Browsing through some TGL documents I noticed, that the governmental construction in the German Democratic Republic used ring circuits in all apartments. 10A ring, wired with 2,5mm2 aluminum. Usually 2x2,5mm2, grounding achieved by installing a jumper wire between neutral and ground at every receptacle/light fixture.. After 1984 mandatory RCD protection for kitchens and bathrooms-> 3x2,5mm2 aluminum.
There was a brief spell in the late 1960s early 70s when the Rohdesian copper crisis was at its peak when a cable was introduced by BICC called copperclad it was a high-brid aluminium/copper mixture. Soft as sx@! loads of trouble with terminal screws cutting through soft cable cores. Big bulky conductors as well only remember it lasting about twelve months thank the lord!.
East of the iron curtain aluminum was big thing. My only question is. Where on earth does that get you? A British ring is ínstalled because you can fuse 2,5mm2 Cu at 32A. The GDR ring is wired with 2,5mm2 Al, could be fused 16A in case of a radial circuit and maybe 20 or 25A with a ring. But it was fused at 10Amps! And I can't imagine they ran any superfluous wires!
If you use the neutral for grounding, there is a risk of the neutral breaking somewhere and energizing whatever "grounded" equipment there is. By making a ring of it, you reduce this risk significantly, as both sides would have to break. If there is a 1% risk of a break in the neutral of the radial, the risk of failure on both sides of the ring only 1% * 1% = 0.01%
By using a small fuse, you limit the voltage drop. A 10A ring would have a very small voltage drop unless it is very long. That doesn't matter much if you have a separate grounding wire, but if you use the neutral for grounding it could: The ground at each outlet is at almost the same potential as the next one. If you plan how you put the outlets on the ring, I imagine you could minimize stray currents in the building. (Of course, that is a non-issue with an ordinary three wire installation)
[This message has been edited by C-H (edited 09-07-2004).]
Still, the main issue back then was to save as much metal as possible. Western Germany used the neutral of radial circuits as a ground without any scruples for decades, so I doubt the GDR would have acted any different. Guess I'll have to ask the guy I got the link from.
Indeed this is a TN-C system. According to today's regulations it's only allowed using wire sizes of 10mm2 and up, basically restricting it to feeders in a TN-C-S system, i.e. TN-C up to the splitting point, TN-S all the way to the sockets. In Western germany TN-C in residential wiring was prohibited in 1973, in the GDR in 1990. In both parts of germany many old systems remain in use. The use of an RCD is impossible with TN-C and if the PEN breaks grounded parts can be live at 230V. That's also the reason for the >10mm2 rule, they say such a big wire is far less likely to break than a 1.5mm2 wire. Fortunately we never had TN-C in Austria, it's a really ugly system.
which I copied over from here . Sinegoriye in the Russian Far East. The 'grounded' extension has been wired with two core cable. How they keep track of which is neutral when beneath the single grey insulation there are just two identical silver aluminium wires, I do not know!
[This message has been edited by Hutch (edited 09-30-2004).]