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23th June 2009


The clock in the plug

Electrical plugs and sockets for industrial use are very complicated, intended for use in difficult environmental conditions as opposed to household plugs and sockets.

Water, dust, chemicals, and special mechanical situations are the order of the day in industrial environments. Moreover, industrial plugs and sockets may be made to operate with a variety of different voltages as opposed to household sockets, which are typically adapted to 230 V.

This does not mean that they can be used for all voltages, but rather they should be used for a specific voltage only and mating a socket adapted to a particular voltage with a different voltage plug should be avoided at all costs due to the danger posed.

It goes without saying that a standard is needed, and this is fulfilled by the IEC 309, a European-wide standard that specifies the correct use of plugs and sockets.
Even Great Britain, which tends to use its own standards, has recognized the standard albeit with a few minor changes which we will not discuss at the moment.

Specifically, the IEC 60309-2 establishes standards to avoid potentially dangerous matings of plugs and sockets with different voltages.

First and foremost, each current group has a different plug and socket voltage value and also its own color code. Moreover, the ground pins in the plugs are positioned mirror opposite the ground holes in the sockets, so the plugs and sockets can only be mated if they match.

So you might be wondering what does the clock in the title of the article have to do with it?

Plenty, in fact.



RATED OPERATING VOLTAGE >50V


CLOCK DIAGRAM
Clock face position (h) of the earth pole of low voltage (>50 V) industrial plugs and sockets to IEC 60309-2 for different applications (polarity, voltage, frequency, current).
SOCKET
(front view)

Posizioni orologio - Tensioni nominali IEC

(*) Major keyway



RATED OPERATING VOLTAGE <50V


CLOCK DIAGRAM
Clock face position (h) of the minor keyway of extralow voltage (<50V) industrial plugs and sockets to IEC 309-2 for different applications (polarity,
voltage, frequency, current).

SOCKET
(front view)


(A) major keyway
(B) minor keyway

(*) No Clock face Position with Reference 24V~

Clock face position
Viewing the socket from the front, the clock
face position h is established by observing
the position of the minor keyway with respect
to the major keyway, which is always situated at 6 o’clock.
The different voltages are identified by
conventional colour codes.


Sockets with different voltages contain one or more reference marks and the contacts are specifically positioned so that they can only be mated with the appropriate plugs.

The reference marks and contact positions are indicated by the hours of the clock. The reference point corresponds to 6 o’clock when looking at the front of the plug, which is identified by the hour where the ground contact or auxiliary reference is positioned.

Next are the phases, the positive contact (if in direct current) and neutral positions.

This way we can be sure that a 16 A 3P+N+E 400V plug cannot be mated with 16A 3P+E socket.

 

Below is the standard color code:

25V
Purple
50V
White
100-130V
Yellow
200-250V
Blue
346-460V
Red
500-750V
Black

 

Lastly, the color green can be used together with those shown above when operating at frequencies higher than 60 Hz.

 


Leran more
- Institutions: IEC (International Electrotechnical Commission)
- Regulation: IEC 309-1 e IEC 309-2

 

Rev.15.0126      

 

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