70s house, aluminium conductors

[Robson689]

I agree that a rewire would be for the best, hopefully they can afford it. As it stands I cannot say for certain that it has ever complied with the regulations, and I can find no data for current carrying capacity. Does anyone know if aluminium conductors would have the same CCC as copper clad aluminium conductors?

I'd imagine they have a lower capacity as aluminium has a higher resistance than copper

 

[Marvo]

Rewire the house.

Old solid aluminium conductors in domestic final circuit sizes will be a compliance nightmare with many, if not all terminations in modern electrical accessories not being suitable.

Old aluminium wiring is also a much higher fire risk in general.

If you really have to do repairs then maybe look on the USA version of ebay for bi-metallic ferrules and oxide inhibitor paste because solid aluminium house wiring was used more in the US than in the UK. If you're putting aluminium solid wire into a screw or cage termination then be aware it's as likely to fail because of overtightning as it is with undertightning.

 

[Julie.]

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!

 

[Lucien Nunes]

Agree - lighting circuits usually 1.5mm², nearest equivalent to 1.0mm² copper.
Rings 4.0mm², ditto 2.5mm² copper.

You can spot the MK fittings that were designed for aluminium because they have rising clamp terminals like DIN rail terminals or MCBs. I have some in use at home although not on Al cables; they are good terminals for any cable.

I was thinking of using this to connect a length of copper conductor to the ends of the aluminium conductors

a.k.a. 'Pigtailing' in the USA, where Al cables are much more common and this task arises more often.

Let me know if you get the rewire job. I am eager to get some good lengths of Al cable for the displays and demonstrations. I can convert it into your choice of beverage...

 

[lozarus]

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.
!

I have an MEM type socket in use here with clamp terminals, and also have a Britmac brand single which uses the same clamp mechanism. So I suspect there were some. Competitors!

 

[Pretty Mouth]

Evening all. First, a big thank you to you all for your comments and advice, it has all been really helpful.

I went to visit the job this afternoon. When I arrived, some of the lights (downstairs circuit) weren't working at all. Tried a few switches, then some lights started flickering, then came on full. Opened up accessories and a number of conductors had broken at their terminals, several being ones I had terminated myself last visit. @Marvo , you were spot on, the aluminium conductors do not tolerate being over tightened at all.

As a temporary fix I have used Wago 773s to join the ally conductors together and 'pigtail' a length of copper to terminate in the screw terminals of the accessories. The ally wires went into the wagos easier than I expected, and continuity was apparently sound after the fix. I imagine if the Alu-plus paste was used, this could be a good fix if anyone else comes across this problem.

Before I left I quickly tested the other aluminium circuits. The cooker circuit (10mm ally) tested fine, but the ring final (4mm) had problems end-to-end; 1400ish ohms on neutral and OC on earth. I assume this has been a long term fault as the breaker has been down rated to 20A by the previous spark. I'll have to take a look it it next week.

Anyway, the good news is they want to go ahead with a rewire in February, so there will be plenty of salvaged cable for you @Lucien Nunes .
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I measured the lighting conductor with a micrometer, it was indeed 1mm². A few photos:

 

[ipf]

Evening all. First, a big thank you to you all for your comments and advice, it has all been really helpful.

I went to visit the job this afternoon. When I arrived, some of the lights (downstairs circuit) weren't working at all. Tried a few switches, then some lights started flickering, then came on full. Opened up accessories and a number of conductors had broken at their terminals, several being ones I had terminated myself last visit. @Marvo , you were spot on, the aluminium conductors do not tolerate being over tightened at all.

As a temporary fix I have used Wago 773s to join the ally conductors together and 'pigtail' a length of copper to terminate in the screw terminals of the accessories. The ally wires went into the wagos easier than I expected, and continuity was apparently sound after the fix. I imagine if the Alu-plus paste was used, this could be a good fix if anyone else comes across this problem.

Before I left I quickly tested the other aluminium circuits. The cooker circuit (10mm ally) tested fine, but the ring final (4mm) had problems end-to-end; 1400ish ohms on neutral and OC on earth. I assume this has been a long term fault as the breaker has been down rated to 20A by the previous spark. I'll have to take a look it it next week.

Anyway, the good news is they want to go ahead with a rewire in February, so there will be plenty of salvaged cable for you @Lucien Nunes .
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I measured the lighting conductor with a micrometer, it was indeed 1mm². A few photos:View attachment 54897View attachment 54898View attachment 54899View attachment 54900View attachment 54901View attachment 54902View attachment 54903View attachment 54904

Are you measuring the csa….or the diameter?

 

[Pretty Mouth]

Are you measuring the csa….or the diameter?

Diameter then pi X r²

 

[freddo]

Good work! Must have been quite a fragile cable to pull in, even when new. Thank goodness aluminium cable is rare in domestic installations.

 

[lozarus]

Interesting I note that the metal back boxes have plastic threads on both sides?

 

[Pretty Mouth]

Interesting I note that the metal back boxes have plastic threads on both sides?

