環形電路何時出現和是誰發明?

The ring circuit and the associated BS 1363 plug and socket system were developed in Britain during 1942–1947. They are commonly used in the United Kingdom and to a lesser extent in the Republic of Ireland. It is likely that they are also used in parts of the Commonwealth of Nations, where Britain had design influence in the past.

The ring main came about because Britain had to embark on a massive rebuilding programme following World War II. There was an acute shortage of copper, and it was necessary to devise a scheme that used less copper than would normally be the case. The scheme was specified to use 13 A fused socket outlets, and several designs for the plugs and sockets appeared. Only the square pin (BS 1363) system survives, but the round pin Dorman & Smith system was still in use in many locations well into the 1980s. This latter plug had the distinctive feature that the fuse was also the live pin and unscrewed from the plug body.

The ring circuit was devised during a time of copper shortage to allow two 3 kW heaters to be used in any two locations and to allow some power to small appliances, and to keep total copper use low. It has stayed the most common circuit configuration in the UK, although the 20 A radial (essentially breaking each ring in half and putting the halves on a separate breaker) is becoming more common. Splitting a ring into two 20 A radials can be a useful technique where one leg of the ring is damaged and cannot easily be replaced.

Another advantage of ring circuits was an economy of cable and labour, as one could connect a cable between two existing 15 A radially wired sockets to make one 30 A ring, then adding as many sockets as were desired. This was an important consideration in the austerity of the 1940s. This would leave the ring supplied by two 15 A fuses, which worked well enough in practice, even if unconventional.



2010-02-23 23:54:24 補充：
Many pre-war (round pin) installations used double pole fusing. When two 15 A radials were converted to a ring on these systems, the ring would then be supplied by no fewer than 4 fuses. Such circuits are rare today.

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環形電路 ：活線、中線和地線各自形成一個環形線路，而市電電路則從支線供電。



環形電路的優點是電流從兩個不同路徑到達每一個插座，所以即使採用較幼的電線也不會過熱。



所有插座都以並聯的形式直接連接到環形電路，如果一個插座壞了，其它插座仍可運作。



在環形電路中，每條電線所負荷的最大電流只是整個環形電路的一半。因此，可用較細和較便宜的電線。同時，由於所有插座都是並聯的，所以連接到插座的電器都可以獨立地以220 V操作。