How can I protect of output of relay (PLCs or some relay)

I khow that I can protect a contact of relay by using- varistor/diods.
There is output of PLC that is contact of relay. There is 48VAC 50Hz. Max 2Amper of load. Could you suggest me what type/mark of varistor can I use for protect these ones?
Thanks in advance....

P.S. I found type of varistor-
B72210-S 750-K101,S10K75 10J 75v
B72520-V 600-K62,CN1206K60G 0.9J60v

Hi Valera,

for relay contacts on AC load you cannot use (freewheeling) diodes. These are for DC loads only.

You can use varistors or RC buffers. RC buffers are better.
As these typically (but not allways) snap directly into a socket on the contactor you must check with the make of the contactors you have. In the catalog there should be some varistors or RC buffers for the contactors with 48VAC coils.

I know that i must use varistors for AC circuit. "B72210-S 750-K101,S10K75 10J 75v " is exactly one. But I dont't know what exactly type of varistor I can use for for example->
There is PLC output that is contact of relay. And there is the load for this output. Load is contactor- ABB AE9-30-00 supply for coil is 48VAC.
What type of varistor can I use?? May be you look for yours applications and check type of varistors that is attach to yours coil, contactors e.t.c....
Thanks for advance.....

Valera,

the answer is that there is a varistor specifically made for that ABB contactor (*). It snaps right into the contactor itself.
You have to look into the ABB contactor catalog to find it.
I dont use ABB so you have to do it yourself.

An alternative is to wire a separate varistor over the contactor coil.
This doesnt have to be an ABB type. You just have to match voltage and wattage of the varistor with the coil. But this is cumbersome, the snap-in type is much easier.

*: I assume that it is a new and modern type contactor, and that it it isnt a very large size. Extra large size contactors sometimes have separate rather than snap-in type suppressor units.

It is almoust what I want to know. There is item of description of varistor-> average dissipated power. It must be equal to power of coil.Is not it? Am I right?

No,
the varistor only gets loaded with a short impulse of energy when the contactor is deactivated.
The contactor coil rating is the constant power required to hold the contactor activated.

Not sure what "average dissipated power" means. It could be a rating of how much power it can continously dissipate before breaking down.

edit: If you get the combination of varistor and contactor from the catalogue, then you cant go wrong.

JesperMP wrote: If you get the combination of varistor and contactor from the catalogue, then you cant go wrong.

I know it, but I think that this varistor (from combination of catalogue) is very expensive. Cost of varistor that I see in shop is 0.2$USA.

Buy one and try it out.
If the varistor is physically large, then it can handle the load of the deactivating coil.
Think that the varistor inside the snap-in block is physically smaller, and that the rating of the varistor follows the size.