70s house, aluminium conductors

[Pete999]

Good idea, ferrules would give them a bit of back-bone wouldn't they.

Yes, I'm wondering if they ever complied. I have a copy of 14th ed amended to 1976, there's a table of copper clad aluminium down to 1.5mm² but for plain aluminium, minimum is 16mm². I suppose it could have been different in previous amendments though.

I seem to recall that there was a sort of rule of thumb in the days of Al cables that you went up a size from CU ie 2.5mm2 for lighting 4 mm2 for RFCs, certainly remember the complaining that went on w ith regards to using 2.5mm2 for lights, trouble connecting them, same with Sockets, all very well using Al but it took some time for manufacturers to realise that accessories needed to be redesigned to allow for the larger cables. Surface clipping was a pain as well.

 

[Lucien Nunes]

I agree with Davesparks that twin cable, and in some cases twin and earth, was in general use right from the beginning of sheathed wiring cables.

Obviously, with conduit installations, which were popular for domestic wiring in the 1930s, single-core VIR was universal and would loop in as appropriate, line at the switches and neutral at the lights. With sheathed cables, whether TRS or lead-sheathed, joint boxes were popular, with a twin run, twin switchdrop and twin to the rose, or alternatively a 3-plate rose.

With lead-sheathed, the earth goes everywhere a cable goes, provided the sheaths are interconnected at the fittings. This was done with (now confusingly named) bonding bars and bonding clamps, while junction boxes for lead-sheathed had these clamps built-in, designed for flat twin or flat triple cable. Even during the 1930s, some manufacturers were offering lead-sheathed cable with a tinned copper CPC, to reduce reliance on an effective connection to the lead (which was known to be troublesome) and to make it possible to terminate the CPC to a fitting e.g. a 3-pin socket without need for bonding clamps. With TRS, ordinary twin was the most common; when an earth was required it was sometimes run separately.

One odd single-core variation from the 20s / 30s where the line loop was always done at the switch, and the neutral not at all, was earthed-concentric wiring such as the Stannos system. This was true TNC with a combined neutral / earth throughout, via the metallic sheath. With earthed-concentric, the neutral goes everywhere a cable goes. At a switch you have three single-core cables - the feed, the loop and the switched feed to the light. At the light, just one single-core, with the neutral picked up from the sheath via the box or casing. Threaded sweating thimbles and threaded spouts were used to ensure a reliable CNE connection.

 

[davesparks]

The diameter measured is 1.1mm which calculates to 0.95mm2 - so it is 1mm2

Twin and twin and earth only came into use in the late 40's, prior to this, it was single cables (double cotton /rubber covered), the practice was the live would run to the switch, then on to the next switch, with only the switch wire going to the ceiling rose, the neutral would just go rose to rose.

Yes, I didnt think I'd drunk that much last night but apparently my ability to read a micrometer and do simple maths had vanished.

 

[ipf]

Copper plated aluminium and aluminium cables were all around the same, plated was ever so slightly lower, I think 1.5mm2 was 11A, and 2.5mm2 was 15A - clipped direct twin and T&E hence all the rings had to be in 4mm2 which was 19A

Only MK made fittings that were suitable - they clamped the cable and could take 2x4mm2, everything else was either too small or just used a screw - the aluminium flowed, oxidised and lost proper contact.

These were removed from the 14th in the 1976 ammendment, I think it was table 24M

But the smallest used was 1.5mm2 - I think the imperial 14th which was pre '70/72 may have had smaller cables!

As has been said, it needs a rewire, sounds like the cables have reached their end of life, once they start breaking, you will be forever repairing them!

You're not far off Julie. Table 24M was removed in the amendment. Below is table 26M.
Your current ratings are for 'bunched and enclosed' copperclad. As you can see (below), they're a bit higher for clipped direct.
Also, they're for 'coarse' excess current protection. Multiply by 1.33 for 'close'.

