Consumer Unit Change

[Nickj]

I have previously tested it and all appears fine ~(so hoping for a straight forward swap - fingers crossed!) no signs of overheating currently and they are grouped together. I have not inspected attic as its cram packed full of items and I've been asked to avoid going up there if possible.

I'm a little wary of doing the maths in case it doesn't comply, the likelihood of there being insulation in the attic is high and once that and grouping de-rating are taken into consideration one may find it doesn't comply...what would you guys do then?

I'll tuck the wagos behind the breakers and make it as tidy as possible.

thanks to all so far, It's greatto be able to bounce ideas around, you're saving me from going crazy

 

[Pat H]

They won't inspect the attic. Say you checked what you could access and cables are clipped to joists so you are ok.
They probably are anyway.

 

[Nickj]

To pick up on what wilko was saying earlier regarding tails in a gland and internal clamp (if provided). Its fine if they are coming in with rest of cables to not use a gland? I'll secure cables with a clamp if it's provided (yet to pick it up so not sure whats in the box)

 

[westward10]

Don't worry about grouping or clamping, it is all rear entry. Undertake a neat job and you are halfway there. They will not ask you difficult questions as I said before they are not going there to catch you out.

 

[Nickj]

thank you very much! I'm generally neat and tidy with the installs and the testing should be spot on, hopefully i'll get through it

 

[HandySparks]

To pick up on what wilko was saying earlier regarding tails in a gland and internal clamp (if provided). Its fine if they are coming in with rest of cables to not use a gland? I'll secure cables with a clamp if it's provided (yet to pick it up so not sure whats in the box)

The question is: are the cables, and therefore the terminations liable to be disturbed? If not, no need for clamping.

 

[NDG Elecs]

Plastic wall plugs into believe are fine as the brickwork will act as a heatsink, well that is what I heard.

The link below makes interesting reading (if you have a spare 10 mins). There is a download at the bottom of the link.

Fire performance of cable supports - IET Electrical - http://electrical.----------/wiring-matters/58/bre-report/index.cfm

 

[westward10]

thank you very much! I'm generally neat and tidy with the installs and the testing should be spot on, hopefully i'll get through it

Well good luck keep us posted.

 

[westward10]

The link below makes interesting reading (if you have a spare 10 mins). There is a download at the bottom of the link.

Fire performance of cable supports - IET Electrical - http://electrical.----------/wiring-matters/58/bre-report/index.cfm

Interesting.

 

[Wilko]

The link below makes interesting reading (if you have a spare 10 mins). There is a download at the bottom of the link.

Fire performance of cable supports - IET Electrical - http://electrical.----------/wiring-matters/58/bre-report/index.cfm

Thanks for this ref, and thanks also @Nickj - Wall-dogs it is !

 

[Nickj]

Went to look at the board change again today and redid all the tests before commencing with the change.

All tests ok except ring final circuit is quirky.

Continuity of ring final:
R1 0.4 ohms
Rn 0.4 ohms
R2 29.8 ohms !!!!

High resistance joint somewhere, taken all the sockets off and checked, couldn't find anything. no spurs in house and only 5 sockets down stairs and 3 sockets upstairs (small house).

Surely there isn't a junction box for such a small house????

I forgot to note the Zs but it was an acceptable value.

Should I go searching for the high resistance joint (lifting boards etc - the fun) or as it has an acceptable Zs is it ok to leave it? (assessor questions)

Thanks all

 

[NDG Elecs]

Could easily have a JB anywhere in any house unfortunately! I would not be too happy with R2 of that value. I would suspect it's a discontinuous CPC and the 30 ohm value was through parallel paths of boiler/gas hob and such like. I would split the RFC in half/quarter/etc and retest both legs until you have a rough area where the issue is. Maybe disconnect the CPCs from the boiler etc to see if parallel paths are the reason for the high reading.

Did you do a Zs at every socket/FCU/etc? Not sure what the assessor would say, but my view is that it should be sorted.

 

[westward10]

Agreed you cannot leave it.

 

[Briggs69]

Hopefully, you will have slack to re term, if not as westie said, extend in CU.

Agreed extend in cu with wagos

 

[Octopus]

They won't inspect the attic.

ha ha.

Not come across an "inspector" yet who wants to get messy.... I did suggest an inspection to an Elecsa chap once which would have meant a trip into a "nasty" loft - he was not interested! He looked at the CU instead!

 

[1Justin]

You can't leave 30 Ohms r2. But you really don't need to start splitting the ring to begin to locate the fault. Several ways to do similar, but why not connect L-CPC at CU on just one cable of the pair. Nip round the sockets with your MFT measuring L-CPC and find the one where the reading jumps up. Bingo (or at least nearly so - because it could be at a hidden joint before that point). Reversing it can help you home in on it from both sides if that helps.

 

[Nickj]

I stayed late to find the fault. it's the return leg to the consumer unit that tests 30 ohms. Rest of ring tests 0.76 which is pretty much bang on what you'd expect.

The return leg is a very short run to the consumer unit and can't think what could be causing it.

My plan is to run a new return leg in conduit tomorrow when it's light.

That should then make all circuits good to go for the board change which I'll also do tomorrow.

Hate using conduit but at same time don't want to be chasing out and lifting floorboards (mammoth task as house is pretty full with furniture).

 

[NDG Elecs]

You say it's a fairly short run with the fault on it. I know what you are saying re lifting board etc, but if the floor was carpeted and boards accessible, I would be tempted to have a quick look to see if there are any small cut boards that are obvious access points to underneath. There may well be a JB there and it could be a quicker fix than running a new section in trunking. If there is a great big wardrobe in the way then maybe not though! Sounds like you found it pretty quickly at least mate.
Out of curiosity are there any sockets etc on the faulty leg? Are the IR tests all clear? Is it downstairs? Just thinking of possible moisture causing an issue with the last question.

Good call by 1Justin.

 

[Nickj]

No sockets on the leg, the faulty leg has an ir of >2000MOhm l-n, a little less l-e ~ 1800MOhm.

The resistance on the faulty leg:
L-l <1 ohm (forget the result)
n-n <1 ohm
E-e ~30 ohm.

I'm thinking it must be a junction box somewhere although why anyone would use one for such a short leg is beyond me!

Won't take long to put trunking up for a new leg, there is a lot of furniture there and using a tape measure to estimate where I'd need to look there is a wardrobe right where I'd need to lift

Must say, I can't wait to finish this job! Hopefully to a standard the assessor will be pleased with

 

[stitch]

Let us know how you get on.