CU Change

[walec]

Hi Guys,
Just been to quote a job for a CU change, not a problem but I noticed some cable cores were silver (all red & black sleeve), the rest copper R&B sleeve. I assume this is aluminium but I have never seen this before, I know it could probably do with a rewire but if I change the CU only at this moment in time, does that conform as long as it tests OK?
Cheers

 

[Madjick]

hi

Alu conductors were about years ago, they became more popular because of copper shortages in the 70's. So you come accross them now and again.
They are much more brittle than copper and its really down to an assessment of their state, including insulation and subject to test.

I'd also check that they are of the correct size, you usually find that they are a size higher than copper, e.g 4.0mm used instead of 2.5mm for ring main. This is due to alu having a higher resisitivity than copper. So check they are suitable.

They should be ok but due to their age the insulation may have broken down a bit and also become dodgy, and if stranded cored the ends may become brittle so i'd avoid moving them about more than neccessary.

From a peridoc inspection point of view, you may wish to assess that under an observation and recommendation - depending on their state - that they may require improvement under a 2 classification.

 

[drywax]

Just changed a light fitting wired with that stuff and the insulation just crumbled in my hand so they've opted to get a rewire when I showed them the evidence

 

[steamboatwilly]

Walec.....Continuity and Insulation Resistance checks should give you the answer you need.

 

[electricAl]

Only you can know by looking, but entirely possible they`re actually tinned copper - in which case they`d still be candidates for rewiring but may still comply if testing proved sound. However, look carefully, as if they are tinned copper they may well be imperial sized which generally means a smaller CSA. Some circumspection called for then.

 

[mechelec]

Hi Guys,
Just been to quote a job for a CU change, not a problem but I noticed some cable cores were silver (all red & black sleeve), the rest copper R&B sleeve. I assume this is aluminium but I have never seen this before, I know it could probably do with a rewire but if I change the CU only at this moment in time, does that conform as long as it tests OK?
Cheers

Are you sure they are not stranded tinned copper as early twin and earth was. The larger sizes were due to them being imperial sizes

2.5mm was 7/0.029
1mm was 1/0.044

 

[walec]

Thanks for your replys guys.
Been back today and taken a closer look, they are stranded tin plated wires, did some testing and with the exception of low IR tests showing around 50Mohms all seems ok. Continuity and Zs was ok.