- Wednesday, 06 February 2013 11:04
- David Savery
Have you ever sat down and considered the design delights of the humble UK plug and socket combination? No, of course you haven’t. At least, not unless you’re either a bit weird, some kind of industrial design student or me.
Okay, so the first thing to say about your standard 230V UK mains plug is that, in comparison with some foreign variants, it’s a bit big and clumsy looking. A large part of its size is due to the fact it contains room for a fuse, a necessity when hooking up sub 13A gadgets to a ring main that’s protected by a 32A breaker as you’d find in most UK homes. Most of our international neighbours lack fused plugs because their domestic distribution methods favour radial circuits with lower rated protective devices as I explain in a waffly way on my Rings n’ Radial page.
The presence of this fuse can be seen as both a godsend and a curse. A correctly rated fuse may blow under fault conditions without necessarily knocking out everything else connected to that circuit making it easy to identify which appliance is faulty while minimising inconvenience. On the other hand, when a fuse does blow, it means getting out the screwdrivers and, as BS1363 fuses all have the same dimensions, it may result in an incorrectly rated fuse being retrofitted. Worse, it may be replaced with something fire-inducingly silly like a nail or a piece of aluminium foil.
Whether you love or loathe the fuses, the fact is there are some rather nifty design features specified in BS1363, so let’s take a closer look at them for our enjoyment and entertainment!
A cord grip, where correctly fitted, will secure the cable as it enters the plug. Toothed or clamp versions are in widespread use and are equally as effective in keeping the cable in place should it be placed under strain. In the event that the cord grip is not correctly fitted, i.e. if it is missing, loose or if the outer insulation of the cable is not entering the plugtop, then it’s the line (brown) wire which is next to take the strain. Should the pull be heavy enough, this line wire will fail before either the neutral or Circuit Protective Conductor (CPC) thus ensuring the disconnection of power to whichever appliance is taking the tugging treatment. It’s a clever double line of defence to minimise potential danger caused by an overstrained cord flex.
The Circuit Protective Conductor (earth) pin is longer than the line and neutral pins by 4.6mm. This makes the CPC the first conductor to connect upon insertion of the plug into a socket outlet and the last to disconnect upon withdrawl. This design feature ensures any appliance which requires a protective earth has such in place moments before it becomes energised.
As you can see above, BS1363 plugs manufactured since 1984 are required to have insulating sleeving extending halfway up the line and neutral pins from the base of the plug to prevent accidental contact with fingers while in the process of insertion/removal or if the plug has not been fully pushed into the socket. The earth pin must not be sleeved, however cheap counterfeit imports sometimes have a sleeve halfway up the earth pin. If you come across such a plug, discard it! Read more at the PlugSafe link at the bottom of this page.
When no plug is inserted, the line and neutral socket receptacles are shuttered to prevent insertion of foreign objects. A secondary function of the longer earth pin we saw earlier is to push down on a spring-loaded lever to open the shutters allowing the line and neutral pins to enter their respective recepticles. This mechanism ensures any plug missing an earth pin cannot be inserted under normal conditions, that a plug without an earth pin cannot be inserted upside down and that little Johnny can’t stick his finger or any other foreign object into the hole and come into contact with live parts. In fact, because of these shutters there is no need to fit those child-proof plug guard things unless you have reaaalllly old non-shuttered sockets. In that eventuality, contact me and we’ll look at bringing you safely into the 21st century!
BS1363 plugs are always three pin regardless of whether a protective earth is required. They need to be as the earth pin is required to open the socket shutters covering the line and neutral receptacles. In the case of Class II appliances which don’t require an earth, a plastic earth pin may be incorporated as a shutter opening device. The three pin format and the sturdyness of these pins makes for a good hold so the plug is less likely to drop out or become loose which itself can cause arcing. The design of the plugtop is such that it can be gripped and deliberately removed with a positive pulling action while the thickness of the pins prevents them from getting bent or fractured if handled clumsily.
The three pin format also ensures correct polarisation of any appliances under normal conditions. Although many appliances are not polar sensitive and will work happily whichever way line and neutral are connected, we Brits have the advantage of knowing brown should always be (a fused) line and blue should always be a neutral - unless some dodgy DIYer has wired the sockets in your house arse about face.
So, there you go, be proud of our great British BS1363 plugs and sockets. Despite the standard being nearly seventy years old, it still makes for the safest and best designed mains outlet combination in widespread use. Little wonder then that many other countries have also adopted it.
That said, be mindful of counterfeit nasties which masquerade as being BS1363 compliant. PlugSafe have an informative page which is worth a read here.