ATS contactors sizing

[h171]

Hello

I want to use two contactors to design an automatic transfer switch (ATS) between utility and generator sources with 3X32 Amps capacity.

the load type that I will connect to the output of the ATS is lighting, heaters, Air conditioning, 1 kW water pump, and power sockets for the kitchen, laptop and etc...

for sizing the two contactors shall I do the following:

- The contactor size should be equal to or more than the 32 Amp source rating.

- shall I use a 3 or 4-pole contactor and why?

- shall I size the contactor based on the AC-1 or AC-3 rating?

could you please provide me an answer with a reference?

I really appreciate any help you can provide.

[RHH · Accepted solution]

Hello @h171 ,

Have you looked at: Discover-TransferPacT-Automatic-The-new-Generation-of-All-in-one/ Post from Schneider Electric? Some good and nice information about the automatic transfer pacts from Schneider Electric.

The questions you are asking about the poles are not really for us to answer, but for your net supplier and regulations etc.
It depends on what type of distribution system you get inside your building and what type of system you want to keep going into the building; TN-C, TN-S or TT.

If you are only talking about the contactor being 3 or 4 pole. In our country we have certain regulations regarding using contactors for by instance an emergency stop.
In this case (emergency stop) you always have to fully switch the installation off, that is including the N (Null-zero) so in that case you always need a 4 pole contactor.

Also your question related to the AC-1 or AC-3 contator and usage, I think this page might help you out with that; AC1 vs AC3 (For short reference it has to do with what kinda load you are using the contactor for, light loads or industrial loads).

Hope this has given you some valuable insight and info!

[Gregoire_Brun · Accepted solution]

Hello @h171 

completly aligned with @RHH.

Don't try to design yourself an ATS, you will take to big risk about the safety aspect. 

Our ATS garanty on eatch case of application to be safe.