Ralf That's (almost!) a perculiarly British "invention" (but also found in several ex-UK colonies/heavily-influenced countries) after" WWII to allow a larger number of sockets to be connected to a fuse (then/CB now) than can be accommodated on a branch/spur/radial circuit. This is done by running a single cable from the fuse to the 1st skt, then the 2nd and so on to the nth, and then back to the fuse again in order to save on the use of valuable copper-cored cables! It takes into account that not all skts will be fully loaded at any one time, and so the net max current is always shared between the two cables running to any one skt, under a principle called "diversity".
Might seem "unbelievable" to anyone accustomed only to branch/spur/radial circuits but it does (and has for last 60+ years) work because that is how almost all UK domestic (and probably some other) buildings are wired - IF they are installed correctly in accordance with the UK IET Wiring Regs or the national equivalent. John E Allen W. London, UK -----Original Message----- From: Ralph McDiarmid [mailto:ralph.mcdiar...@schneider-electric.com] Sent: 12 December 2016 19:34 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] British question, about a BS1363 plug-in power supply What's a "ring circuit" ? Ralph McDiarmid Product Compliance Engineering Solar Business Schneider Electric From: Richard Nute [mailto:ri...@ieee.org] Sent: Saturday, December 03, 2016 12:01 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] British question, about a BS1363 plug-in power supply I understood the fuse in the U.K. plug was to protect the power cordage. In the U.K., outlets are supplied by a ring circuit rather than a branch circuit, therefore the power cord could exceed its ampacity (a U.S.A. term). So, if no power cord, no need for a fuse in the plug. I wonder if the power supply has a fuse to protect the power supply. If so, would this count as the plug fuse? Rich From: John Woodgate [mailto:jmw1...@btinternet.com] Sent: Saturday, December 03, 2016 5:01 AM To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] British question, about a BS1363 plug-in power supply I received a 5 W SMPS plug-in power supply as part of a multi-unit product. It has interchangeable pins for EU, US, Australian and UK sockets, but it has no fuse. I think this is illegal and intend to notify Trading Standards, as the overall product is marketed by a prominent European company and is widely offered on the Internet. Is there any exemption at all for the requirement that a BS 1363 plug in any form must have a fuse? - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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