Transcript:
[0m:00s] Hey, I'm Mitchell. Welcome to another video in the RSP education series. Think a basic motor starter is all you need? Think again. When you're dealing with direction control, massive inrush currents, or delicate mechanical systems, a plain old direct over-the-line starter won't cut it. In this video, we're going to walk through three advanced motor starter types: reversing, star-delta, and soft starters, and show you how they give you smarter, safer, and more precise control over your motors. Pro tip: contactors are not meant to interrupt short circuits. You still need a circuit breaker or fuse for that. Contactors are just the on and off gatekeepers for motors. If you like this kind of content and want more educational videos, please like and subscribe. Also, this video is for educational purposes only. Consult a professional for your application. RSP Supply is not liable for any misuse of this information. With that said, let's dive in.
[1m:01s] So, types of starters beyond DOL. You've already got the basic starter equals contactor plus overload relay concept understood. But to go deeper, reversing starters. A reversing starter is basically two contactors wired in a special way so you can change the direction a motor spins, like forward and reverse. The way it works is motors, especially three-phase ones, change direction if you swap two of the power wires or phases. A reversing starter has two contactors—one wired for forward, one wired for reverse. When you hit forward, one contactor closes. When you hit reverse, the other contactor closes and it swaps two phases to reverse the spin.
[1m:47s] A key detail is interlocking. You never want both contactors to close or be energized at once. That would short two phases together, possibly damaging your motor or contactor. That's why we use electrical and mechanical interlocking. Electrical interlock uses control circuit logic that disables one if the other is running. Mechanical interlock is simpler—a physical piece that prevents both contactors from moving at the same time. These are used in conveyors that need to reverse, hoists, cranes, or any equipment where direction matters.
[2m:22s] Now, star-delta starters. These help reduce high inrush current during motor startup. Especially for bigger motors, this is important because when large motors start, they draw a lot of current—sometimes six to eight times higher than normal. This can trip breakers, dim lights, and stress the power grid. The way star-delta works is that when starting, the motor is wired in a star configuration, which reduces the voltage and current going to each winding. After a few seconds, the circuit automatically switches to a delta configuration, giving full line voltage for normal operation. Inside the star-delta starter are usually three contactors. The first is the main, which turns the motor on. Then there's the star, which connects windings in star, and the delta, which reconnects them in delta. A timer or PLC controls the switch from star to delta. These are used in large pumps, fans, compressors, and motors over 15 kilowatts or 20 horsepower typically, especially in older or cost-sensitive setups.
[3m:26s] Soft starters. This is a solid-state device that uses electronics, not moving parts, to gently ramp up motor speed by slowly increasing voltage. We've talked about these before because motors normally slam on instantly at full voltage. This causes torque shock, belt slippage, or water hammer in pipelines. Soft starters, on the other hand, let the motor ease in smoothly, then bypass themselves once full speed is reached. These work using thyristors or SCRs—power electronics that control the voltage going to the motor. You can program it to ramp up over a few seconds, like five. Does it replace a contactor? Not really. You still often need a bypass contactor to take over once the motor is running for less heat and better efficiency. You may also use a contactor for isolation or emergency stop. These are used in pumps, conveyors, HVAC systems, and blowers—anywhere smooth starts matter.
[4m:25s] To wrap up, reversing starters give you directional control with built-in interlocks for safety. Star-delta starters reduce brutal inrush current during motor startup for more cost-sensitive applications, and soft starters bring a smooth, gradual ramp-up that protects your equipment. Each one solves a unique challenge, and knowing when and why to use them gives you serious power in motor control design. So don't stop at DOL—level up your starter game. For contactor options and hundreds of thousands of other industrial automation products, please visit our website at rspsupply.com, the internet’s top source for industrial hardware.