Normally open (NC) contact concept.

Normally open (NC) contact concept.

This is PLC Program for NC contact.

Normally closed contact is known as NC contact. When the quantity has signal state 0, the NC contact allow signal flow and output result is 1.

When the quantity has signal state 1, the closed contact is not activated and therefore output state is zero.

If two NC contacts are connected in series, the power flows once all contacts have zero signal state.

If two NC contacts are connected in parallel connection, the power flows when one NC contact amongst all have zero signal state.

Example of the NC contacts.

In above example two NC contact are connected in series (tag 1 and tag 3). When both signal state are zero, output result is 1.