70s house, aluminium conductors

[Pretty Mouth]

I visited a client about a week ago, an elderly couple complaining that their lounge, hall and landing lights were all flickering simultaneously with a noticeable buzzing noise. When I arrived the lights appeared to be working ok (I asked them to switch them off until I could attend), so an intermittent fault. Opening up accessories revealed the likely culprit - aluminium conductors, the first time I have come across these.

Some observations:
House built 1973
1mm² (or so I believe, next time I'll measure w/ micrometer) single solid strands
Dull silver appearance, brighter when cut.
Not copper clad aluminium, not tinned copper.
Very soft and supple compared to copper.
Higher resistance values vs copper
Prone to breaking off where screwed at the terminations.
It was hard to get a clean reading by testing continuity with the probe placed directly on the bare conductors (CPCs were unsheathed), the reading would jump around constantly in the range of a couple of ohms. I presume this is due to the insulating oxide layer aluminium is said to form. Clipping a jump lead to the conductor and testing to that gave a steady reading, as did testing to the brass terminal where soundly terminated.
Other circuits in the house are, at a glance, aluminium also.

I did what I could in the time I had available - I went through the circuit (downstairs lights) checking and tightening everything, found several conductors broken or very nearly broken at the screws so reterminated those, and ended up with satisfactory R1+R2 vs RN+R2 results. Borrowed neutral on landing light as you would expect for a property of that age.

Anyway, received another call from them on Christmas eve, they had noticed a small flash and pop! from one of the bedroom wall lights when switched on. Also switching on say the main bedroom light would cause a momentary flicker on the landing lights. He also told me they had an intermittent problem in the past with the bathroom light flickering, and certain sockets sparking when switched on. Advised not to use dodgy lights and sockets until I can get to them in a day or 2.

The place is obviously due a rewire, and that's what I will recommend. In the meantime, I'll need to make good any problems. I understand standard accessories are not to be used with aluminium conductors. Apparently some Wagos can be used on aluminium conductors when used in conjunction with the Alu-plus paste:

Syringe (249-130) | WAGO GB

Syringe; Contents: 20 ml Alu-Plus contact paste (4017332133890) Online at WAGO GB!

www.wago.com

I was thinking of using this to connect a length of copper conductor to the ends of the aluminium conductors, then terminating the copper in the accessories. I have reservations though, I suspect the 1mm² aluminium will be too soft and bendy to force into a wago 773.

What have other members of the forum done in these circumstances and what would you recommend? As always, all information gratefully received

 

[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.