Yes, all of the lighting back boxes I opened had them. Have see them a couple of times before, similar aged properties

 

[freddo]

Very common for installations with wiring or switch drops with no CPC. Insulates the plate screws from the back box.

 

[lozarus]

Very common for installations with wiring or switch drops with no CPC. Insulates the plate screws from the back box.

Yes i figured as much. In this example it could make for a nasty swap if someone were to fit a class 1 switch and not link the CPC currently terminated in the back box to new metal fitting. Interesting stuff

 

[Julie.]

Very common for installations with wiring or switch drops with no CPC. Insulates the plate screws from the back box.

Yeah, that installation looks very odd, 1mm2 was not normal, nor would be the use of twin & earth on lighting circuits in that period, also running the neutral to the switch was old-style - a sign of the use of singles just prior to using twin cable.

I would guess that it was an old electrician following the 'old' ways with the new cable of the time!

Btw, since there is a new consumer unit (mcbs or cartridge fuses) then you can up the cable rating by 133% as it's no longer course protection, but I guess you would know that

 

[Pete999]

The conductors should probably be coated with an anti-oxidant paste designed for aluminium electrical terminations. I use Ideal Noalox, though it's usually on much larger conductors.

View attachment 54887rank Mate it's not help

The conductors should probably be coated with an anti-oxidant paste designed for aluminium electrical terminations. I use Ideal Noalox, though it's usually on much larger conductors.

View attachment 54888

Are you measuring the csa….or the diameter?

Diameter I should imagine, with a micrometre as the test instrument

 

[freddo]

Your links don't work!

 

[davesparks]

Yeah, that installation looks very odd, 1mm2 was not normal, nor would be the use of twin & earth on lighting circuits in that period, also running the neutral to the switch was old-style - a sign of the use of singles just prior to using twin cable.

I would guess that it was an old electrician following the 'old' ways with the new cable of the time!

Btw, since there is a new consumer unit (mcbs or cartridge fuses) then you can up the cable rating by 133% as it's no longer course protection, but I guess you would know that

Twin cable was in use for many years before PVC insulated cable came along, TRS or lead twin was widely used much earlier than that aluminium cable was installed.

In all the old books I have read or collected on electrical installation I think I've only seen neutrals at the switches as a relatively recent method.
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Are you measuring the csa….or the diameter?

Diameter I should imagine, with a micrometre as the test instrument

The diameter is being measured and the CSA calculated from that.

The diameter appears to be 0.210mm on the micrometer (if I'm reading it right) which gives a CSA of 1.03mmsq which is within a sensible tolerance of a 1.0mmsq nominal size.

 

[Julie.]

Double post for some reason - don't know how that happened
[automerge]1577491080[/automerge]

Twin cable was in use for many years before PVC insulated cable came along, TRS or lead twin was widely used much earlier than that aluminium cable was installed.

In all the old books I have read or collected on electrical installation I think I've only seen neutrals at the switches as a relatively recent method.
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[automerge]1577482107[/automerge]



The diameter is being measured and the CSA calculated from that.

The diameter appears to be 0.210mm on the micrometer (if I'm reading it right) which gives a CSA of 1.03mmsq which is within a sensible tolerance of a 1.0mmsq nominal size.

Ok I will try again, I appeared to have double posted, then when I removed one, both disappeared???!!!

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.

I think it was an old spark, continuing this idea, but with t&e ; and not someone trained with t&e, because almost straight away the three plate style of wiring came along with the new wire (rubber, and rubber/lead)

It was well before my time, but we ended up fixing/fault finding and replacing the old type wiring which was commonplace.

I think an old spark in the early 70's rewired the house following his old practices, but with the newest cable of that time - without following the associated wiring practice - He should of used twin - not twin and earth, with standard (of recent years) drop/3-plate method in 1.5mm2 (or 3/029 if really early 70's)

 

[Pretty Mouth]

Just to complicate matters, the hall and landing lights are 3 plate/ loop in at the rose (with obligatory borrowed neutral), and the bathroom is loop in at a junction box.

@Julie. , you also have a copy of the 14th ed of the regs, am.1976? I'd not heard of rewireables as being referred to as course protection before, until I saw it mentioned in the tables in it a couple of days ago. Also highly frustrating that table 24M is missing from it.

 

[Julie.]

Just to complicate matters, the hall and landing lights are 3 plate/ loop in at the rose (with obligatory borrowed neutral), and the bathroom is loop in at a junction box.

@Julie. , you also have a copy of the 14th ed of the regs, am.1976? I'd not heard of rewireables as being referred to as course protection before, until I saw it mentioned in the tables in it a couple of days ago. Also highly frustrating that table 24M is missing from it.

Yes, I have my old copy of the 14th, it is the one I started with!

Most of the guys at the time had older versions - although very few actually had the regs themselves, most had guide books - similar to the on-site guide, essentially a simpler version.

To be fair, things didn’t seam to change as much as today.

Came across loads of different ways of doing things, at college it was "this exact way or nothing" but every site we visited, you could see the evolution and mixture of practices over time