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I need help with a control wiring circuit (exam)

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New Member
Here's the summary:

- A push button is used to start a supply fan (controller 1).
- A return fan (controller 2) is interlocked to start automatically with the supply fan.
- In the event of a smoke condition the fans shutdown automatically.
- The supply and return fans cannot be restarted until the smoke detector system is reset (a latching relay is going to be used).
- In the case of excessive smoke, an exhaust fan (controller 3) can be started but only if the smoke detector system has not been reset.

A need to create a ladder and wire diagram.

I'm having problems from the third step down.


New Member
I tried to post a diagram of what I had so far but it didn't go through.

I'm having problems setting up the latching relay and the exhaust fan.


You mention that you have to create a ladder and wire diagram.

Are you going to use a PLC programmed in ladder logic or are you going to do the assignment with relays, hence the need for wire diagram?

If using a PLC, surely there should be some SR (Set/Reset) flip flop software elements in the application? If using relays, latching relays are available (relays with a Set coil and a Reset coil)
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