why there are 2 voltages AC & DC are mentioned on the single relay ?

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why there are 2 voltages AC & DC are mentioned on the single relay ?

12 Vdc & 277Vac and something like that


thank$$$$
 

I think the 12Vdc you found on relay is the voltage required to energize the coil. The other is the one which specifies the max mains supply voltage.


Roy Vincent
 

When the relay opens it will draw an arc. The DC rating being lower than the AC because with AC power the current drops to zero 2 x f = 2 x50 (2x60) times per second (depending on 50Hz or 60Hz power), and this will allow extinguish the arc quicker. Meanwhile, working with DC power we don't get this automatic interruption and the opening arc may last longer destroying the contacts in the process. That's why relays are allowed to switch only a fraction of the AC power if DC. So that’s the reason for relay manufacturers to give us two different contact AC/ DC ratings.
 
can we use this single relay for both relay contact ratings whether AC or DC ?

Do we get 125Vac & 250 Vac output from the contacts of this relay ?
 

Look this picture ...
The principle of the relay structure

 
Above relay has one changeover switch ( Common , NC and NO )
SPDT – Single Pole Double Throw.
Of course for one switch contact voltage are the same in all three contacts

But if we take relay eg. with four switches, we can use different voltages for every switch.
( Four Pole Double Throw )

 
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How can we figure it out that which contact's voltage & amps rating is 250Vac/5A & which one is 125Vac/10A ?
Does it mention on the relay & its respective contact ?
 

How can we figure it out that which contact's voltage & amps rating is 250Vac/5A & which one is 125Vac/10A ?
Click to expand...
When there are parameters marked they are for all the contacts except for the Big or High Current Contactors where some low energy contacts are defined separately. Like in this one:

See the Datasheet for contacts specifications:
 
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