Question for double coil DC relay

[Fotini]

Hello,can someone explain what is lagging auxiliary contact used for in DC relays(control circuit)and why is it N.C? Thanks

 

[Lucien Nunes]

Hello and welcome. A lagging N/C contact is often used on a dual-coil contactor to bypass the holding coil. The pull-in coil therefore receives the entire control voltage while the air-gap is large, the armature is accelerating and picking up the spring load of the other contacts, but once the travel is almost complete and the magnetic circuit nearly closed, the contact opens placing the two coils in series, for reduced power dissipation while held in.

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