We combine industrial design and technology to create some of the most reliable industrial electrical products in the world.
1. The contact of the conductor in the clamp of the plug socket-outlet.
2. and 3. The crimps at the 2 ends of the braid.
4. The contact at the socket/plug interface.
5. The conductor contact in the plug clamp.
The same care must be taken in the design and implementation of these five contacts.
The choice of contact material is fundamental. It must:
According to these criteria, the most common materials offer:
The material that best meets all the criteria is silver-nickel alloy. It is commonly used by all electrical switch manufacturers and has therefore been selected for DECONTACTOR™ to guarantee the best electrical conduction performance in operation and switching.
The force applied to the contact is a key parameter that determines the quality of a contact.
A minimum force must be applied when inserting a plug into its socket and this must remain constant over time (whether used or not).
MARECHAL® plug socket-outlets use end contacts with a spring on the socket side. The contact pressure is generated by the compression of this spring, in line with the insertion force, without any friction. This spring is very precisely calibrated and its optimum compression range is perfectly calculated.
Loose terminals (and the resulting overheating) are one of the main causes of failure. It is due to various factors:
If the terminal is fitted with a simple screw, the deformation of the copper induces a relaxation of the compression force. As a result, the contact resistance at the clamp increases and the temperature rapidly rises above an acceptable limit. Conversely, the DECONTACTOR™ is equipped with spring-lock terminals designed to compensate for the deformation (creep) of the copper and to resist shock and vibration: a constant force is applied to the conductor using a screw and a metal spring ring surrounding the body of the split terminal.
Under the pressure of the screw, the split in the terminal body opens until it is held by the ring, which then deforms elliptically and elastically. The elasticity of the ring constantly compensates for the creep of the conductor. During thermal cycles caused by the intermittent flow of current, dimensional variations are compensated for. This elastic clamping also prevents loosening due to shock and vibration. MARECHAL® appliances use different constructions based on this same principle, depending on the size of the conductors to be connected. These terminals are reusable and provide a consistent and reliable connection quality that does not require tightening checks as specified by installation and maintenance regulations.
Thermal equilibrium An appliance subject to a current flow heats up, reaching a ‘thermal equilibrium’ after a certain period of time. This stabilisation is achieved when the heat generated by the resistance of the appliance is equal to the heat dissipated along the conductors and in the environment. A conventional parameter has been defined that can accurately measure the time constant, i.e. the time for which an appliance would reach its equilibrium temperature if this rise were linear (slope) and not degressive. This period amounts to 63% of the maximum temperature rise.
Overheating By convention, temperature rises are expressed in Kelvin (K) to distinguish them from ambient temperatures in degrees Celsius or degrees Fahrenheit. The heating curve of an appliance is a function of its thermal equilibrium and its time constant. It is used to calculate its temperature rise for a given current and for a specific period.
An industrial plug socket-outlet is rarely used for stable or continuous current operation. The DECONTACTOR™ is most often subjected to much more severe operating currents of the motor start-up type, and machinery with variable consumption cycles.
The very long time constants or thermal inertia of the DECONTACTOR™ allow it to absorb current cycles without difficulty and therefore give it a long service life. The material of its contacts can withstand accidental overheating without irreversible permanent damage.
Successive temperature rise curves for a DECONTACTOR™ subjected to a particular current cycle
The IEC/EN 60309-1 plug socket-outlet standard limits contact temperature rise to 50 K in an ambient temperature of up to 45°C. Silver alloy contacts can withstand temperatures of up to 400°C without damage, and their heating is limited by the need not to damage surrounding parts or present a danger to operators. Under the test conditions specified in IEC 60309-1, the maximum temperature increase observed for MARECHAL® products is less than 50 K.