 

[Lucien Nunes]

Also, thanks for the offer of the redundant cable based on the planned rewire. I can see the time is fast approaching where we have to actually pick out some fittings and start building these demo boards. It's nice to show both cable samples sectioned and framed and also the same types of cable 'installed' in mock setups with some real working fittings (albeit at 12V) and some points opened up to reveal the wiring. Sounds fun to make but actually quite a bit of work, beginning with finding the right wallpaper for each era.

 

[Julie.]

You're not far off Julie. Table 24M was removed in the amendment. Below is table 26M.
Your current ratings are for 'bunched and enclosed' copperclad. As you can see (below), they're a bit higher for clipped direct.
Also, they're for 'coarse' excess current protection. Multiply by 1.33 for 'close'.

View attachment 54909

Yeah, I would have been thinking of column 11 - twin core in plaster etc. Rarely did we really use anything else in practice, as everything would eventually get to be run in plaster at some point.

Different now with wall voids and insulation.

Not that I ever installed aluminium, merely fixed/replaced/added to it.

And yes, that was for rewireable fuses (is there anything else???? )

Bit before my time, honest gov'

 

[Chris1234]

I’ve not read the whole thread, but from memory aluminium has around half the conductivity as copper, so best to check MCB ratings.
In a previous life I used to use titanium conductors (with Wago’s) with is around half the conductivity of aluminium!

 

[Pretty Mouth]

Also, thanks for the offer of the redundant cable based on the planned rewire. I can see the time is fast approaching where we have to actually pick out some fittings and start building these demo boards. It's nice to show both cable samples sectioned and framed and also the same types of cable 'installed' in mock setups with some real working fittings (albeit at 12V) and some points opened up to reveal the wiring. Sounds fun to make but actually quite a bit of work, beginning with finding the right wallpaper for each era.

I've got a few more bits n bobs that may be of interest, an old wooden fuse box and some old switches and sockets.You're welcome to them if they can be of use to you. I'll send details when I've got the cable ready to send you.

I sometimes come across old steel conduit that uses couplers to clamp together, and has what I believe to be rubber singles (red and blue IIRC?). Usually found in lofts, and would have been used for the lighting. Was actually still in use on a job I worked on recently, although in terrible condition at the accessories. Any idea what era this would have been installed? I'm guessing 1930s to 50s judging by the age of the properties I find it in.

 

[Marvo]

Thanks for the follow up info, it's a very interesting thread.

The photos you posted are textbook examples of how aluminium wire and terminations are problematic.

Wagos sound like a sensible solution, I'd clean the wire thoroughly first and maybe even some inhibitor paste depending on what the Wago maunfacturers instructions have to say.

 

[Lucien Nunes]

Yes it's interesting to hear of the specific problems that we attribute to aluminium, actually all happening in a real installation (although not so much fun for the owners of the property).

There's an interesting aspect to the use of the porcelain Scruit connectors. With copper cable, the conductors make electrical contact wherever they touch, while the porcelain body of the Scruit only serves to apply a clamping force (by the tapered screw action) and insulate the joint. When correctly fitted (many weren't) and not overcrowded, Scruits were actually quite reliable and effective on tinned copper. But with dry Al cable, contact is only made where the oxide is scraped off or bitten through, e.g. by the tip of a screw or the serrations of a cage clamp. The wire-to-wire contact in a Scruit doesn't get its oxide scraped off, so is only likely to be punctured in tiny spots as the copper cold-flows at the high spots.

Wire nuts in the USA have a steel spiral spring inside that forms the screw thread, which bites better into the conductors and holds them more securely than plastic or porcelain. In the case of Al cable, it's a mixed blessing. It will definitely scrape off the oxide and make a connection to itself, but if the oxide stops the conductors contacting each another directly, this diverts the entire current through the spring of the wirenut. Being steel and of typically higher resistance, it can work like a tiny heating element even while the circuit appears to work normally as there is no loose connection as such. There have have been documented examples of wirenuts overheating dangerously through this effect, whereas with an old British porcelain Scruit, the circuit would probably just go dead.