DC Contactors vs. AC Contactors

A DC contactor needs to have more separation (air gap) and possibly a magnetic blow-out to interrupt the arc that forms when opening. In AC, the current passes through zero 120 times per second, which facilitates quick arc extinguisment. With DC, that doesn't happen.

jinxnao; 24 volt D.C. contractors are quieter, A.C. contractors hum after a while . pac

You are referring to the coil operation, not the switching capacity.

As well, the alloys used for DC contactor contacts have more silver in them.

so can we use dc contactors with a.c supply??

Usually yes, but you will pay more for them compared to a contactor rated for AC only.

From an electrical stansdpoint, yes. From a legal one, perhaps.

Here in my jurisdiction (Canada) you could only "legally" use a DC contactor on an AC sourse, "IF" the contactor is also rated for AC. If it is only rated for DC use then you are prohibited from using it on anything other then a DC system.

Check the legal issues where ever it is you wish to use this equipment.

Good point.