Useing and joining copper coated aluminium cables

Hi all,
We recently moved to a 70s house, where from the survey, and my inspection pre sale, the electrical installation was in pretty good nick, if somewhat limited in numbers of sockets.
Having now spent the last few months crawling around the innards of the house I now have a much more comprehensive understanding of the electrical installation, and one item that initially worried me was that the power cables, and some of the lighting cables, are in PVC insulated copper coated aluminium cable. However, despite the well documented problems in the US with plain aluminium cable, this Cu/Al cable seems OK. The PCV is flexible, showing no sign of cracking or leaching, and the copper wire surface is bright, and showing no sign of adhering to the PVC. I've now replaced about half of the rather tatty 13A sockets, and most of the light switches, and none of the connections were showing signs of creep, oxidation, heating, and other nasties, which accords with the comment in http://wiki.diyfaq.org.uk/index.php?title=Historic_Mains_Cables re this type of cable.
The ring cable has seven strands for phase and neutral, with an overall diameter of 2.3mm, and a single strand CPC of 1.3mm diameter, which in terms of its performance looks to me like a composite of imperial copper 7/029 equivalent for phase/neutral, and the equivalent of 1mm metric copper CPC. Lighting cable has three strands at 1.4mm overall, and a 1mm CPC. Given that the rings are on the RCD side of the CU, and are fed via 30A MCBs, it seems to me that the cable can continue in service where necessary (with appropriate testing.)
I can't find any information on the current capacity and performance of Cu/Al cables - does anyone have any thoughts or info here, as to whether my assumptions as to their continued use are correct? The cables are marked "Enfield-Standard Johnson and Phillips 600/1000V Copperclad" incidentally.
Which brings me on to my second query. I now need to join a number of cables, and to do it neatly in a comparatively small space. The obvious solution is to use crimps, and the seven stranded cables will just go neatly into blue crimps. I would, of course, use a decent ratchet crimp tool. Given all the above a properly made crimped joint looks as though it should be fine, but wondered if the team has any experience here?
One last comment - the wiki section on crimping http://wiki.diyfaq.org.uk/index.php?title ble_crimping all looks very sensible and well laid out. I have one query though - the photos show three blue crimps for 2.5mm T&E, which looks right for phase and neutral, but I would have thought a red crimp (despite the unfortunate colour) would be better for the CPC. I would assume that crimps work best if matched fairly well in size to the conductor concerned?
Thanks for your thoughts and comments,
Charles F
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I remember the copperclad conductors being introduced. The copper was electroplated onto the aluminium during manufacture and overcame the problem of oxidation within the joints. The rule of thumb was to use a size up on the copper equivalent to compensate for resistance variation. As long as the electrician kept in mid the relative softness of the underlying material and didn't screw down so hard that the cable wa fractured it worked fine and from your findings is still doing so. I would be a bit dubious about using crimp conectors on the smaller sizes due to the work hardening of the aluminium substrate. You could of course use screw terminals and solder these if not accessible after installation. The solder will bond well to the copper coating but use non corosive flux.
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Hi,
Agree with above, also see:
<http://en.wikipedia.org/wiki/Aluminium_wire>
cheers, Pete.
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CJF wrote:

Blue are certainly acceptable, and I expect that red are probably ok as well.
The crimps in question:
http://wiki.diyfaq.org.uk/index.php?title ble_crimping#Select_suitable_crimps
have acceptable cable CSAs of 0.25 to 1.65mm^2 on red, and 1.04 to 2.63mm^2 on blue. So the 1.5mm^2 CPC of a 2.5mm^2 T&E would be ok in either.
The continuous current rating of the red ones is less - at 19A, but I would anticipate* that their fault current withstand time ought to be adequate to clear any likely earth fault.
* but don't have figures to hand to confirm - hence why I did not use one in the photo.
--
Cheers,

John.

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three
I
fairly
http://wiki.diyfaq.org.uk/index.php?title ble_crimping#Select_suitable_cri mps
Good point - I hadn't taken into account that the max current on the blue crimps was higher, and since blue and red crimps cover both 1.5mm and (just) the older 1mm CPCs in 2.5mm T&E, the blue ones therefore seem a better bet.
Charles F
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CJF wrote:

You can tell from the earlier photo that has two blues and one red, that initially I was going to use a red on the earth, but then realised I did not know for sure that its current capacity would be adequate under fault conditions. ;-)
With older T&E that has 1.00mm CPC, then there would be no downside of using red, and they would probably offer a better mechanical fit.
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Cheers,

John.

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I'd consider using blue crimps and overlapping the two CPCs (instead of butting them up end to end) within the crimp to maximise the contact area of the two jointed wires.
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