Regulars will already be familiar with the diagrams of U.K. systems posted in the Technical Reference Area. I asked Nick (who converted my original rough sketches into the CAD line drawings you see) to add the TN-S, TN-C-S, and TT designations that those of you in Europe will be familiar with.
Thanks to Nick and to Scott35 for re-posting these diagrams. You can see them here .
All three of the systems are still in common use in the U.K., TN-S in older urban areas, TT mostly in rural areas, and TN-C-S (PME) almost everywhere now (originally only in certain rural areas).
Paul, Just a small question. Why are steel-wire armoured cables used in the UK?,when a neutral-screened cable could do the same duty?. Is it required by the Regulations for Mechanical Protection?. Are SWA cables still being used in U/Ground applications?.
Neutral screened: Do you mean just a concentric copper neutral? These have become the norm for new installations here now, whether overhead or underground, although for the latter they're enclosed within rigid PVC conduit for protection.
The old underground service cables that can still be found in many towns had a a solid lead armor.
SWA is still very common for underground feeders on the consumer's side of the meter, e.g. for a feed to a detached garage or workshop.
Paul, With respect to a Ring Circuit in a 2-storey house,would there be a ring circuit for each floor?. Also, with a Spur running off of it, what is the max. loading allowed on a such spur?, assuming that the spur wire is run in the same size wire as the Ring?, is it legal to use a smaller size cable, provided that is fused at a lower current rating, at the tap-off point?.
Re: U.K. Residential systems#134367 11/17/0205:10 AM11/17/0205:10 AM
Yes, a ring per floor is a very common arrangement, although I'd prefer to see the upper and lower floors each served by both rings as it will give a better load distribution.
The actual area served by each circuit is another aspect of the way rings are implemented here that I don't like.
Many references these days make mention of the heavier kitchen loads than in times past, but then suggest that a separate ring be installed to feed the kitchen. It still results in one ring carrying the bulk of the heavy loads while the others carry minimal loads.
Unfused spurs can be wired in the same size cable as the ring itself, i.e. usually 2.5 sq. mm. Such a spur is allowed to feed only one socket outlet or one fixed appliance. (A twin, or duplex, socket counts as one for this purpose). The original ring specifications allowed two sockets to be fed on a spur.
A fused spur can be wired in smaller cable. The ring spur units take the BS1362 fuse, the same type as used in 13A plugs.
Such fused spur lines are sometimes used where a ring is the most convenient circuit to tap, e.g. adding a wall light where it would be hard to run cables back to a lighting circuit. You could tap the ring with a fused spur, fit a 3 or 5A and fuse and run the light spur with 1 sq. mm cable.
[This message has been edited by pauluk (edited 11-17-2002).]
Re: U.K. Residential systems#134368 11/18/0201:08 AM11/18/0201:08 AM
Paul, Are you telling me that all of the equipment in the Kitchen are on the same Ring circuit?,I thought that they had a dedicated feed for things like Cookers and other heavy current users.:eek Like yourself, mate I don't agree with the Ring circuit,we are still finding the odd one over here, the differences being they never had fused plugs on them and sometimes you might be really lucky and find one that is fed by two fuses, not the two wires going into one fuse, a real Electrician Killer.
Yes, the range/cooker has its own dedicated circuit, but it's not at all unusual to find one ring feeding all of the remaining sockets in the kitchen, not only countertop receptacles for toasters, kettles, etc., but also those for a washing machine, dishwasher, and dryer.
Sometimes it's a result of the latter being added in recent years, but I've also seen new kitchens wired with a single ring to include all three.
The IEE rule regarding a maximum floor area of 100 sq. meters per ring is observed, but to my mind designs frequently ignore the requirement that this should also be subject to the anticipated load. Large dryers (meaning 4kW by British standards) have to have their own circuit, but most domestic types are 3kW and fitted with a regular 13A plug. That's a 3kW load that could easily be running continuously for 2 hours or more.
The washer and dishwasher elements are also generally 3kW, though obviously running for a much shorter period. But these days, people do expect to be able to run two or even all three of these appliances simultaneously, as well as using the microwave oven and kettle which are likely to be on the same circuit.
I'd like to see dedicated circuits specified for dryers, washers, and dishwashers.
David, Although subject to the same IEE Regs as us, it seems that you have certain accepted practices in Scotland which differ from those south of the border. Do you see dedicated circuits regularly for these appliances? Do you prefer to install such ccts yourself?
Trumpy, I found a ring a few weeks ago which had each end fed from a separate fuse. I'd been pulling one fuse at a time, and replacing each one as I went to identify the circuit. Of course, when the last one came out and I still had power, I started to smell rodent....
[This message has been edited by pauluk (edited 11-18-2002).]
Another nice thing can happen when lights and receptacles in one room are on different circuits. Once I had a broken light. I started to trace the fault and screwed out the fuses for the receptacle in that room. I didn't have a phase probe, only a 2 pole voltage tester, so I only checked if the receptacle was dead, which was correct. Then I started working on the switch (carefully, to my luck, not touching any bare wires). After I had put everything back together I tried the switch (sometimes the cover of such old switches blocks the switch if it doesn't sit straight, so I try them before restoring power) and was pretty surprised when I was greeted by the light of a 100W bulb. The receptacle was fed from the adjacent room and was on a different circuit. That's why I prefer having lights and power on one circuit.
I might have told you this story before, I don't remember:
Anyway: We were doing some redecoration/repainting of a room (at the engineering school) In order to do this, I took the covers off the socket outlets after having removed the fuse for the circuit. Oh yes, I checked: No voltage on the circuit.
Well, about ten minutes later I came back into the room and the lights had come back on. (People were busy working with the walls) I rushed to the fusebox angry with the idiot who had put the fuse back. The fuse was still out, where I had put it!
From the back of my head I remember that the lights were somehow connected to the outdoor security lights.
I did eventually figure out what was going on: The fool who had installed the outside security lights had put them on a randomize timer fed from a panel at the other end of the building. He had then for some reason felt it would be nice if the lights in "our" room switched on and off too. In order to achieve this, he took the live wire from the security lights outside and sneaked into a junction box in the room.
This meant that "my" circuit (and fuse box) was back-fed via the timer from another panel with separate main fuses! Real "sparky-killer"...