what's the difference between AC and DC contactor

[erdos]

hello

I've some questions regarding contactors:

are the AC or DC referring to the control signals for the Contactors?  are these the same thing as internal coil voltage?

what are the advantages and disadvantages of one over the other?

[KeepItSimpleStupid]

There are actually two specs.

1) The coil rating
2) The AC and DC contact ratings and/or the HP (horse power) ratings

and lots more.  Some contacts on some relays can't be switched under load. 

Since this relates to switches, simple slide switches that are used for ceiling fan direction should not be switched under load.

In some cases, the ratings have to do with arc suppression. 

All of the ratings have to be adhered too.

[tautech]

And to expand a little more

Coil:
DC or AC with an AC Frequency rating, normally 50, 60 or 440 Hz.

Contacts
AC rating AND DC rating, that is usually much lower to minimise arcing and therefore meet the MTBF spec.

[Cherry]

A little understand after reading the above information.

[Pillager]

In any case, don't hook up an AC-coil-contactor to DC-voltage. Unless you wan't a smoke machine 

[woodchips]

I am still unsure as to whether the question refers to the coil or the contacts? Being that this is a contactor, not a relay, then the power being switched could be considerable. AC and DC are not the same in that case.

More details?

[Richard Crowley]

The question is to vague.  It doesn't work as a generic question.
Are you talking about the ratings of the switch contacts?  Or about the rating of the coil?

It is not a matter of "advantages" or "disadvantages".  You generally cannot use an AC-rated contactor for a DC application and vice-versa.
As others have mentioned, there are so many details missing, it is not possible to have any meaningful discussion.

[max_torque]

If we talk about the main power contacts, then an AC rated contactor can for any given size / type generally be rated to break a much higher current.
  This is because the voltage across the open contacts goes to zero during the AC cycle, which means any arcing generated as the contacts are separated when carrying a high current is extinguished in a short time.
  As the voltage across the opened DC contactor remains above zero, the arc that is generated upon opening does not stop (without other deliberately designed in "arc breaking" functionality, such as magnetic,compressed air, internal damping compounds or even explosive arc extinguishing) and hence current can continue to flow and physical damage can be caused to the contacts