Note the following symbols.
Normally open contact symbol.
These terminals are usually labelled as normally open common and normally closed no c nc.
Also now is a good time to remind you that this is article is talking about the electrical normally open and normally closed symbols which while may look the same as the.
On off switch spst spst single pole.
Normally open contacts are designated by the lines not touching while normally closed contacts are designated with a diagonal line bridging between the two lines.
This symbol is used to indicate normally close contact.
Normally open is a contact that does not flow current in its normal state.
In a schematic diagram the switch symbol appears to be a toggle switch with a flag hanging below.
In other words when voltage is applied to the relay contactor terminals this contact closes.
Form c contacts change over or transfer contacts are composed of a normally closed contact pair and a normally open contact pair that are operated by the same device.
If we had used a normally closed pushbutton switch instead the behavior would be exactly opposite.
There is a common electrical connection between a contact of each pair that results in only three connection terminals.
Relays and contactors have two types of contacts each suited for different applications.
There is also a generic symbology for any switch contact using a pair of vertical lines to represent the contact points in a switch.
The contacts are nc normally closed and open when the back emf is high enough to pull the contacts open and take the start capacitor out of the circuit.
Normally closed nc contacts allow current through when the relay or contactor is not energized.
Normally open no contacts allow current when the relay or contactor is energized.
This is the switch used to operate a doorbell.
Push switch push to make a push switch allows current to flow only when the button is pressed.
Usually at about 75 speed of motor.
This type of push switch is normally closed on it is open off only when the button is pressed.
Normally open switch contacts are sometimes referred to in the electrical industry as form a contacts.
Like the notc contact this type of contact is normally open when the coil is unpowered de energized and closed by the application of power to the relay coil.
If the contact is normally open it would not allow any current to pass through it and hence there will be an open circuit at this contact.
Some of the most common and widely used symbols are given below 1.
Next we have the normally open timed open noto contact.
