R1 + R2 expected readings

[cireland]

Previously I’d do dead and live testing and I’d be able to check check the r1 r2 results by the zs readings

Surely a bad connection is going to make BOTH readings off.
How does live testing confirm anything is ok?

 

[Lt1990]

For EICR purposes, the two things that come to mind are how close the calculated Zs is to the limit for the device, and a sense of how big the property you are in is and whether a reading seems plausible. The more you do the easier that gets.
e.g. if you're re in 2 up 2 down and you get 1.5 ohms for an immersion heater circuit then a bit of head scratching is due.

The other thing you can do is try RN+R2 or use a wander lead to obtain a 2nd frame of reference, and whether it's R1, R2 or both that have a loose connection.

I'm assuming that you are allowed to do Ze, Zs@DB and RCD tests, and your company only prohibits live Zs readings?

Yea I generat know what I’m looking at what seems high and things but I just wanted something to work towards incase I was been slightly generous and over cautious chasing faults that didn’t really need further investigation.

And yea so we do ze zsdb And rcd tests
It’s literally just only zs readings that we can’t do

 

[Lt1990]

This is so basic for someone qualified. Whether dead or live testing, you should know the methods of carrying them out (and working them out) without thinking.

I do know the methods for carrying them and things,
I was just asking to know so I knew if I was over cautious or to generous when it came to the readings

 

[Lt1990]

This is a 'modern' take on Zs testing that you don't do it live except for socket outlets where there is no risk of exposed live parts but as @timhoward asks do you carry out Ze and rcd tests.

Yea we carry out ze and rcd tests
It’s just the zs we don’t carry out

 

[Vortigern]

You are either going to be carrying Zs on lights or sockets principally. Spurs come into it as well. I always do live tests at sockets, spurs and lights. I use the lightmate by Kewtech for Zs test. On courses it has been put to me this is a Lim, as you have to go up a ladder and H&S forbid this in many scenarios. I just get on with the job and test it all. When I put the Zs reading for each circuit I like to be sure I did actually read it with my MFT, I can't imagine any other way to operate. Maybe I am missing something, but I don't think so. Convince me! I mean how do you fill in the forms? Yes calculation, but I am not convinced that is kosher. For instance you can find that there are big variances between R1/R2 + Ze calculation and Zs measured with an MFT.

 

[westward10]

Yea we carry out ze and rcd tests
It’s just the zs we don’t carry out

Have you ever asked why seems like someone has carried out a risk assessment and deemed it is not safe.

 

[westward10]

You are either going to be carrying Zs on lights or sockets principally. Spurs come into it as well. I always do live tests at sockets, spurs and lights. I use the lightmate by Kewtech for Zs test. On courses it has been put to me this is a Lim, as you have to go up a ladder and H&S forbid this in many scenarios. I just get on with the job and test it all. When I put the Zs reading for each circuit I like to be sure I did actually read it with my MFT, I can't imagine any other way to operate. Maybe I am missing something, but I don't think so. Convince me! I mean how do you fill in the forms? Yes calculation, but I am not convinced that is kosher. For instance you can find that there are big variances between R1/R2 + Ze calculation and Zs measured with an MFT.

@Lt1990 is only carrying out works in the way as suggested by his company.

 

[cireland]

The place I work also tells us we are NOT to work live.
Dunno how the hell we're supposed to complete EICRs.

 

[Lt1990]

Have you ever asked why seems like someone has carried out a risk assessment and deemed it is not safe.

Where I previously worked we carried out full tests but I’ve only recently started for this place and from what I can gather it’s literally just down to them not wanting us to work live.
They are health and safety mad

 

[Lt1990]

You are either going to be carrying Zs on lights or sockets principally. Spurs come into it as well. I always do live tests at sockets, spurs and lights. I use the lightmate by Kewtech for Zs test. On courses it has been put to me this is a Lim, as you have to go up a ladder and H&S forbid this in many scenarios. I just get on with the job and test it all. When I put the Zs reading for each circuit I like to be sure I did actually read it with my MFT, I can't imagine any other way to operate. Maybe I am missing something, but I don't think so. Convince me! I mean how do you fill in the forms? Yes calculation, but I am not convinced that is kosher. For instance you can find that there are big variances between R1/R2 + Ze calculation and Zs measured with an MFT.

I agree with you they is differences from calculations and actually measured results and I use to always do live tests at previous company
But I’m just following what this company requires us to do and that is calculations for zs results and not to do live testing apart from ze and rcd tests

 

[pc1966]

The place I work also tells us we are NOT to work live.
Dunno how the hell we're supposed to complete EICRs.

Odd. There is working live and working LIVE.

Originally I assumed that "working live" was the sort of high-risk activity such as making a change/repair to an energised system, you know the really squeaky-pants time and not something you would ever do unless there really was absolutely no alternative.

