|Dorman & Smith
plugs and sockets
|Dorman & Smith plugs
and sockets are
characterized by using a fuse as live pin. Patents GB566384 (appl.
date: March 23, 1943) and GB574125
(appl. date: Jan. 10, 1944) by Dorman & Smith Ltd and others
indicate that the design dates back to
1942-'43. It is not clear when production of this type of plugs and
has started; probably shortly after WW2.
Scanty information on internet suggests that D&S sockets were among others installed in prefabricated houses and council housing. D&S supplied the sockets to local authorities at low cost, with the intention of making money out of the sales of plugs, which were relatively pricey. D&S plugs and sockets gradually disappeared after the 1970s.
of two museum visitors, see Acknowledgments,
have given the possibility to show D&S plugs and sockets in full
detail. These gifts help preventing that valuable, historic devices
would sink into oblivion.
|1||Dorman & Smith socket, manufactured by Reyrolle. The Reyrolle and Company, founded by Alphonse Constant Reyrolle and based in Hebburn, Tyneside, was a large firm, specialized in development and production of switchgear and circuit breakers for power plants. After several merges it was finally acquired by Siemens. When and why Reyrolle became also involved in manufacturing D&S plugs and sockets is unclear; possibly it was related to post-WW2 years in which the company had to adapt to peace-time conditions.|
|2 - 4||D&S socket with switch. Note the D&S logo which deviates from the common (more recent ?) type; see for example plug no. 5.|
|5||Top view of a typical Dorman & Smith plug, see also plug nos. 9 and 10.|
plugs are characterized by the unique feature of using a fuse as live
pin. This design results in a more compact fused plug, compared to
BS 1363 or Wylex plugs. The orientation of pins resembles 5A BS 546
plugs, but D&S pins have a larger diameter and the offset of the
earth pin is 14.5 mm, rather than 20 mm for BS 546. The earth
pin has a groove over its full length (see image no. 12 for
Image no.7 shows the plug with the bottom half of its housing removed.
|8||Details of the fused live pin show that the fuse is screwed into the pin body. The rate of the plug simply depends on the type of fuse that is screwed in. The maximum tolerated amperage is indicate on the copper fuse/pin cap. At least 10A and 13A fuses did exist. The fundamental failing of the design is the risk that a fuse becomes unscrewed on its own in use, ending up protruding from the socket. Since the fuse is the live pin, great care has to be taken when removing the fuse, to avoid an electrical shock.|
|9||Front view of a Dorman & Smith plug showing the externally accessible screw for wiring the earth pin. D&S plugs have the earth pin accessibility in common with BS 546 plugs. Details about this feature are given at the BS 546 page.|
|10, 11||D&S type plugs. No. 10 is a genuine Dorman & Smith, while no. 11 has been manufactured by Reyrolle and Company. The shape of the safety protrusion at the side of the fuse / live pin differs between the two types (see green arrows).|
|12||D&S 2-way multi-plug.
Earth pins of D&S plugs are are 6.6 mm longer than power pins and
have a pointed tip. Length and tip ensures that the earth pin can open
the shutters by pushing a plate aside (see also inset bottom left and
image no. 14).
A groove over its full length is another characteristic of D&S earth pins. The groove is 2.8 mm wide and 1.0 mm deep. Groove and corresponding guide (see inset bottom left) ensure against attempts to open shutters with a malpositioned plug. That would result in accessible contacts because power pins are out of place. However, also the size of the duroplast base plate makes it impossible to insert an incorrect oriented plug; power pins are stopped by the base plate. That is also the case for socket nos 1, 2 and 16. Conclusion: the significance of the earth pin groove remains unclear.
|13 - 15
||D&S 2-way multi-plug which also has the functionality of a so-called piggyback, given the possibility to directly connect a cord to the plug poles. Image nos. 14 shows the compents of plug no. 14. mage no. 15 illustrates cord connection to live and neutral pins. Likewise also the earth pin can be connected to the cord.|
|16||Exploded view of a surface mount D&S socket. The collar (left) consists of two complementary halves that are fixed by screws (of which one is shown). The benefits of a two component collar is unclear. Surface mount sockets that have a single collar also exists.|
|Click for information about Wylex, another competitor of the BS 1363 standard|