Inspection and testing turns into fault finding

[happysteve]

Eh up

So, I'm taking my 2394/5 exams at the start of December, and I'm coincidentally covering inspection and testing in my 2365. Thought I'd get some more practice in, having been appraised in (by my tutor) and confident with safe isolation procedure.

I've got a 16th edition Wylex board:

RCD-protected side:
2: Spare (32A)
3: sockets (kitchen+consevatory), 32A type B 60898 RFC 2.5+1.5 T&E
4: sockets (except kitchen + conservatory), 32A type B 60898 RFC 2.5+1.5 T&E
5: Shower (disconnected at isolator, replaced with boiler-fed shower), 40A

Non-RCD-protected side:
1: lights down+doorbell+porch light (spur at board), 6A type B 60898 RFC 1.5+1.0 T&E
2: lights up, 6A type B 60898 RFC 1.5+1.0 T&E
3: Water heater (disconnected), 16A

Ze = 0.10, Ipf 2.3kA, TN-C-S

I did some non-trip Zs measurements on the two RFCs. Circuit 4 looked fine and dandy: consistent readings through the house, between about 0.42 ohms and 0.50 ohms, except a couple that look like they might be spurs where it creeps up to 0.63/0.64 ohms - funnily enough, both of these are surface-mounted boxed, as opposed to recessed into the plaster. Then on dead tests, r1, rn and r2 all about right: 0.59, 0.60 and 0.97 respectively. R1+R2 followed nicely, between 0.31 and 0.42. All good

Circuit 3, however, is broken. Literally, as in, it's not a ring. Measured Zs reflected this: starts low at the end of the kitchen closest to the DB, (0.35 ohms), one of the kitchen sockets reads 1.35 ohms which is an anomaly, and Zs creeps up in the conservatory through 0.54 to 0.69.

r1, rn and r2 all show no continuity.

So I got my long lead out. Interestingly, one socket in the kitchen (on the wall closest to the DB) is on leg "A", whilst all the other stuff is on leg "B".

Will it surprise anyone that we had our kitchen done recently? I have left a message on the answerphone of the company that did the electrical work, I will give them the opportunity to put it right.

As a temporary measure, I have also swapped the 32A MCB for the 16A one that used to supply the water heater. Guess I'll have to avoid boiling the kettle when the oven's on.

That was as much time as I had before I had to pack up in preparation for picking up my son.

Some pictures:


Not the neatest installation, is it? A busbar cover would make me more comfortable, too.


Back together, the split ring now on a 16A MCB.

 

[Richard Burns]

Good one.
Isn't it interesting to find out how safe you thought you were!
It also highlights the reasons for dead testing first on new installations, since the dead tests would show that the circuit was non complaint and so should never have been energised....Oh dear!!
If you have just had your kitchen done then I am sure a detailed perusal of the supplied test certificates will show that the installer did everything correctly:whatchutalkingabout:aureola:
Fiction festival this way→→→

 

[happysteve]

Work of fiction: entirely! Either the R1+R2 value on the MEIWC is made up, leaving a potentially dangerous installation (which I would give a C2 on an EICR - would that be right?), or, he was the bugger who twisted the RFC CPCs together in the MET. Not sure which is the greater crime...

We're going to have words...

 

[Richard Burns]

Remember he could claim that the Zs value is OK because it is 30mA RCD protected so Zs only needs to be less than 1667Ω. But this is not really acceptable as you can easily have the circuit compliant.

However the potential overload of the cable on the long length of the leg, especially in a kitchen, would be more difficult to prevent attracting a C2.

You could almost bet that the circuit was tested at a single point for Zs and R1+R2 back calculated from Zs at the board, though you do not have to have R1+R2 on the MEIWC (Only Zs).

 

[happysteve]

However the potential overload of the cable on the long length of the leg, especially in a kitchen, would be more difficult to prevent attracting a C2.

You could almost bet that the circuit was tested at a single point for Zs and R1+R2 back calculated from Zs at the board, though you do not have to have R1+R2 on the MEIWC (Only Zs).

Agreed. And on the standard IET MEIWC you're right, this NICEIC Domestic Installer used a different form, though. I have cropped it to remove my and the installer's personal info.



Edit (extra stuff): As for Zs - I think this is satisfactory anyway for the MCB (regardless of presence of RCD), despite being on two radials (I have a low Ze, it was apparently 0.07 ohms in August, I measured it at 0.10 ohms on Tuesday). No, what was bothering me is the overload situation, especially since I (potentially) have a double oven, a kettle and a microwave all on the same leg - I say potentially as I didn't take the cover off the oven switch to determine what leg it was on.

