What is the difference between relay & contactor?

What is the difference between relay & contactor?

Control Relay: It is a device through which contacts in one circuit are operated by an alteration in conditions in the same circuit or in associated circuits. Contactor: It is a device which is used for repeatedly establishing and interrupting an electric circuit under normal conditions.

What is a contactor and overload?

They consist of two main parts: Contactors and Overloads. Contactors use electrical current to operate and Overloads protect the motor from overheating.

How do you select a contactor and overload relay?

As per above chart:

1. Type of Contactor = AC7b.
2. Size of Main Contactor = 100%X Full Load Current (Line).
3. Size of Main Contactor = 100%x6 = 6 Amp.
4. Making/Breaking Capacity of Contactor = Value above Chart x Full Load Current (Line).
5. Making/Breaking Capacity of Contactor = 8×6 = 52 Amp.

When would you use a contactor instead of a relay?

Relays are used to control contacts of an electrical circuit due to a change of parameters or conditions in the same circuit or any other associated circuit. Contactors, on the other hand, are used to interrupt or establish connections in an electrical circuit repeatedly under different conditions.

Why contactor is used?

A contactor is an electrical device which is used for switching an electrical circuit on or off. These contacts are in most cases normally open and provide operating power to the load when the contactor coil is energized. Contactors are most commonly used for controlling electric motors.

What is an overload relay?

Overload relays protect the motor, motor branch circuit, and motor branch circuit components from excessive heat from the overload condition. Overload relays are part of the motor starter (assembly of contactor plus overload relay). They protect the motor by monitoring the current flowing in the circuit.

How does a contactor and overload work?

When current is too high for too long, heaters open the relay contacts carrying current to the coil of the contactor. When the contacts open, the contactor coil de-energizes, which results in an interruption of the main power to the motor.

What does AC1 mean on contactors?

AC-1 – This category applies to all AC loads where the power factor is more than 0.95. AC-3 – This category applies to squirrel cage motors with breaking during normal running of the motor. On closing, the contactor makes the inrush current, which is about 5 to 7 times the rated full load current of the motor.

How do I choose a contactor size?

1. As per above Chart.
2. Type of Contactor= AC1.
3. Making/Breaking Capacity of Contactor= Value above Chart x Full Load Current (Line).
4. Making/Breaking Capacity of Contactor=1.5×13= 19 Amp.
5. Size of Star Contactor (Starting Condition) = 33%X Full Load Current (Line).
6. Size of Star Contactor =33%x13 = 4 Amp.

Why use a contactor instead of a switch?

Why are Contactors Used? Contactors are used for high power applications. They allow a lower voltage and current to switch a much higher power circuit, so they are generally larger and more heavy-duty than control relays, enabling them to switch higher power loads on and off for many thousands of cycles (Figure 1).

What are the two basic types of contactors?

There are different types of contacts in a contactor, and they are; auxiliary contact, power contact, and contact spring. The power contact has two types that are; stationary and movable contact.

What are 2 types of overload relays?

Overload Relay Types. These are classified into two types namely thermal overload relay and magnetic overload relay.

Is a contactor required between VFD and motor?

According to some manufacturers, a contactor between VFD and motor is always a no no. The safety switch needed in many installation is usually placed bewteen VFD and motor and, in such cases, has an early opening switch that shall switch off the VFD before the main contacts open. There are many reasons for this.

What does an overload protection relay do?

A thermal overload relay is an electrical protection device designed to disconnect a machine, appliance, or installation from its power supply should damage or overload occur. This protection is achieved by the inclusion of various types of heat sensitive elements to cut the power supply under overload conditions.

What causes an electrical overload relay to trip?

The overload relay is wired in series with the motor, so the current that flows to the motor when the motor is operating also flows through the overload relay. It will trip at a certain level when there is excess current flowing through it. This causes the circuit between the motor and the power source to open.

How does the thermal overload relay work?

A thermal overload relay works on the heat produced by the excessive overload current. The heat produced by the overload current is utilized to trip the motor circuit. Sep 11 2019