Installation of float and pressure switch for motor control

[EEENGRX]

What would be the place place to install a float switch(SPDT) and a pressure switch to shut down a pump on low oil level and low pressure which would be LSL and PSL respectively considering the schematics below. I think this will be a series connection but I am thinking of installing them between the stop and start bottoms or between point 3 and M1as shown on the schematics. Let me know your thoughts and with reasons. Thanks

 

[waross]

but I am thinking of installing them between the stop and start bottoms or between point 3 and M1as shown on the schematics. Let me know your thoughts and with reasons. Thanks

Low Level Shutdown.
Between the stop and start bottoms is a good place to install the low oil level switch. That is the simplest circuit but not the best.
You may want to use the low oil level switch to activate a self latching relay that gives an indication of a low oil level shutdown.
Why? After a low oil level shutdown, enough oil may drain down to allow the pump to restart.
I would use a set of NO contacts to latch the relay and a set of NC contacts to stop the motor.
When the oil level is satisfactory, the motor may be started but the relay must be reset to clear the indicator lamp.
That said, there is nothing wrong with your intention.

Low Oil Pressure.
Between point 3 and M1; Ambiguous. There is more than one M1 device on the diagram.
Between point 2 and (A2)
OR
Between (A1) and point 3.
You will have to hold the start button down until there is sufficient oil pressure to close the switch.
In your original scheme you would never be able to start the pump.

 

[EEENGRX]

Low Level Shutdown.
Between the stop and start bottoms is a good place to install the low oil level switch. That is the simplest circuit but not the best.
You may want to use the low oil level switch to activate a self latching relay that gives an indication of a low oil level shutdown.
Why? After a low oil level shutdown, enough oil may drain down to allow the pump to restart.
I would use a set of NO contacts to latch the relay and a set of NC contacts to stop the motor.
When the oil level is satisfactory, the motor may be started but the relay must be reset to clear the indicator lamp.
That said, there is nothing wrong with your intention.

Low Oil Pressure.
Between point 3 and M1; Ambiguous. There is more than one M1 device on the diagram.
Between point 2 and (A2)
OR
Between (A1) and point 3.
You will have to hold the start button down until there is sufficient oil pressure to close the switch.
In your original scheme you would never be able to start the pump.

I intend to connect the low level float switch and the pressure switch in series.Are you suggesting not wiring them in series with each other?see both suggestions I have in the attached marked-up sheet and let me know what you think.This is because I want to attach a seal pot to the pump and I want it to shut down on low oil level and low pressure.

 

[waross]

Are you suggesting not wiring them in series with each other?

Between point 2 and (A2)
OR
Between (A1) and point 3.
You will have to hold the start button down until there is sufficient oil pressure to close the switch.

You may put them in series as described above.
Your two suggestions;
The left hand option will not stop the pump.
The right hand option, you will not be able to start the pump.
If you had an original Murphy Switch, you would be able to start the motor even with the switch in the stop circuit but:
1. I haven't seen an original Murphy Switch for decades.
2. The original Murphy Switches needed to be manually reset before each start.
The original Murphy Switch had provision to close the contacts manually. A latch would then hold the contacts closed and the motor could be started.
When the oil pressure came up, it would release the latch and the contacts would then open on falling oil pressure.
Over time, any oil pressure shut-down switch became called a Murphy Switch in some quarters.