switches

if i am going to use a normally closed contact in a program to shut an output off when the switch is made, do i wire the switch normally closed or normally open? thanx.

Normally open.

You would want a high signal to shut off the coil in the software, that means a logical 1 . When the input is high so normally open contact in field.


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regards

Rheinhardt

Assuming that the program is not locked in - in other words you can change it - then decide about the external switch first. After that adjust the program as necessary. I generally try to use a normally open contact which closes when the condition I wish to sense occurs.

But in some cases the only allowed placement of the switch requires that its actuator be contacted until the motion gets to the desired point and then releases it. This type of switch would be wired Normally Closed but is Held Open (NC-HO) in its normal state. So, without further information it's impossible to tell you how to wire the switch.

In any case, in the PLC program, name the input by the condition sensed when power is applied to the input. This will help in writing the program as a NC contact (in the program) means the opposite of the lable.