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Hi, I am confused. A relay contact has a rating of 230Vac 3A, 24Vdc 3A. Does this mean that current only affects the relay contacts and voltage has nothing to do with it? Is the there no difference with the effect of 230Vac and 24Vdc? regards, paw

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In this case there appears to be no difference. However if you compared 230VAC and 230VDC, there would be a big difference. Usually DC has a larger arc when the contacts separate due to all the stored energy in the circuit. Generally speaking AC arcs quench as soon as the voltage crosses the zero point, 17ms. max. Dealing with the arc is a large factor in the contact ratings. In general terms the conducting area of the contacts relates to the current, the air gap between the contacts relates to the voltage. So voltage and current both have alot to do with it.

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thanks gerry! so the air gap distance between the contacts should be calculated with respect to the voltage to prevent current from flowing in without even closing the contacts. regards.......paw

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from a practical standpoint, you and I wouldn't ever need to calculate the air gap or the contact area. The relay designers do that for us. I don't even think those are published specs. We, as controls designers, would just select relays based on the application data (max voltage/current/contact life/etc)

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