Rated voltage over 50 V requires
The protective contact pin of the plug has a larger diameter than the outer conductor and neutral conductor pins - that way it only fits into the approriate protective conductor bushing in the connector or receptacle. This specific structure and the fixed position of the protectice collar groove on the plug (must not be changed or removed) and the respective protective collar nose in the connector/receptacle prevents wrong connecting of plug and connector/receptacle and potentially fatal incidents with high voltages.
The clock position indicates the location of the prodective conductor contact on the live end of any plug or receptacle - the examplary picture above shows a connector with the clock position 6h.
The colours of a plug indicate the rated voltage. Most red plugs are made for voltages between 380 and 480 V - like the three-phase alternating current (400 V) in Germany, black plugs are designed for industries, blue plugs for household appliances, yellow plugs for safety voltage on ships and green plugs for construction machinery.
On rewirable plugs and sockets the contacts must be marked with symbols as follows:
The contact tubes of receptacles and connectors with rated voltages above 50V must be arranged clockwise as viewed from the front.
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