But of course any energised testing is also "working live" and then it gets more complicated as typically EICR and EIC both requier measurements such as Ze and Zs to be done, along with RCD trip-testing. Just how much exposure is too much to be safe?

• Do you base it on where you test (i.e. the CAT-II final point versus CAT-III DB location idea)?
• Do you base it on available arc-flash energy?
• Do you base it on whether it is done via probes or a 13A socket?
• If so do you leave light circuits untested, so the owner/occupier is the first one to encounter a problem?

 

[westward10]

Odd. There is working live and working LIVE.

Originally I assumed that "working live" was the sort of high-risk activity such as making a change/repair to an energised system, you know the really squeaky-pants time and not something you would ever do unless there really was absolutely no alternative.

But of course any energised testing is also "working live" and then it gets more complicated as typically EICR and EIC both requier measurements such as Ze and Zs to be done, along with RCD trip-testing. Just how much exposure is too much to be safe?

• Do you base it on where you test (i.e. the CAT-II final point versus CAT-III DB location idea)?
• Do you base it on available arc-flash energy?
• Do you base it on whether it is done via probes or a 13A socket?
• If so do you leave light circuits untested, so the owner/occupier is the first one to encounter a problem?

No someone has decided live not safe, simple as that.

 

[ipf]

No someone has decided live not safe, simple as that.

Because they reckon that, nowadays, the average spark can't handle it, must be the explanation, In other words, more dumbing down of the trade.

 

[Vortigern]

@Lt1990 is only carrying out works in the way as suggested by his company.

Obviously.
I wasn't castigating the OP more the company.
I think regulation 14 and a) b) c) have been interpreted extremely tightly. The observation was more that there is no real life measurement for compliance with ADS and I conclude the risk associated with that is higher (unreasonable) (even within reg 14) than the reasonable test. It may well be the insurers have said if anyone works live we will not cover you, end of. But as a tester you might also apply "reasonable" to your own tests. I am not working near a live conductor. Any such conductors are enclosed i.e. in a socket or ceiling rose if I use the lightmate (kewtech) Testing sockets with the plug adaptor if seen as a risk then puts the idea of plugging in any appliance could also be seen as a risk due to "working live" and as a BA1 person plugging in the hoover....

 

[cireland]

Worked for South Lanarkshire Council for a bit. They also had a blanket no live working policy.
They even gave me a set of aluminium steps and when I questioned it the response I got was
'you're not working live so what difference does it make'.

 

[timhoward]

The observation was more that there is no real life measurement for compliance with ADS and I conclude the risk associated with that is higher (unreasonable) (even within reg 14) than the reasonable test

It’s an interesting discussion.
I can think of countless times where live Zs has been lower than Ze+(R1+R2), some TT cases where parallel paths have even thrown it into TN level readings.
I’m trying to remember if I’ve ever had one read worse and I’m not quickly coming up with a scenario where that is in fact possible (resistances in parallel formula). Any ideas?

What I do like about the live Zs test is that it serves as a final check that everything I’ve disturbed for testing has been put back together adequately!

 

[brianmoooore]

Main conclusion I've drawn from this thread is that the world has truly gone mad.

 

[nicebutdim]

I work a lot under some of the most insanely rigid health & safety rules imaginable. Don't want to go into details, but you couldn't make some of it up. Of course they forget all about those rules, when processes trump safety, and have you working in live busbar chambers.

 

[timhoward]

Unlike me, here's a controversial thought....

As the company are apparently happy enough with pushing GS38 probes into a stationary main switch for a Ze, it would be interesting to know what they made of the Zs trick in the Kitcher book.
I've mentioned this more than once before, but it doesn't seem to be commonly known or used, so I'll bore people again:

Lock off circuit.
Prove dead at furthest point.
Add temporary link between R1 and R2 at furthest point.
Do 2-wire high current loop test between a live source (bus bar or top of main switch) and the top of the locked off and open breaker or RCBO.
Remove link (or take a jump backwards when breaker jumps straight back open having proved ADS works a 2nd way )

This is extending the CPC back from the end of the circuit to the CU using the live and allows a more accurate high current loop test.

Everything stays in terminals the board end.
Everything is dead at the point the difficult end is exposed and worked on.
It's only not-dead for the very short duration of the actual high current test.

If they allow Ze and RCD tests I can't see why they wouldn't allow this. You'd also have more accurate live Zs results than anyone else!

 

[ipf]

I work a lot under some of the most insanely rigid health & safety rules imaginable. Don't want to go into details, but you couldn't make some of it up. Of course they forget all about those rules, when processes trump safety, and have you working in live busbar chambers.

Just shows you what matters with a bit of financial pressure. Frightened $hitless when it comes to a loss of profit. Actually, that's one of the main reasons for H+S, to prevent pay outs, but when it comes to the crunch, they gamble.