Motor Starters
If you've taken our Relay Logic lesson, you already know how an electrical relay is used to control a circuit.
With the relay acting as the controller, we used a simple START and STOP button to control a 24 VDC motor.
This time, we have a 208 VAC motor to control!
208 VAC? These tiny relays won't work for a motor like that. Large motors and high-power systems need a device built specifically for the job: a magnetic motor starter!
Choosing a Starter
To safely control a 208 VAC motor, the motor starter must protect the motor from drawing too much electrical current and overheating. In other words it must prevent overload.
So we know we need a motor starter with components rated for 208 VAC that includes some kind of overload protection device.
A motor starter that works well for this is the WEG magnetic motor starter model ESW-B9V24-R26.
Drag your mouse over the letters below to see what each part of the model number means:
V24: Specifies the operating coil voltage, which is 208 VAC.
A: Denotes the control devices included in the enclosure, specifically the Start, Stop, and Reset buttons.
R26: The adjustable range for the 3-phase overload relay, which is 2.8 to 4.0 Amps.
Control Buttons: START (green) and STOP (red)
Reset Button
The main components of a motor starter are the the control buttons (START and STOP), the contactor, and the overload relay.
The contactor acts as our control relay, K1, while the overload relay acts as the overload protection.
Reset Button
Contactor
Overload Relay
In later lessons we will dive into the intricate mechanisms of the contactor and overload relay. Here we will be looking at how these components work on a system level.
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