A motor starter is just another name for a certain type of relay that is used to control a motor. Now in the diagram below I have added a motor starter. It will continue downward as you will see later on. It's using relays to control the circuit and also the diagram will begin to take the shape of a ladder as the relay logic grows. Now these diagrams are known as relay logic or ladder diagrams. Once you let off of the STOP button the circuit is back to it's normal state with L1 waiting for the START button to be depressed. The relay contacts open to their normal state and stop the current flow to light. Now to turn the light off, you simply depress the STOP button and this will open the circuit to the relay, de-energizing the coil. Now that the contact below the START switch is closed, you can now release the START switch and the current flow goes around the open START switch, through the contact to keep the relay coil energized which also keeps the light on. This allows current flow through the contacts and energizes the light. Now the (2) MCR contacts which are normally open as shown will now close.

When the start switch is depressed, L1 now goes to the relay coil MCR (Master Control Relay) and energizes the coil. In this case L1 is hot all the way to the START switch. This means the current travels through that switch until it see's an open switch and cannot go any further. So as you can see below, L1 goes down into a normally closed switch. Just like basic house wiring, we always want to control (switch) the hot wire. Let's say were using household voltage in this circuit which is 110/120 Vac. In this example we are simply turning on a light. This diagram will show you how simple it is to control motors, lights, valves, other relays and any type load you want. See my Switch Terminology Page for more on contact arrangements if you need to.īy looking at the diagram below we can go through the basic concept of a relay and how they operate. So when wiring up these relays, the coil wire's will connect to pins 2 & 7 on the socket. As you can see, there is absolutely no difference between the square type and the round type other than the ratings on the relay. This pinout image is only a 2-pole diagram for room on the page purposes, but you can get the picture here with this one since a 3-pole will just have 1 more set of contacts. The square relay pinout shows how the relay socket is configured for wiring.

Common pin relay