On Thu, 13 Aug 2020 05:52:00 -0700 (PDT), "
wrote:

Why isn't the switch at the pump? How are you going to get power from the house to the pump, without new a new power line?

After all this confusion - I expect that the OP means to "control" the pump from the house. If I can interpret the issue (risky, always).
a) The house has a back-up generator.
b) The line to the pump is from the house, but the power to the tank is from the shop, not backed up.
c) The pressure switch is at the tank.

I interpret this to mean that a 120V pressure-switch is controlling a 240V pump, powered by two different sources. Which is flat-out nuts.

I am interpreting (again, risky) that the OP wants the controls at the pump.

So, the 120V source at the shop will control a 240V (hopefully) contactor at the pump.

All the while forgetting that if there is a power-failure, that 120V source will be dead - so, no water.

Clue 1: The tank does not care where it is in the system.
Clue 2: The tank will be perfectly happy staying where it is, with all controls, pressure-switch, contactor and so forth at the pump - in suitable enclosures, of course.

Peter Wieck
Melrose Park, PA
The tank and pressure switch are at the shop and have been so for
over 20 years. The pressure switch has two contacts. The 240 volt
power from the shop, where the tank and pressure switch are, is
switched by the pressure switch. The pressure switch has a completely
mechanical action. The pressure switch switches both legs of the 240
volt power.
When the house was built and I was digging ditches I put conduit in
the ground from the house to the well so that I could eventually power
the well from the house.
Now that I have the generator panel and transfer switch installed
and bought off at the house I want to power the well from the house so
that the generator will be able to power the well when the power goes
out.
I pulled wire from the house to the well to supply power, so now
power from the house is at the well head.
The pressure switch must be located at the pressure tank for proper
operation.
I am not going to move the pressure tank.
So all I want to do is to use the existing pressure switch to
switch the power to a contactor coil. The power for the contactor
coil that the pressure switch will be switching will be coming from
the house. The contactor will be switching the power coming from the
house. There will no longer be any power coming from the shop. Nowhere
did I say any switch was 120 volts. What is wrong with doing this?
Eric