Guide to Electrical Contactor and Relays

Electrical ContactorElectrical Contactor and Electrical relays are widely used for the electrical controlling circuits. Main purposes of these electrical controlling circuits are control larger electrical device such as motors, generators ect. An Electrical contractor is an electro-magnetic switching device used for remotely switching a power or control circuit.When a relay is used to switch a large amount of electrical power through its contacts, it is designated by a special name called as contactor.

Type of Points in Electrical Contactors

A contractor is a very heavy-duty relay used for switching electric motors and lighting loads. High-current contacts are made with alloys containing silver. Normally contractors have two points.

  1. Normally Open Points
  2. Normally Closed Points

Most common industrial use for contractors is the control of electric motors.Such devices are often used for motor starters.Large electric motors can be protected from over current damage through the use of overload heaters and overload contacts.

We can add some auxiliary contact points in to these contractors too.

Electrical Contactors

Electrical Contactors are one of the most widely used electrical equipment’s in electrical controlling engineering. Following are several methods which use to control the electrical contactors using the signals.

•    Control a high-voltage circuit with a low-voltage signal
•    Control a high-current circuit with a low-current signal
•    Detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers

A relay is an electrically operated switch.

Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts.

The coil current can be on or off so relays have two switch positions and they are double throw changeover switches.

The relay’s switch connections are usually labeled as COM, NC and NO. normally I have saw 8 pin relays and those are connected to the relay base.

COM = Common, always connect to this; it is the moving part of the switch.
NC = Normally Closed, COM is connected to this when the relay coil is off.
NO = Normally Open, COM is connected to this when the relay coil is on.

Time Delay Relays

this is control relay with time delay and the main objective is to control relay on time basis.

Time-delay relays can be constructed to delay armature motion on coil energization, de-energization, or both. Relays can be modified to delay opening or delay closing a set of contacts.

A very short delay. Current flowing in the disk maintains the magnetic field for a short time, lengthening release time.

For a slightly longer (up to a minute) delay, a dash pot is used. Time-delay relays can be classified as

  • On delay Timer
  •  Off delay Timers Normally Time delay relays are working under two conditions such as
    1. The voltage apply for the device or TDR (Known as Power Trigger)
    2. Opening or Closing trigger signal from the device.

Normally most of electrical relays are specially make by shock absorbing feature.

Unlike electrical contactor which we discussed above time delay relays nor not kind of normally open or normally closed type but the time delay operate in the area of closing and opening.

There are other types of relays are also use in different application in electrical industry such as protective relays, solid state relays. Features and applications of these relays are change in the way of Time Delay Relays and Electrical Contactors.

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