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#144622 - 01/04/06 08:49 PM Ring circuits?Spur unit? RCD Device?
Rewired Offline
Member

Registered: 01/01/06
Posts: 567
Loc: Hamilton, Ontario, Canada
Hello I just have a quick question and I KNOW someone here can help me
I have always been curious as to how electrical systems and wiring methods have been done overseas, I do not know if this is still how its "Done" over there but i read that for power outlet circuits in Great Britan they are wired in a "ring".. Originating from the fuse or breaker, picking up all receptacles on that circuit and returning to that same breaker??, with the ring circuit being fused high as all the cord "caps" have individual fusing.. Is this the norm? also, I read that to "tap" off of a ring circuit you must use a device called a "spur" unit.. I am assuming this device is a form of terminal block that also contains fuses or a breaker of some sort to protect the tap or "spur"???
As well, an "RCD" or "Main RCD".. this from what I have read sounds very similar to what we use in bathroom, kitchen and outdoor receptacles as well as pool and spa circuits. a "Ground Fault Interrupter" .. whereby if 5 milliamps difference is detected between hot and neutral conductors it trips open... Is an RCD the same kind of idea only its a 33 milliamp device that is used at the main and protects the entire dwelling??
Just curious!
A.D

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#144623 - 01/05/06 12:41 AM Re: Ring circuits?Spur unit? RCD Device?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Oh No!,
Not Ring Circuits again!.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#144624 - 01/05/06 03:58 AM Re: Ring circuits?Spur unit? RCD Device?
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Ah.... The good old British ring circuit, although in my not-so-humble opinion the "good" part is highly debatable!

Yes, the ring circuit is still widely used over here. It was introduced along with the BS1363 (fused 13-amp) plug in the late 1940s.

Originally the cable size normally used was 7/.029, then with the change to metric 2.5 sq mm, which is about 20% larger than #14. Protection is then provided at the panel by a 30A fuse or C/B (32A on newer breakers).

The fuses used in the plugs are ceramic-bodied types 1-inch long by 1/4-inch diameter, available in various sizes up to 13A.

 Quote:
I read that to "tap" off of a ring circuit you must use a device called a "spur" unit.. I am assuming this device is a form of terminal block that also contains fuses or a breaker of some sort to protect the tap or "spur"???


There can be either a fused or an unfused spur. A single outlet can be run as a spur from the ring unfused. The same 2.5 sq. mm cable is usually used, which means that the 30A protection at source exceeds the rating of that spur cable. However, because all the plugs which may be connected to that spur outlet contain a fuse (max. 13A), the cable should, in theory, be protected.

The spur may be tapped from the ring either by using a regular junction box at some point, or by joining it at an existing outlet on the ring. The spur can even be wired directly fro the fuse/breaker and neutral bar at the panel.

In older installations, an unfused spur was allowed to feed two separate outlets. It was considered that diversity would prevent excess load on the spur cable.

A fused spur unit, or "fused connection unit" is used to provide a fused spur. These units take the same BS1362 fuses as are used in the plugs, and are commonly employed to feed a fixed appliance from the ring (small water heater, pump, etc.). When fitted right next to the appliance, the FCU basically just provides a hardwired equivalent to a plug-&-socket connection.

A fused spur unit can also be fitted on a ring to feed fixed wiring of a smaller size. A typical use would be to feed a few lights via a 3 or 5A fuse.

 Quote:
Is an RCD the same kind of idea only its a 33 milliamp device that is used at the main and protects the entire dwelling??


Yes, and RCD is similar in principle to a GFI. The RCD (Residual Current Device) was formerly known as an RCCB (Residual Current Circuit Breaker), and originally known as an ELCB (Earth-Leakage Circuit Breaker).

American/Canadian trip levels are used only for special locations though. In normal domestic work an RCD with 100 or 30mA trip is currently the norm. Individual breakers which combine overcurrent and RCD features for protecting a single circuit are coming into use very gradually, but a large RCD which protects either the entire installation or a part of it is the norm.

We have several different grounding arrangements in use, and where the system known as TT is employed, an RCD is essential to provide ground fault protection to the whole installation.

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#144625 - 01/05/06 04:10 AM Re: Ring circuits?Spur unit? RCD Device?
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
BS1363 outlet (single types are also available):


A standard BS1363 (13-amp) plug:


A BS1362 plug fuse:


A fused spur unit:


This spur unit has an integral switch, but they are available unswitched as well. There are also switched versions with a neon indicator.



[This message has been edited by pauluk (edited 01-05-2006).]

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#144626 - 01/05/06 03:01 PM Re: Ring circuits?Spur unit? RCD Device?
aussie240 Offline
Member

Registered: 07/06/05
Posts: 222
Loc: Blue Mountains, NSW, Australia
Paul,
What was the reasoning behind the ring circuit?
Was it to reduce voltage drop (not that that's an issue with British 200-250V mains used at the time)? Is it unique to the UK or is it used wherever British 13A sockets are used?
I did install my own 'ring main' for my 12V wiring (solar/wind charging, lead acid batteries and all of that stuff). I did this simply for reducing voltage drop. When you think about it you're getting up to twice the conductor area depending on where along the main you're drawing current and it solves the problem of the voltage drop at the last socket on the line (because there isn't one elctrically speaking).
Perhaps this technique could be of benefit to our US friends?

