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BS 1363 pin configuration
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Because of various safety considerations BS 1363 plugs are quite large. In particular size and position of the earth pin adds significantly to plug size. Opening of compulsory socket shutters by a large earth pin is a relevant safety mechanism, but it means that also class II equipment - such as cell phone, tablet and build-in laptop chargers - requires an ISOD pin (Insulated Shutter Opening Device).

Many users of portable electronic devices would like to have a compact power lead rather than a power cord with a relatively bulky standard BS 1363 plug. Several folding plug designs have been made to meet the needs of the market. Two of them have been approved, the Slimplug and ThinPlug. A third design, the Mu charger, is a folding plug with USB charger incorporated.


SlimPlug, UK-folding plug SlimPlug, UK-folding plug
SlimPlug, UK-folding plug
Drawing of Slimplug internal wiring

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Slimplug, a power lead with a folding pin plug that can be used for all equipment using a IEC 60320 C7 ('figure of eight') connector. Slimplug set a world first as it was granted a product approval license in 2006 for a folding pin plug meeting British Standard BS1363.* Plug height is 24 mm with pins closed (image nos. 1 and 2). Image no. 3 shows the plug ready for use.

To open, hold plug with pin side facing straight down and pull up on side buttons to release the pins (see green arrows in image no. 1). Let gravity do the rest. To close, place plug on a flat surface with pins upwards. Push down the side buttons to release the pins. Again, gravity will do the rest.

* The Slimplug has been designed with a view of offering a fully functional earthed plug, hence its brass earth pin. However ASTA BEAB, UK's leading independent body for electrical testing and product safety approval, has not allowed any folding plug to be earthed. The reason for this refusal is that the folding operation of L and N pins is not linked to the folding of the earth pin. L and N can be deployed whilst the earth pin remain folded, or the other way round. Both situation can be potentially unsafe. The Slimplug 'earth pin' now acts as an ISOD only.
4 Part of the original scheme showing the Slimplug internal wiring. Click for an enlargement.


ThinPlug ThinPlug

5 ThinPlug, front and side view, and IEC 60320 C7 connector. The folding plug is tested and approved by ASTA and complies to BS 1363 for class II portable electronics. The  plug is not rewirable; a figure of eight (C7) is connected to the mains lead.
The ThinPlug has a height of 16 mm with folded ISOD (image nos. 1 and 2). The red fuse holder can be rotated to replace the 3A BS 1362 fuse (see image no. 1, right).
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The central column of the ThinPlug is connected to the main body and rotates on its axis to a vertical fixed position (images 6, 7).
Then rotatably connected red pin that is housed within the central column is released and rotates into open position ready for insertion into a socket (images. 7, 8). The red pin is a ISOD. Both rotations can be done with a flick of a thumb.
To close, simply reverse the procedure.
An alternative product is the ThinCharger. It is essentially identical to the above shown model, but it has a build-in 5V-1A USB charger, rather than a mains lead and C7 connector.


empty image Mu classic USB charger
Mu classic USB charger
Mu classic USB charger

9 Mu Classic USB charger. Min-Kyu-Choi's first prototype of a folding BS 1363 mains plug, using the same principle as the Mu USB charger, was presented in 2009. The plug failed to pass the certification procedure. However, the folding USB charger does not have a mains lead and a BS 1363 certification is not necessary. The charger is on the market since 2012.
The almost square Classic charger measures 55 x 60 mm and is in closed position only 14 mm thick. The classic type has a  single, 5V-1A USB outlet.
Another type in the Mu range is the Mu Duo with two rear 5V-1.2A USB ports. There is also a more powerful Mu Tablet version that has a single 2.4A USB port.
9 - 11 Unfolding the Mu charger. Step 1: open the side flaps (images 9-10); step 2: rotate the line/neutral pins 90 clockwise (images 10-11). The side flaps are locked when the L/N pins are in horizontal position.
12 Rear view of a Mu Classic USB charger with open side flaps.


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