Museum of Plugs and Sockets logo, small HNA, Terko and Wieland
special purpose plugs and sockets
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HNA and Terko sockets are used in local networks, separated from a standard network sockets.  Examples are powering electronic data processing systems via a circuit that is protected against voltage spikes, situations in which interchanging live and neutral poles has to be avoided, or local networks with a different voltage or frequency.
Special, polarized connectors, made by Wieland, are shown at the bottom of page.


Terko socket Terko socket for outdoor use Terko plug Terko plug and connector

1 - 4 Terko type socket, rated at 16A-250V. Terko is a trademark of Busch-Jaeger Electro GmbH (Lüdenscheid, Germany). There are two variants, sockets with a notch near the eath contact (no. 2) and without notch (nos. 1 and 4). Each of the models in the colection that have a notch have a certain degree of protection against dust and water ingression and are more suitable for use in rough and outdoor conditions. However, the 'notch issue' is not documented in Busch-Jaeger catalogs. Terko system probably dates back to 1950s.   {ES} - nos 1 and 4;   {WN} - nos. 2 and 3


The HNA system is a German type of special plugs and sockets that exist already more tha a century.
HNA stands for Handelsschiff-Normen-Ausschuss (cargo vessel standard committee). This German shipbuilding standard dates back to 1917. The Marine-Normalien-Kommission, the navy counterpart, was established a year later.

HNA plugs and connectors are strongly made and virtually indestructible, ideal for harsh demands on board. Nowadays they are among others used on ships that carry reefer container.

A domestic version of HNA plugs and sockets have been used from early 1930s until 2010s. See nos. 5-7 below.

Merten HNA socket Merten HNA plug Merten HNA plug with cable side entry

5 - 7
HNA domestic type socket and plugs, rated at 10A-250V, made by Merten (Gummersbach, Germany). Plug no. 6 has the older Gebrüder Merten (GMG) logo, while no. 7 shows the full name of the company. Merten 2015 catalog doesn't mention HNA material anymore.
A 1930s HNA plug, made by Dr. Deisting (Kierspe, Germany) is shown on a page about classic uncommon plugs (see no. 15).
The domestic HNA variant has flat pins (2.5 x 4.8 mm). Maritime version (no. 10) has round pins. Domestic plugs have flat, rather than round pins because a KPI 1928 regulation states that "Earthed sockets are not allowed to accept unearthed plugs"
. A socket with relative narrow, flat slots cannot be used with unearthed plugs with round 4 mm pins.
Maritime and domestic HNA plugs have the same pin configuration: 19 mm L - N spacing and 10 mm earth pin offset.

WISKA HNA plug and connector

Pin confuguration of HNA plugs

WISKA HNA connector
WISKA HNA plug and connector details

8 - 12
Maritime HNA plug and connector, with round pins. Diameter is 6.0 mm for power pins and 7.5 mm for the earth pin. Plug and socket are protected against dust and water ingression according to IP56 level. Image no. 9 shows that despite a difference in pin size domestic HNA plugs (GMG, no. 6) fit in marine outlets (WISKA, no. 11).

There are two marine versions, [v.1]: 10A (DC) /16A (AC) - 150V and [v.2]: 10A (DC) / 16A (AC) - 250V. Pins have a groove and contact tubes have a pin. Position of groove and pin differ for 150 and 250 Volt. The shown plug and connector are 250V models; groove and pin are indicated with green arrows in image no. 12. The lower voltage version has groove and pin at the opposite side. HNA standard is laid down in DIN 89267 version 1 (150 Volt) and version 2 (250 Volt).

Plug and connector have been donated to the museum by WISKA Hoppmann & Mulsov GmbH in Kaltenkirchen (north of Hamburg, Germany).

Plug comparable to HNA Domestic HNA plugs closely resemble old type Israeli plugs with angled flat pins. The page on earthed sockets with similar configuration of contacts gives more information.
The Czech ČSN 35 4517 type C looks identical to HNA, but is incompatible due to small differences in pin spacing.


Wieland connectors for special use

Connectors, older type Connectors, new type Connectors, old and new type

13, 14 Male and female 16A-250V connectors, specially designed for use in cable ducts, or installations under raised floors or dropped ceilings. No. 13 is an older type, which is now replaced by the safer model no. 14. The green model has been replaced because the contacts of the outlet can be touched relatively easy with fingers or tools. The black model is better protected against direct access. Both models are polarized; L, N and earth poles are differently shaped, making exchange of line and neutral impossible.
15 Top, left: older type connector outlet and plug facing each other; top,right: connectors fully slided into one another.
Bottom, left: newer type connector partially connected; bottom, right: plug with cap removed.
Wieland Electric logo
Manufacturer of nos. 13-15: Wieland GmbH in Bamberg, Germany. A family-owned company, founded in 1910 by Fritz Wieland. Today it is a worldwide leading manufacturer of pluggable electrical installation technology.


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