?
 13 March 2005 12:29 AM
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deleted_nonsparky

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No.

The "new regulations" are Building Regulations, not Wiring Regulations. They have nothing to do with wiring regs, and EICs etc have nothing to do with certification of compliance with Building Regs. You do not need to be able to self-certify compliance with Building Regs to write installation certificates. Whatever competence you had to do EICs on 31/12/04 you still have.

-------------------------

I don't suffer from stress - I'm a carrier...

 13 March 2005 04:59 PM
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deleted_Wheelie

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Thanks for clearing that up. So would I be OK to self certify my work after 20 years as an electrician and several exams the most recent of which was 6 years ago (C&G 236)?
Is there really any need to join a body like the NICEIC etc? Most electricians I speak to are not registering their jobs and are just self-certifying to BS7671. It appears membership of a body would cost me hundreds of pounds a year to have 1 job of my choice checked. So much for consumer confidence (or am I missing something?).

Sorry if this question has been done to death but it is the most interesting for someone in my position.
 13 March 2005 06:44 PM
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stevendoust

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quote:

Originally posted by: pm70511
Wheelie,

Ze = is the external loop impeadance (from the suppler side of the consumer unit back to the transformer)
Zs = is the system loop impeacence (ie the circuirt from the cunsumer unit out to the sockets / lighting etc)

R1 = resistance of phase conductor ie Live.

R2 = resistance of cpc ie earth.

Cheers Paul.



Just a minor correction, the Zs of an Electrical Installation is the impedance of the entire system, that is from transformer to socket outlet or final circuit. What pm770511 describes above is the R1 + R2 of the circuit.
Sorry too be paicky but it is important to get it right.

Steve Doust
 14 March 2005 08:07 AM
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deleted_nonsparky

Posts: 1962
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quote:

Originally posted by: Wheelie
Thanks for clearing that up. So would I be OK to self certify my work after 20 years as an electrician and several exams the most recent of which was 6 years ago (C&G 236)?

Your use of the phrase "self-certify" worries me - apologies if I'm wrong, but I don't think you've got it.

You are just as qualified as you ever were to write EICs etc.

THIS IS NOT THE SAME AS BEING ABLE TO SELF-CERTIFY COMPLIANCE WITH PART P OF THE BUILDING REGULATIONS

quote:

Is there really any need to join a body like the NICEIC etc?

If you wish to be able to self-certify compliance with the Building Regs, then yes.

quote:

Most electricians I speak to are not registering their jobs and are just self-certifying to BS7671.

That is not what the law requires. Unless the work that they are doing appears on the list of minor work that is not controlled, then they, or their customers, are breaking the law.

quote:

It appears membership of a body would cost me hundreds of pounds a year to have 1 job of my choice checked. So much for consumer confidence (or am I missing something?).

You need to read more about Part P here, and in other fora such as Screwfix and DIYnot. In a nutshell - you are to be assimilated or put out of business.

-------------------------

I don't suffer from stress - I'm a carrier...



Edited: 14 March 2005 at 08:08 AM by deleted_nonsparky
 15 March 2005 06:35 PM
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deleted_Wheelie

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No wonder you say Shpx Cneg C then ;-)
 15 March 2005 10:09 PM
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deleted_nonsparky

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-------------------------

I don't suffer from stress - I'm a carrier...

 19 March 2005 04:34 PM
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deleted_Wheelie

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OK, think I'm getting there now, trying to imagine filling in an electrical installation certificate and seeing where I would fall down. A few questions again:
1. Prospective fault current is stumping me a bit. How do I calculate this without a dedicated meter? The elec installation certificate states 'by enquiry or measurement'
2. For external loop impedance, is a figure of 0.3 ohms realistic?
3. Are there any guidelines as to what the maximum Ze should be?
4. How would I determine maximum demand (load) in amps per phase?
5. If I measure insulation resistance and it shows as open circuit, would I record this as such or do I specify a 'greater than' figure?
6. What are the upper limits for RCD diconnection time?
7. For all ring circuits would I use Zs = ZE + (0.25 R1) + (0.25 R2)?
8. " Method of protection against indirect contact" - Is this just filled in as "RCD"? If so, what do you put if there is not one fitted?

Again, thanks for helping out if you take the time to answer these. My books are ordered and on their way. Just need to find some good Inspection and Testing courses now.

Finally, any recommendations on test equipment would be greatly appreciated;
RCD tester
Earth fault loop tester
I'll be buying these very soon.

Edited: 20 March 2005 at 08:36 PM by deleted_Wheelie
 21 March 2005 09:58 AM
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mapj1

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1) When you do fault current by calculation, rsather than by using the ELFI meter, you measure the resitsnces of the circuits at the board with L-E shorted at the load, and add to that wirig resistance, the external resistance of the supply, which is supposed to be guaranteed by the DNO. (and they should be able to tell you, but often can't.)
However, in reality, in the way that "A Smith and Wesson beats 4 Aces" -with apologies to cowboy film fans everywhere, a measurement beats 4 'phone calls . Whne not measured it is normal to assume 0.8 ohm max, but it CAN be higher.
2) For TNC or TN-s 0.3 ohms sounds quite reasonable. Nearer the substation might be less.
3) yes, 0.3 ohms and 0.8 ohms are the two numbers that come to mind. **
4) either from the main fuse, or the sum of the subcircuits with diversity, whichever is lower **
5) greater than and the number that is the upper bound of your instrument scale. **
6) Depends on spec.
7) Are R1 and R2 'round loop' or feed to far point in this example? remember what we want is a fault current as if there where a short at the far point of the ring.
8) The fuse/breaker and the low ELFI can be the some means of disconnection (unless the power goes to supply stuff outside.)
regards M.

** indicates that not everyone does it this way.- there is more than one right answer !

-------------------------
regards Mike
 22 March 2005 08:40 PM
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deleted_Wheelie

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Thanks Mapj1 for your detailed answer

2. What about TNCS? Is 0.3 still about right?
7. Don't understand what you're saying there. Can you expand on that?
8. So would I put 'RCD' if there is one or breaker/fuse if not?
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