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18th February 2009

A century of interruptions

One of the cornerstone objects of electrical plant engineering is certainly the switch.
But what were switches like a century ago?
Different and yet similar at the same time.



ScameA hundred years ago

Starting with a definition found in the 1901 Hoepli volume dedicated to lighting systems: “Switches are those devices intended to interrupt and restore the current in a circuit, in order to add (turn on) or remove (turn off) one or more lamps from the circuit”.

Despite the language, which is not very technical considering current principles, the concept is familiar.

The publication continues to list the various types (one, two and three-pole) and present the basic characteristics: “the general requirements for switches are: they must have dimensions such that they do not become heated due to the passage of the current that goes through them, nor as a result of that which may pass through them due to an abnormal event; in other words, they must have a large section and contact surface, so that the current density does not exceed 1A on the section and the contacts have a surface area of not less than 10mm² per A; they must remove the parts from contact when interrupting a circuit in a quick manner which does not produce lingering arcs between them”.



The characteristics

The publication continues: “they must be made so as to allow two positions only, closed and open, without being able to stop in intermediate positions, with imperfect contacts or with lingering arcs”.

ScameFinally, “they must be assembled on fire-proof insulating plates; the operating handles, covers and all that which may be touched must be completely insulated from parts with current passing through them".

As can be seen, nothing seems to have changed, and yet a simple physical comparison of a 1900 switch with a 2000 switch indicates many differences: shapes, sizes, materials, characteristics.

Nevertheless, some characteristics remain to represent the evolutionary lines: the safety and quality (and certainty) of the intervention.




ScameAn understandable language

Even the language has changed (and not only the market proposals in the sector, like in others).

And yet, even though a century has passed, the words and concepts expressed in 1900 are perfectly clear to us who have arrived more than a hundred years later.

A clear indication of the success of electricity.


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