 

[Richard Burns]

The 1.35 would not make it on the anomalous socket as that would then be a calculated Zs of 1.42Ω at 20°C with a limit of 1.16Ω.
interesting that you have a BSEN61009 RCD since RCDs are BSEN61008.
Type B RCDs are also rare especially since yours is a type AC.
However I am just being picky.

The results do look similar to your results but obviously did not include an end to end test.
I do not know an oven on the ring, tut tut:smile5:

On a practical basis there is small cause for concern but from a compliance basis this is terrible, if you did not have additional sockets added then it is likely that there is a missing cable connection at one socket (or that they damaged the cable between two sockets and so left it out!)

 

[happysteve]

The 1.35 would not make it on the anomalous socket as that would then be a calculated Zs of 1.42Ω at 20°C with a limit of 1.16Ω.
interesting that you have a BSEN61009 RCD since RCDs are BSEN61008.
Type B RCDs are also rare especially since yours is a type AC.
However I am just being picky.

The results do look similar to your results but obviously did not include an end to end test.
I do not know an oven on the ring, tut tut:smile5:

On a practical basis there is small cause for concern but from a compliance basis this is terrible, if you did not have additional sockets added then it is likely that there is a missing cable connection at one socket (or that they damaged the cable between two sockets and so left it out!)

Ha! This is rapidly turning into a "how not to do it" example!

When I said that I thought Zs was satisfactory, I was thinking more in terms of what was quoted on the (badly-filled out) form, rather than at the anomolous socket (which of course doesn't meet the required values of Zs).

Regarding oven on a ring - yep, to be fair to the electrician, he did mention that, but seemed reluctant to run an extra circuit at the time. He gave me a quote to run a separate circuit at a later date. Don't think I'll be taking him up on it, somehow!

Thanks for taking an interest in this, Richard, and thanks for your thoughts. I was initially kinda pleased that there was something interesting for me to fault find. Now I'm just peed off that it's a shonky (potentially) unsafe job!

 

[Richard Burns]

Stick with the being pleased to find and identify a fault, it is not worth getting angry about unsafe work otherwise you will be permanently angry in the domestic world!
Overall this is poor work but it is not going to be immediately dangerous and likely not to be a problem unless you are unlucky.
However this is not to say that it should ever be installed like that, and it is a basic error for the installer to have made and does need rectification.
This is the problem with bad installs that they can cause no discernible problem for a long time but if the chance occurs it could be deadly.
We are there to ensure such installs do not occur.

I have gone to a house with a disconnected neutral on a ring and searched about and found that about 15 years ago someone had split the ring to extend both legs out to more sockets!
On another house they had paid a fortune to have the electrics 'renovated' and the ring had been put on 2 x16A radials with the faulty cable left live in the back box of a socket, it had been there without problem for a couple of years.

 

[SirKit Breaker]

Steve,

How did you find the exams last week?

 

[telectrix]

by looking in the right place. he probably found them on the desk, where they were put ready for him. :smilielol5::smilielol5::smilielol5:

 

[happysteve]

by looking in the right place. he probably found them on the desk, where they were put ready for him. :smilielol5::smilielol5::smilielol5:

Why isn't there a tumbleweed smiley when you need one?

I found the exams alright, cheers Howard. I had a bit of a brain f@rt in the 2395, which I found a bit harder than the 2394. I got the distinct impression that the two exams weren't coordinated in any way. After the first exam I thought I had an inkling what would come up in the second... but instead they chose to ask (some of the) same questions again. That threw me a bit! I would put money on passing the 2394; if I don't pass the 2395 I will be surprised and disappointed, but you never know. Just another 6 or 7 weeks to wait... and the small matter of the practical tomorrow.

 

[happysteve]

Update: ^^^^ Passed (94 and 95) Also 2382 (meh). Got a final assignment on my 2365-03 to do, then, if it looks like I can get regular and varied work in, I'll sign up for the 2357 bridging module + NVQ and AM2.

Happy days

Thanks everyone who's helped on the journey so far...

 

[Plonker 3]

Nice one Steve.

 

[happysteve]

Nice one Steve.

Thanks Dylan.

Just having a peek at the examiners' report. 41% pass rate on the 2394. 52% pass rate on the 2395. I found the latter tougher. Need more experience, I guess.

 

[Plonker 3]

It will come, nobody knows everything. The main thing is you passed 2 exams that really do get you thinking.