Consumer Unit Change

[Pete999]

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

Just a point how many times have you measured r2 could be an iffy connection on your MFT's leads

 

[Nickj]

Hi Pete, thanks for the input.

I checked it at different points of the cable, used a wire brush to clear any surface tarnish. I couldn't believe the result, sadly it seems real.

 

[Pete999]

Hi Pete, thanks for the input.

I checked it at different points of the cable, used a wire brush to clear any surface tarnish. I couldn't believe the result, sadly it seems real.

Are the croc clips making contact properly?

 

[telectrix]

if the fault is between the last socket and the CU, as there are not many sockets on the circuit, you could diss. the faulty section (at CU and at socket) and convert to a radial on a 20A MCB. just a though to save cost.

 

[Midwest]

Good luck Nick with your assessment, and you've have been given some good advice by members, especially fault finding!

As regards the fixings for the CU, I take NDG's point, but I do not think that relates to the fixing of CU's more to that of cable supports in escape routes. reg 421.1.201 was all to do with (so I'm told), remove a source of fuel (plastic CU) from the source of a fire. So sealing holes (intumescent), fixings etc don't relate.

As regards using a plastic enclosure above a CU to extend cables, I was advised by Elecsa Tech support a while back (wrongly IMO) that such an enclosure would not comply with the reg, and could not be used in such circumstance. Now that we've had some time, to allow for the dust to settle as it were, I have asked Elecsa for some clarification on the subject. Thought you should perhaps know this before your assessment, just in case. Having said that, when I had my recent assessment, the Elecsa Inspector raised his eyebrows when I told him of the advise given.

Personally, I would use MF joint boxes, in ceiling void above CU, if the cables weren't long enough to terminate in new CU or Ideal in-line splice connectors inside the CU. I would only do that for one or two circuits. Anymore, and I would consider part rewire.

 

[tony mc]

I know faults can be a real pain to find especially when you have been looking for some time!
You say the fault is the last leg or first leg to a S/O from the CU and a CPC fault.
I would be inclined to join L/N at one end and take a reading just to see if the maths matches up with the distance to the CU just in case its a way out reading and the cables run goes elswhere.
Just my opinion as I have come across strange cables runs with no logic in the past!

Good luck with your assessment!

 

[westward10]

I love fault finding, it is the bit before I find the fault which is an ---.

 

[Nickj]

Ok so decided to lift floorboards to satisfy my curiosity. Cable went to an unused and totally forgotten about socket in a cupboard in the hall!

There was a loose connection in that. tightened up and I'm now getting 0.95- 1 ohm.

One would expect it to be 0.7 ohms or so.

My question is, would you continue fault finding to find where the last 0.3 ish ohms are coming from or would you (and my assesssor) agree that as it's close to expected value it's fine?

 

[Octopus]

I would remove the "last" socket and test the Zs on each leg of the ring to see what the readings are like - then consider the options......

 

[Midwest]

The purists will argue you should. But you will have to round to each connection, undo & re-terminate. Your first assessment, your choice. Of course you could argue what you have done thus far has improved the installation, and you determination to locate the fault, might impress your inspector. Perhaps try the former, but you will need to draw the line somewhere, think your Zs' was good?

 

[westward10]

Are they definitely 1.5 cpcs and not 1.0.

 

[Midwest]

Wonder if OP reconnected old socket (faulty leg). Perhaps temporarily remove socket and replace with strip connectors or similar. Good point re the cpc sizes Westward though.

 

[Midwest]

Could even be imperial sized cable, bit before my time, cough, so don't know how they compare L/N to cpc?

 

[westward10]

Could even be imperial sized cable, bit before my time, cough, so don't know how they compare L/N to cpc?

I think the cpc on imperial size cables weren't much different to the line size.

 

[Pete999]

Could even be imperial sized cable, bit before my time, cough, so don't know how they compare L/N to cpc?

7/029 Live =3/036 cpc I think will look for a comparison chart when the vino has worn off.

 

[tony mc]

He said the cables were solid as he was asking for extending advice and imperial are stranded and better cables IMO!
Could be older 2.5 T/E with 1mm CPC!

 

[sparksburnout]

7/029 Live =3/036 cpc I think will look for a comparison chart when the vino has worn off.

Pierre or you on the **ss every evening?

 

[Pete999]

Pierre or you on the **ss every evening?

Thursday off

 

[Pete999]

Pierre or you on the **ss every evening?

Not on the ----, just like the odd glass, nothing serious, it's just people's take on my posts, aint really been on the razz for many a year or two, had my fill of that during my world tour, red wine is my tipple, now I'm retired, but er in doors has got me on a shed building course for OAPs, of course I will be asking advice on how to run a supply to the sheds I build. LOL

 

[DPG]

Make sure you TT it. Wooden shed, so got to be a wooden earth spike. No, hold on a minute - that wooden work. OK, I'll get me coat. Daz