Museum of Plugs and Sockets logo, small Maehler & Kaege
locking Garage socket and plug
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The Elektrotechnische Spezialfabrik founded by Hugo Maehler and Wilhelm Kaege in 1907 in Ingelheim am Rhein has development a large range of electrical accessories that could be used safely in spaces with an enhanced risk of fire or explosion due to flammable fumes. Arc flashes may occur when equipment is unplugged or switched off; contact with combustible material has to be avoided.
Flammable fumes could be present garages for repair or storage of motor vehicles. That explains the name Garage Steckdose und Stecker for the socket and plug shown below.


Maehler & Kaege Garage socket Maehler & Kaege Garage socket marks
Maehler & Kaege Garage plug

Maehler & Kaege Garage socket Maehler & Kaege Garage socket
Maehler & Kaege Garage socket
Maehler & Kaege Garage socket

1 - 2
Maehler & Kaege socket and plug, rated at 10A - 250V. The indication of + and -, rather than L and N suggests that primarily the device is meant for direct current*. The plug is polarized because of different pin shapes.
The earth pin (E) has a groove that allows, in combination with a turnable rod in the socket, to lock the plug. See images 3 and 4, and scheme 5 for details. A locked plug prevent unintentional disconnection of the appliance. Depending on the situation, other precautionary measures have to be taken first.
Maehler & Kaege (logo left) have outsourced Bakelite cast production to Wolff & Co. in Walsrode (MPAD mark 33-S).
Dating of the 10A Garage socket and plug: early 1930s.

* Arc formation occurs both in direct and alternating current, but it is more prominent in DC then AC. This may explain the relative low rating: 10A (DC). Plug pins and socket contacts have dimensions that would allow 16 - 20A AC.
3a- b
The large, turnable knob is a prominent socket feature. A ca. 7 cm long rod is fixed to the knob. The metal rod is ca. 2 mm thick (visible in images 3a,b) and after 90 knob rotation ca. 6 mm wide (visible in mages 4a, b).
The function of the rod is shown in figure 5.
5 Procedure to insert Maehler & Kaege plug No. 2 into socket No. 1.
The crucial element are: (i) Bakelite knob with metal rod (red), (ii) plug earth pin and (iii) socket earth contact.
Step 1: turn knob in vertical position, which corresponds to Aus position as indicated on the socket (images 3a,b).
Steps 2-4: push plug down until the earch pin touches the base of the socket earth contact (=4).
Step 5: turn knob 90 degrees (images 4a,b), which corresponds to Ein position. The bar locks the earth pin and  seures the plug. To retract the plug: turn the knob to Aus position. Note that even in an unlocked position (step 4), the earth pin is fully functional.

Garage plug locking procedure
Maehler & Kaege 6A Garage Steckdose and Stecker

6 A 6A version of the Maehler & Kaege garage plug and socket was also available. The illustration, taken from a 1929 catalog*, shows that the 6A version was nearly identical to the 10A model. The only meaningful differende refers to the shape of the minus pin: rectangular for 6A (see socket), while rectangular of 10A (see image nos, 3 and 4). This would mean that 10A plugs do not fit in a 6A socket.  * provided by Reiner Hahn.


More examples of locking plugs are shown in the museumclick here for an overview.


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