Museum of Plugs and Sockets logo, small Czech Republic and Slovakia
three phase plugs
navigation icon navigation icon navigation icon


Until the 1990s 16A and 25A three-phase plugs, characterized by a row of four or five flat pins, were commonly used in Czechoslovakia. The type, known as Flako (German abbreviation of Flach Kontakt) was used also in Austria, Germany, Netherlands and Poland.
From the 1990s Czech and Slovakian electro-technical companies switched to IEC 60309 three-phase plugs and sockets, but for some time a limited production of 16A Flako plugs continued to support older facilities. Plugs shown in image nos 1-3 are examples of the last production series.


4-pin Flako-type plug made by Elektro-Praga

      SEZ logo
4 and 5-pin Flako-type plugs made by Elektro-Praga 5-pin Flako-type plug made by Elektro-Praga

1 16A - 380V three-phase plug, without Neutral contact. Model no. 3632-20*. It is not indicated which of the three shorter pins is L1, L2 and L3 (previously designated respectively R, S and T). Pin sizes are listed in the table below.   {FSE}
2 Comparison of 16A plugs with and without Neutral contact. Although plug and pin sizes are largely identical, a 4-pin plug does not fit in a 5-pin socket, because 4-pin plugs have two grooves and 5-pin plugs have 3 grooves. Sockets have corresponding ridges (see image 4).
3 16A - 380V three-phase plug with Neutral contact. Model no. 3632-40*. The red arrow probably points to the Neutral contact (see image 5). Pin sizes are listed in the table below.   {FSE}
* Plug nos 1 and 3 have the characteristic triangular logo used by the Czech company Elektro-Praga. Plugs have been donated by Spezialelectric in Ludwigsburg, Germany. A note was added to plug no. 1, stating that the plug was bought from SEZ (Slovenské Elektrotechnické Závody) in Dolný Kubín, Slovakia; a company that once belonged to the state-owned group of electro-technical companies managed by Elektro-Praga. In 1970 SEZ separated from Elektro-Praga, but the SEZ logo still carries the triangular logo.


Examples of flat pin plugs made by companies in other countries

4-pin Flako-type plug made by Ospel
4-pin Flako-type plug made by Hazemeyer Hengelo

4 25A - 380V 3-phase + earth, 4-pin plug and matching socket, made by the Polish company Ospel.
Overall size of the 25A plug and pins are approximately 15% larger than the 16A model shown in image no. 1.
5 15A - 380V 3-phase + N + earth, 5-pin plug, made by the Dutch company Hazemeyer in Hengelo (HH).
Plug and pin sizes are essentially identical to the 16A model shown in image no. 3.


pin sizes

Pin sizes of Elektro-Praga / SEZ 16A 3-phase plugs shown in image nos 1 (4-pin) and 3 (5-pin).

a: length
b: width
c: thickness
d: pin spacing

4-pin plug (3632-20)

5-pin plug (3632-40)
sizes in mm
L pins
earth pin

L pins N pin earth pin
length (a)

width (b)

thickness (c)

pin spacing
13.0  /  26.0  /  13.0

13.0  /  13.0  /  13.0  /  13.0


Navigation icon D i g i t a l   M u s e u m   o f Navigation icon P l u g s   a n d   S o c k e t s Navigation icon