Motor Starter Basics

Motor Starter/Control Basics

What is a Motor Starter?

The primary purpose of a motor starter is to start and stop a motor which it is connected to safely. It is essentially a switching device.

Allows for remote operation of the motor.

Starters are made from two building blocks, contactors and overload protection: (however are commonly used with some form a circuit protection as well)

Contactors control the electric current to the motor. Their function is to repeatedly establish and interrupt an electrical power circuit.

Overload Protection protects motors from drawing too much current and overheating, from literally “burning out.”

Contactor

Functions much like a relay, in that when control voltage is applied to a coil (or electromagnet) the contacts are pulled closed allowing current to pass through the contacts to the motor. (for more information on relay operations, please click on the link in the description below.)

A magnetic contactor is operated electromechanically without manual intervention. This means that the contactor can be operated remotely, without the need for putting a person in potentially dangerous location. Magnetic contactors use a small control current to open and close the circuit.

Auxiliary contact

This can be normally or normally closed contact.

Allows us to control another circuit, which we can use to monitor the state of the contactor, and whether it is open or closed. This can also be referred to as “Run Status”

How do we protect the motor?

Starter are commonly used in conjunction with a motor circuit protector (MCP)

This is a type of circuit breaker specifically designed for motor starters, that does not utilize thermal protection.

It operates to prevent large spikes of current that could be caused by a short circuit.

It uses Magnetic protection

For more info on circuit protection, please refer to our other video.

We could use a fused disconnect switch in place of this device.

Overload Protection

What is an overload

Overloads are designed to protect against prolonged overcurrent of a motor which could cause the motor to overheat and burn up.

An overload relay consists of:

A current sensing unit (connected in the line to the motor).

A mechanism to break the circuit, either directly or indirectly.

To meet motor protection needs, overload relays have a time delay to allow harmless temporary overloads without breaking the circuit. They also have a trip capability to open the control circuit if mildly dangerous currents (that could result in motor damage) continue over a period of time. All overload relays also have some means of resetting the circuit once the overload is removed.

Review

We have a Motor Circuit Protector (this is a type of breaker that is designed for motor control)

It allows to protect the motor against short circuits, while also giving us the ability to disconnect power to the circuit if needed.

Contactor

Which gives us the ability to apply power to the motor when needed, and monitor the state of the motor (Run Status) using Aux. contacts.

Overload

Which provides the motor form sustained over current that can cause overheating.

Additional Links -

Website:
Engineering Page:
Panel Fabrication Page:
Procurement Services Page:
Manufacturers Page:
Motor & Motor Control:
Relays & Timers:
PLCs & IO:
Breakers & Fuses:
Panel Hardware:

[oooooo]

Thanks for explanation but I think it would've been better if you provided something like a visual diagram showing pointing out the parts.

[LeadSkillets]

The auxiliary contacts are also handy to create a self-latching system. Wire your NO start switch and NO aux in parallel to A1 (coil) on the contactor. Then wire a NC stop switch to A2 (coil) or through your overload aux then to A2. For a fwd/rev setup with 2 contactors, wire both A2 terminals to your NC stop switch (or through overload aux as before).

[gravityreaction]

Does the relay provide short circuit protection as well? I understand it does over current

[sarwarimam]

Very useful of contactor video..thanks of lot sir

[delavalmilker]

Some sort of animation or diagram is needed, rather than just you talking.

[bobcocampo]

Can you use overload relay for alarm only?

[Idrathernot.]

I’m trying to replace a 520F-DOD (NEMA 2 Speed Con/Var Torque Starter) with one that’s not as ancient. What product do you recommend?

[keyworksales]

You didn't put the link like you said you would :P

[nataala_]

Thank you for a great video.

I have a challenge on hand I would appreciate your assistance.

In resetting the the contactor from the overload state, must the machine be connected to mains power while the reset button is pressed and then the ON button pressed?

I am terrified of making a mistake and destroying the machine.

Many thanks in advance and once again for the training.

[김태중-ym]

his invention is such an invention that will be a milestone for the Star delta contactor. Youtube : (Amazing Contactors)

[caucasianovcharkashibainu]

Thank u for this video. I learned about contactors and there use.

[mrgreen]

Where would one find a magnetic starter? Refrigeration equipment or are we talking industrial heavy commercial equipment such as in cooling.

[sashnasiri]

Please correct the video, at 0:40 you are talking about the circuit breakers, but you say "the contactor". if it wasn't an educational video, I wouldn't put my comment.

[im-dswe]

can someone put this video into a sumerized paragraph rq for me

[buildingtechnician]

U won't even show the Motore Starter

[stepannovotny]

Brutally uninformative and simplistic video for dummies only!