Spdt Relay Switch Diagram. So basically you can see the spdt relay as a way of switching between 2 circuits. Dp switches control two independent circuits and act like two identical switches that are mechanically linked.
One can be normally closed and the other one is opened or it can be normally open and the other one closed. The red led now shuts off and the green led turns on. The single pole double throw spdt relay is quite useful in certain applications because of its internal configuration.
As you can see the coil is an electromagnet that causes the arm that is always connected to the common 30 to pivot when energized whereby contact is broken from the normally closed terminal 87a and made with the normally open terminal 87.
One can be normally closed and the other one is opened or it can be normally open and the other one closed. The single pole double throw spdt relay is quite useful in certain applications because of its internal configuration. It has one common terminal and 2 contacts in 2 different configurations. The diagram below figure 2 shows an spdt relay at rest with the coil not energized.
