Ladder diagram?

Because if you programmed it normally closed it would be open in the
program. :)


Is this the circuit you have?

  Start            Stop
-------[ ]----|--------[ ]------------------(out)
      out   |
-------[ ]----|-

Stop, being wired NC in the real world, is ON in the program. Start is
OFF in the program because the switch is wired NO. The OUT contact is
OFF. When you press the START button, START is anded with STOP... and
OUT comes on. Notice the OUT contact or'ed with START. When you
release START button the OUT contact keeps the circuit on until STOP
is pressed (goes "off"  in the program because now your NC switch is
open)

I had this same thought when I started in PLC's after years of relay
logic. Just look at it from the PLC input card side of things. With
the NC switch, the  STOP input point is  normally "ON".

Good luck in your new maddening career.

Steve Cothran wrote:

The STOP button in a motor-control switch box is normally closed, too.
It should be wired in series with the motor relay coil.


Indeed! from me too.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Huh shouldn't ::
  Start            Stop

  Start            Stop

or have I been missing things all these years?

jb..

It would be if your stop switch was wired normally open out in the
field, or if this was electro-mech instead of a plc.