Trumpy,
I recall finding a book in one of our libraries concerning NZ wiring practices (this was prior to the combined AS/NZ standard). What surprised me was that mention was made of UK 13A sockets and that they were approved for use in NZ. (I know you use the British telephone socket rather than the Australian one). Is that for real and to what extent have they been used? Are they used on a ring main or just with normal AS/NZ wiring practices?

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#144627 - 01/05/06 03:25 PM Re: Ring circuits?Spur unit? RCD Device?
Wolfgang Offline
Member

Registered: 09/25/05
Posts: 154
Loc: the very West of Germany
@rings:

In Germany rings are mainly a school topic.

Except for high voltage where they are standard here.

For Europe I'd say: Ring mains are even more British than driving on the wrong side of the road. Even the Irishmen didn't really accept it. (Not quite sure regarding Malta)

Wolfgang

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#144628 - 01/06/06 01:29 AM Re: Ring circuits?Spur unit? RCD Device?
kiwi Offline
Member

Registered: 12/04/04
Posts: 347
Loc: christchurch new zealand
Aussie240, I've never seen a U.K. 13A socket in use here. If they were ever allowed here it must have been many moons ago, but I've never heard of it.

Ring circuits are good for things like outdoor floodlights and such. Where there are long cable runs.

I'm not sure if the regs here in NZ prohibit ring circuits in houses. But nobody ever installs them though.

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#144629 - 01/06/06 03:37 AM Re: Ring circuits?Spur unit? RCD Device?
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
 Quote:
What was the reasoning behind the ring circuit?


I've seen various claims and counterclaims over the years. The most usual seems to be that wiring with a ring saved materials, many of which were in short supply in immediate post-WWII Britain (even certain basic everyday items were still rationed until the early 1950s).

Prior to the ring, the standard arrangement was BS546 (unfused, round-pin) plugs and sockets rated at 2, 5 and 15A. Each 15A socket was wired on its own radial circuit back to the panel (or more likely a multitude of small 2- and 3-way units), and protected with its own 15A fuse. There would generally be a 15A outlet next to the fireplace in main living rooms for an electric heater, although they weren't always provided in bedrooms.

The 5A outlets could, according to IEE Regs., be wired three per 15A radial circuit, and were fitted in more generous quantities around the house for lower-power appliances (including smaller heaters). In practice, there were often more than three 5A sockets per circuit as wiring was extended.

The 2A sockets were intended for bedside lamps and similar and were normally wired on the lighting circuits (5A outlets could also be found on lighting ccts.).

The 13A rating of BS1363 plugs appears to have been chosen to provide for up to 3kW. Why 30A on the ring?

In the late 1940s central heating was rare. Most homes had open coal fires supplemented by individual gas or electric room heaters. My best guess is that with something in the region of 7kW to play with, it allowed the ring to supply two such 3kW loads and still leave a little room for smaller loads.

The heavy load of the ubiquitous electric kettle was almost always on the 15A (or 13A) socket provided on the cooker panel, and thus on the separate 30A cooker circuit rather than the ring. In fact in many kitchens of that time, that was the only socket!

Here are some more old threads about the ring:

Ring circuits UK style

Ring circuits revisited

Ring circuits again!

 Quote:
I've never seen a U.K. 13A socket in use here. If they were ever allowed here it must have been many moons ago, but I've never heard of it.


Mike posted a scan from some old N.Z. regs a while back which clearly shows both BS1363 and BS546 (round-pin) British outlets:

1961 Electrical Regs

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#144630 - 01/06/06 09:37 AM Re: Ring circuits?Spur unit? RCD Device?
Alan Belson Offline
Member

Registered: 03/23/05
Posts: 1801
Loc: Mayenne N. France
Wolfgang,
We, [and a few others, like Eire and Japan], don't drive on the wrong side of the road- everybody else does! The true reason was so that on horseback you could draw your sword or horse-pistol in a narrow lane and despatch a footpad or an upstart Johnny Foreigner if he turned ugly! Left handed? Hard luck! Everyone else swapped over 100 years ago for some reason. Anyway, it's too late now, all our motorways [autobahns/freeways] are built for RHD vehicles.

Alan
_________________________
Wood work but can't!

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#144631 - 01/06/06 11:49 AM Re: Ring circuits?Spur unit? RCD Device?
gideonr Offline
Member

Registered: 12/18/04
Posts: 152
Loc: Edinburgh, Scotland, UK
Never mind India, of course. About a third of the worlds population drive on the left. Anyway, end of thread hi-jack.

Rings are a more efficient use of wire, and give lower impedance and voltage drop, plus better reliability. The side benefit is that all plugs (cord caps) must be individually fused, giving more fire protection.

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