RC snubber placement
Quick Answer: Only Option B will &quot;protect&quot; contactor -1Q2, Option A will not limit overvoltage experienced by the contactor -1Q2.

There are several things to consider:

Placing an RC-Snubber across a contactor will provide a path for current to flow to the load, even when the contactor is off

how much current will depend on the &quot;voltage divider&quot; between the impedance @50Hz represented by your RC-Snubber and what is on the other side.


Placing the RC-Snubber across the motor, Phase and Neutral, will reduce the impedance seen by the stored energy of your transient source, that is your magnetic field in the coils of the motor. And so as the dV/dt=Z*dI/dt, the lower the Z that this transient energy source sees, the lower the overvoltage generated.

The closer you place your RC-Snubber to the element that you want to protect, the better you protect this element from surges which could potentially also come from other points in your circuit. So placing it across the contactor would be more favourable in this aspect.


In your specific case, assuming that the impedance of the grid is low and that the wires between the terminal box and your contactor do not represent a significant source of stored energy, i.e. inductance, the difference should be negligable if you place it in one place or another.
The overvoltage, which can create an arc while opening the contactor is what you want to avoid, and therefore the element of interest to protect is the contactor.
But it seems that you are worried about your hybrid starter more than the contactor.
I would suggest to place an RC snubber across the motor, phase and neutral) because I would consider more important to guarantee that a contactor does effectively cut-off the power completely to the motors.
Additionally, to limit the overvoltage on the terminals of the hybrid starter I would suggest to place some transient voltage suppression devices, such as Varistors or similar across the hybrid starter.

With regards to your drawing:
Between those two options, definetly Option B, The snubbers between your contactor -1Q2 and the motor. Option A will do nothing with regards to overvoltage experienced by contactor -1Q2.

the snubber should be placed between what you want to protect and the source of energy-transient.

Your source of energy-transient is energy stored in the coils of the motor.
The transient is created by breaking the circuit under load at the contactor and you want to limit the energy reaching the contactor by recirculating it with the snubber before it reaches the contactor.

If you attempt to recirculate it afterwards, the contactor will be exposed to the same amount of energy, besides the fact that once you manage to open the circuit, the snubber does not do anything with regards to the remainding energy inbetween the contactor and the motor because the energy cannot reach the snubber as the contactor is open.





I had not even contemplated option A because it does not allow the snubbers to work. Just for completion, these are the scenarios I had been comparing.


Other resources possibly of interest

A related Electronics StackExchange question
LittelFuse : Application Note: Inductive Load Arc Suppression
AN1048/D from On Semiconductor : RC Snubber Networks For Thyristor Power Control and Transient Suppression By George Templeton , Thyristor Applications Engineer.