I have some control circuit that will open a electric gate if:

I connect GND to "open A"
or
I connect 2 - 24 volt to the base of a BC337-25 NPN

I need to add an additional switch, wich is NC, once the switch is open, it should "openA" (and keep low until switch is closed again)

 

Your transistor is drawn wrong, it has no collector supply.?

 

So if you ground "open_A" the gate opens, is that correct?

I assume sw3 is a limit switch.

If you want "open_A" low while sw3 is open, then add another transistor, with the collector in parallel with Q1 to "open_A", the emitter to GND, the base to one terminal of sw3, and the other sw3 terminal to GND.
Also connect a resistor (e.g. 10k) between the base and +24V.
Then when sw3 is open the transistor will be ON, pulling "open_A" low.
When sw3 is closed the transistor base is grounded and thus draws no collector current.

 

Your transistor is drawn wrong, it has no collector supply.?

It would appear that the "open_A" point is a pull-down signal for the gate.

 

Sorry, but the transistor, when provided with positive voltages to collector and base will be a nice and clear shortcircuit.

I cannot avoid the feeling that the OP should say what things he wants to switch with no reference to that circuit.

 

your right about the shortcut openA is either connected - SW1, or to the base of the transistor, they are not wired at the same time.


if OpenA receives GND the gate opens, it remains open untill GND to openA is released.

the Gate also opens if i put the 24v supply from the gate (also tested 3 volt from gate) to the base of the transistor.

there is a separate firealarm, with a NC contact. I want to find solution that openA opens (stay open) if NC contact is NO, or wire to firealarm NC contact is cut.

 

I want to find solution that openA opens (stay open) if NC contact is NO, or wire to firealarm NC contact is cut.

That added transistor circuit I proposed should do that.

 

Couple of things: First draw a picture of how it works now, without transistors. That way we can get a clear understanding of how the gate opener works. Second, if it works now, why do you want to put transistors in place? Or - is it NOT working now? If not - Why not?

 

Question:
Why not place SW2 in parallel with SW1 (both to ground) and eliminate the transistor for those two inputs?
You can then use the transistor for sw3 as I suggested (schematic below).

 

Thanks crutschow, I got it working, for reference this is the working schematic for me:

I deleted R1, not sure if that is okay (this is a pullup I think?)

 

So where are the other two switches?