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AnswerRelays rated for AC/DC use: the DC rating being lower than the AC, This is because DC can establish an arc across the contacts which cause the contacts to burn more,so they are rated lower.When I use relays on DC I will use double pole relays an put the contacts in series this gives a wider gap when the relay opens and helps exstinguish the arc quicker.Hope this helps.


Reply: How is putting the two sets contacts in series going to help?The same potential is still being broken at the first set of contacts.>-------------0___0--------0___0---------->Parallel would make more sense to me, since then the current would be split between the two sets of contacts.

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โˆ™ 2011-02-03 18:15:48
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Q: Why relay contact haS two different ratings for AC VOLTAGE and DC VOLTAGE?
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Overload can cause contact chatter. Once the contact closes, the voltage in the circuit collapses and that causes the relay to drop out. At this pint the relay energizes, since the voltage is back. This cycle will continue on.

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Generally speaking, a relay is an electrically operated switch. As such, there are two sets of ratings associated with a relay. The operating voltage will be specified, and the ratings of the contacts are also set down. As regards exceeding the operating voltage, this will cause excessive current to flow in the relay when it is energized. If the voltage is not significantly higher than the rating, and if the relay is not operated often or for long, it will function normally, but probably with a shorter life. At some point, excessive operating voltage will cause the coil in the relay to fail. Operating a relay to energize an electrical circuit with a higher voltage or current than the relay is designed for will shorten the life of the contacts in the relay. Higher voltage and current will quickly burn the contacts and destroy them. This is particularly true if that voltage or current is significantly higher than the ratings set by those who designed and constructed the relay. Things might work for a short time, but not for long.

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