ELECTRICAL INSTALLATION SYSTEMS

STAR CONNECTION A connection where three similar ends (Start or finish) of thrree phase windings are joined together to form a common point.

Any machine windings is connected in either star or delta connection

Simple operation of Limit switch

The operation of the circuit can be summarized as follows: ✅Pressing the momentary forward push button completes the circuit for the F coil, closing the normally open maintaining contact and sealing the circuit for the forward starter coil. ✅At the same instant, the normally closed interlock contact F opens to prevent the reverse direction of the motor. ✅To reverse the motor direction the operator must first press the stop button to de-energize the F coil and then press the reverse push button. ✅If the over travel position should be reached in either the forward or reverse direction, the respective N.C. limit switch will open to prevent any further travel in that direction. ✅The forward direction is also interlocked with a normally closed R contact.

Operational circuit of limit switch

A simple circuit of limit switch

✔️LIMIT SWITH Is an electromechanical device that consists of an actuator that is connected mechanically to the set of contacts. ✔️When the Object travels towards and comes in touch with the actuator, the limit switch can connect(make) or break electrical circuit. ✔️A Limit switch is used to convert mechanical motion of the objects or machines into electrical energy for various switching operation. It has two contacts states; NO and NC.

Typical set-up of contactor and overload relay

Thermal Overload relay

A simple circuit of Thermal Overload

TIMER ✔️Relay timer contains an auxiliary contacts NO and NC that can be integrated into motor control circuits. The initial state of its contact will change when activated after pre-determined value. The timer unit can be set into seconds or minutes depending on the application requirements. For longer and iterative tasks, real time timers are available

✔️STOP BUTTONA Stop button consists of a red coloured actuator, which when pressed operates a normally closed contact. On pressing the red actuator the normally closed contact will open.

✔️START BUTTON Start button consists of a green coloured actuator, which when pressed operates a normally open contact. On pressing the green actuator the normally open contact will close.

✅SWITCH Switch is an electrical device that can break and connect an electrical circuit, as well as interrupting the flow of current or divert it from one conductor to the other. ✅Types of switches typically used in motor control applications: ✅Pushbutton switch ✅Limit switch ✅Selector switch ✅Footswitch ✅Toggle switch

✔️AUXILIARY PART OF CONTACTOR. . ✅Normally Open Contact ( NO ) This is the normal state of the contact when the electromagnet ( coil ) is de-energised. This contact will close instantaneously when the electromagnet is energized. When the coil de-energised, this contact will return to its normal state i.e. open.Example of Pairs NO contacts in a contactor are 13-14,17-18, 23-24,27-28,……..57-58,63-64,67-68 ✅ Normally Closed Contact ( NC ) This is the normal state of the contact when the electromagnet is de-energised. The contact will open instantaneously when the electromagnet is energised. When the coil de-energised,the contact will return to its normal state i.e. closed. Example of NC contacts in a contactor are 11-12,15-16, 25-26,55-26,……..65-66.

✔️Auxiliary contact is the contact in the auxiliary circuit that is operated mechanically. ✔️It is physically linked to the main contacts and activate at the same time. It does not carry so much current. ✔️Auxiliary contact is also referred to as supplementary contact or control contact. ✔️It is used for auxiliary functions on a contactor, relay, or circuit-breaker. ✔️Auxiliary contact is available in various versions as normally open (NO), normally closed (NC), or changeover (C/O). ✔️It can be available internally on a device or can be mountable. Multiple auxiliary contacts can be mounted to electrical devices. ✅You can see the positions of the main contacts and auxiliary contacts of a 3-pole contactor. ✅In this example, the contactor has 3 NO Main contacts, 1 NO auxiliary contact, and 1NC auxiliary contact

When the control current energizes the operating coil of the contactor, its magnet core attracts a steel armature, the armature closes the main contacts in the the power circuits. There are compressing springs which causes the movable contacts to come back when operating coil is off. The contactor also has auxiliary contacts with normally closed contacts (NC) or normally open contacts (NO) or both placed in the control current circuits and intended to perform auxiliary control.