Does this need certifying and why?

[JohnW2]

On a ring circuit, the Zs value should be the same at every outlet.

That couldn't possibly be true.

It isn't, clearly a mistake. I was thinking of the other tests done on rings where the ends are linked together first.

Ah, right - yes, I see what you meant to say - I'm reassured to see that I'm not the only person who sometimes thinks one thing and writes something different

Kind Regards, John

 

[ericmark]

Your readings seem OK to me. No problem.

The Zs values increased the further I got from the consumer unit in quite a consistent fashion to give the maximum 0.62 Ohms at the furthest outlet.

On a ring circuit, the Zs value should be the same at every outlet.
Increasing as you get further away from the origin indicates it is a radial, or a ring which has been broken somewhere. If the protective device for the circuit was selected as if it would be a ring, it will now be the wrong one.

Although doing a loop test with no power the readings will be the same at every socket unless a spur. Zs refers to the total impedance socket to supply transformer and this will change socket to socket.

Using a earth loop impedance tester the pass value is 1.44 Ω where there is no RCD. With a RCD still need a reading of 1.44 Ω or less line - neutral but the line earth can be much higher.

Some meters and I stress only some auto change from measuring line - earth and line - neutral when switched from PSCC to loop impedance with a B32 MCB or RCBO the short circuit current should be over 160 amps. With C or D type it is much higher.

 

[JohnW2]

sounds like my Zs values were behaving as expected.....great

Indeed, certainly 'conceptually. If your figures are numerically correct (and if we're talking about 2.5mm² T+E), with a difference of 0.35Ω between the closest and furthest socket, that would imply that you have a somewhat longer ring length than the 40m I used for my graphical illustration (for which the difference was 0.23&#937. Is that credible (in terms of what you know about 'where the ring goes')?

Kind Regards, John

 

[JohnW2]

Although doing a loop test with no power the readings will be the same at every socket unless a spur.

Are you 'doing the same thing' as flameport, and talking about something other than a loop impedance test (e.g. a test in which you cross-connect conductors at the CU and measure L-N resistance at each socket?), since, as you go on to say...

Zs refers to the total impedance socket to supply transformer and this will change socket to socket.

Kind Regards, John

 

[samohtom]

I reckon the ring length is more like 30m or so kinda tricky to guesstimate...I'm assuming you're talking about the length of one set of conductors alone. If it makes any difference it is 2.5mm cable but only 1mm cpc not 1.5mm.

 

[EFLImpudence]

Yes the length of the cable.

Your figure of 0.34Ω for the end-to-end measurement relates to a length of 46m.

 

[JohnW2]

I reckon the ring length is more like 30m or so kinda tricky to guesstimate...I'm assuming you're talking about the length of one set of conductors alone.

Yep.

If it makes any difference it is 2.5mm cable but only 1mm cpc not 1.5mm.

Aha (it must be pretty old cable!) - that's probably just about right to make your Zs measurements more-or-less 'as expected'.

Kind Regards, John

 

[scousespark]

how many guys would just lend their kit to someone they only just met?

My guess would be zero. An electrician without test kit cannot do the job, so why would anybody hand theirs over to a diyer? Would anybody in here do that?

 

[EFLImpudence]

No. I wouldn't.

Apart from lending to someone, I wouldn't leave them in a workplace, even if I was the only one with access, because sod's law would mean I would need them and have to go and get them.

 

[samohtom]

I guess I am literally 5 minutes around the corner from him, he knows where I live and he tries not to work weekends...but still very generous. I stuck new batteries in his Megger as he refused to take any cash!

 

[scousespark]

He can't sign the job off because he didn't do the work.
The use of Wagos is irrelevant, apart from you stating that this electrician didn,t know they could be used and told you to twist conductors together.
AFAIA twisting conductors has never been allowed by BS7671.

He then said he couldn't test and gave you his Megger to do it yourself.
As EFLI said, we have no idea whether we will need our kit over a weekend. Even if we don't normally work weekends. There is also no way he could know your ability and therefore the risk of turning up on Monday to pick up a wrecked tester.

I know all my customer's address, but I wouldn't leave my tools with them.

 

[samohtom]

Erm, he did know they could be used and he didn't tell me to twist conductors together - I never said that...

Out of curiousity, what are you supposed to do if you don't twist them and don't use Wago's and have say 3 to go in somewhere? I know I'd rather have ones solidly twisted together than 3 bent over and screwed in with one screw, but maybe that's just me. Better be careful as this comment could start a whole new thread

I guess he's just a really nice guy!

 

[JohnW2]

Out of curiousity, what are you supposed to do if you don't twist them and don't use Wago's and have say 3 to go in somewhere? I know I'd rather have ones solidly twisted together than 3 bent over and screwed in with one screw, but maybe that's just me.

Intuitively, I can sympathise with your view, and it's not all that long ago that twisting multiple conductors which were going into the same terminal was pretty common/'standard'. However, the fact is that (particularly for solid, rather than stranded, conductors), twisting can damage/weaken/break the conductors, which is why the practice is now frowned upon - in favour of just 'screwing them all in with one screw'. Twisting is also a nightmare when one wants to remove conductors - e.g. for testing.

Kind Regards, John

 

[scousespark]

Erm, he did know they could be used and he didn't tell me to twist conductors together - I never said that...

Out of curiousity, what are you supposed to do if you don't twist them and don't use Wago's and have say 3 to go in somewhere? I know I'd rather have ones solidly twisted together than 3 bent over and screwed in with one screw, but maybe that's just me. Better be careful as this comment could start a whole new thread

I guess he's just a really nice guy!

I misread your post, but the number of connections has no bearing on whether he can certify the job. You posted that you were looking at putting a DSO into a ring with a spur to an FCU. Where are the wagos in this circuit? You did the work, so he can't certify it, you can.

 

[ban-all-sheds]

Well, no.

Looking at the questions he has asked, and the assumptions he has made, I honestly do not think that he does know enough about BS 7671, and testing, to be able to justifiably sign an EIC/MEIWC.