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dingbat/Damocles: Thanks. But I 'm not limited to only RCBOs am I in this context (assuming my connection to Mother Earth is sound). Can I also use MCB (Damocles says MCB Type B) then with a suitable disconnection time? I am struggling with the generic names for these circuit breakers. I am...

dingbat: thanks for passing by. Damocles wrote: 'The question of what supply you have and how good an earth it provides applies here. If the earth is not good enough, then you have to use an RCD.' Where I asked about RCD (with Type B), I was meaning to say RCBO (though I am not confident...

Thanks indeed for your replies Damocles, ban-all-sheds, securespark. ban wrote: 'it's disconnection times that limit the length of the ring, hence the different limits according to the type of protective device and the value of Ze.' Is Ze the earth loop impedance? Can this only be...

Damocles: my gas and water supply pipes are both over 30ft away from the electric supply (one of the two earths might well be the same earth clamped next to the gas meter though - being routed across the ceiling void of three rooms) but both gas and water mains are plastics pipe before they...

plugwash: I reckon they are for high-tensile support in rough weather, besides why are they not separately coded? Don't they need single-core for digital type signals? Someone must know...(bugging?)

dingbat: interesting, I suppose it's the same with barbed-wire, or even denim jeans. Unavoidably adopted because they function but don't change. securespark: no nylon stripper in the black 7-core Telecom cable around here, just 3 extra red re-inforcing steel-stranded cores.

ban: assuming I have a serviceable TN-S supply, then in regard to a new CU can I avoid having 'cbType2' protective devices? The OSG, page 42, Table 7.1, relates these to 58 and 46metres of maximum cable length. And if these figures are based on disconnection times only, could they actually be...

ban: you say 'Looks like TN-S, Not TT anyway, which is the only supply type which affects the CU.' Which one of these two systems (TN-S or TT) does not affect the CU please? There are no other extraneous metal parts at all in the vicinity of the two earths clamped to the cable, which might...

securespark: if an appropriate authority provided a proper earth terminal could you say now with any certainty exactly what type of supply I would have then? (see previous link to diagram)

I love Stanley knives, they are so English. Particularly the classic model before they made them unnecessarily streamlined (I have collected four old ones). I have used one handle for forty years! Their great feature is that new blades are sharp. You can get new blades anywhere). It is always...

ban: you say, 'they are connected to the right place...' might this observation imply you think I have a TN-S system, as opposed to a TT or a TN supply system? (this is like trying to find who my father was... I want to identify my supply system as it is probably something I cannot change; and...

ryanj: yes, the two 10mm earth cables are only clamped to the outside of the lead-like sheathing. securespark: one of the earth tails is attached to a protruding tab on the night metering timer. The other 'might' be attached to the back of the meter, and/or if not then it could go to the CU...

I hope this sketch will suffice? (Click on the thumbnail to enlarge scale) http://uk.pg.photos.yahoo.com/ph/[email protected]/album?.dir=/92ee

In short, is my particular supply a TT system? There are two stranded-copper earth cables (no larger than 10mm sq cross-sectional area, sheathed in green/yellow) bonded together to one of the two lead-coated cables from the steel pipe.

Scenario: 1908 large three-storey Midlands town house, re-wired over twenty years ago. I could not know if the supply system would be generically classed as TN-S, TN-C-S, TT or other. There is a short length of approx 2 inch diam steel pipe from the original solid floor under the stairs...

ban; many thanks. Thanks, AdamW, securespark.

AdamW Thanks. If it is the case that there is not a 50/60metre length of cable limit in a ring circuit (but see the two links, above eg) then my first three questions are probably theoretical, yes. That is why I asked them all, as everything becomes more critical when restricted by this limit...

ban; this site gives the 50metres for MCB, and 60metres for cartridge http://www.diydoctor.org.uk/projects/ringmain.htm RSVP (please look at my other questions too) biblio

AdamW, ban-all-sheds; I have come across the 50metre maximum cable length in a few places, here is a site eg http://www.diydata.com/planning/ring_main/ring_main.htm Please bear with me all of you (don't leave me in the middle of the river) please please please look at my other three...

breezer, 50 metres maximum cable length for an MCB, was 60 metres for cartridge fuse protection. I know about the 100 metre square maximum floor area. Thanks.