1. Standards LOW VOLTAGE Below or Equal to 1000V for AC & 1200V for DC
IS 13947
IEC 60947
Below or Equal to
1000V for AC
&
1200V for DC
LOW VOLTAGE

2. SWITCHGEAR As per IS 13947 PART I
A General term covering switching devices & their combinations with associated control, measuring, protective and regulating equipment, also assemblies of such devices and equipment with associated interconnections, accessories, enclosures and supporting structures, intended in principle for use in connection with generation, transmission, distribution & conversion of electric energy.

3. RELAY STARTER SWITCH / SD HRC FUSE SFU/FSU/SDF ACB MCCB MPCB
SWITCHGEAR
SWITCHING
PROTECTION
CONTACTOR Y N
RELAY N Y
STARTER Y Y
SWITCH / SD Y N
HRC FUSE N Y
SFU/FSU/SDF Y Y
ACB Y Y
MCCB Y Y
MPCB Y Y

4. CONTACTOR As per IS 13947 PART 4
A mechanical switching device having only one position of rest operated otherwise than by hand, capable of making, carrying and breaking currents under normal circuit condition including operating overload condition.

5. A SIMPLE ELECTROMAGNETIC SWITCH
CONTACTOR
A SIMPLE ELECTROMAGNETIC SWITCH
FOR
FREQUENT OPERATION
WITH
NO - VOLT PROTECTION
Core competency
High Operational Life

7. CONTACTOR MAIN APPLICATION AREAS
SWITCHING OF MOTORS
SWITCHING OF LIGHTING LOADS
SWITCHING OF HEATING LOADS
SWITCHING OF CAPACITORS
SWITCHING OF DC LOADS

8. SYMBOLS FOR CONTACTOR MAIN CIRCUIT

9. SYMBOLS FOR CONTACTOR AUXILIARY CIRCUIT13 21 22 14

10. LIMITS OF OPERATION Pick Up – 85% to 110% of Uc
Drop Off – 75% to 20% of Uc ( for a.c.)
75% to 10% of Uc (for d.c.)
Where Range is specified
75% & 85% shall apply to Lower Value
110%, 20% & 10% shall apply to Higher Value

11. WHY CONTACTOR ? HIGH OPERATIONAL LIFE HIGH FREQUENCY OF OPERATION
CAN BE OPERATED FROM REMOTE
CAN BE USED FOR AUTOMATIC SWITCHING OPERATIONS
CAN OFFER NO VOLT PROTECTION

12. SELECTION OF CONTACTOR
PARAMETERS
RATED OPERATIONAL VOLTAGE, Ue
RATED OPERATIONAL CURRENT, Ie
FREE AIR OR ENCLOSED THERMAL CURRENT, Ith & Ithe
UTILIZATION CATEGORY
ELECTRICAL & MECHANICAL LIFE

13. SELECTION OF CONTACTOR
PARAMETERS
RATED CONDITIONAL S/C CURRENT
FREQUENCY OF OPERATION
COIL VOLTAGES
NUMBER OF AUXILIARY CONTACTS
DIMENSIONS
TERMINAL SIZE
EASE OF MAINTENENCE
AVAILABILITY OF SPARES

14. SELECTION OF CONTACTOR
UTILISATION CATEGORIES
AC 1
AC 2
NON-INDUCTIVE / SLIGHTLY INDUCTIVE LOADS,RESISTANCE FURNACES
SLIP RING MOTORS: STARTING ,
SWITCHING OFF
AC 3
SQUIRREL CAGE MOTORS : STARTING,
SWITCHING OFF DURING RUNNING
AC 4
SQUIRREL CAGE MOTORS : STARTING,
PLUGGING & INCHING

15. UTILISATION CATEGORIES
SELECTION PARAMETERS
UTILISATION CATEGORIES
AC 5a
SWITCHING OF ELECTRIC DISCHARGE LAMP CONTROLS
AC 5b
SWITCHING OF INCANDESCENT LAMPS
SWITCHING OF TRANSFORMERS
SWITCHING OF CAPACITOR BANKS
AC 6a
AC 6b

16. VERIFICATION OF NUMBER OF ON LOAD OPERATINAL PERFORMANCE
( MAKING & BREAKING CONDITIONS ACCORDING TO UTILISATION CATEGORY )
Utilization Cat.
Make
Break
I / Ie
U / Ue
COSj
Ic / Ie
Ur / Ue
AC 1 1
0.95
AC 2
2.5
0.65
AC 3 6
0.35
0.17
AC 4
O.35

17. SELECTION PARAMETERS ELECTRICAL DURABILITY
A TYPICAL ELECTRICAL LIFE CURVE FOR UTILISATION CATEGORY AC4
NO. OF OPERATING CYCLES
OPERATING CURRENT IN AMPERES

18. ELECTRICAL LIFE IN MIXED
SELECTION PARAMETERS
ELECTRICAL LIFE IN MIXED
DUTY APPLICATION
N = A 1 + C
100 B
WHERE,
N = ELECTRICAL LIFE IN MIXED DUTY
A = ELECTRICAL LIFE IN AC 3 DUTY
B = ELECTRICAL LIFE IN AC4 DUTY
C = PERCENTAGE OF AC 4 OPERATION OF TOTAL
OPERATION

19. RELAY
A device designed to produce sudden predetermined changes in one or more electrical output circuit when certain condition are fulfilled in electrical input circuit controlling the device.

20. BIMETAL OVERLOAD RELAY
ADVANTAGES :
1. THERMAL MEMORY
2. ACCURATE PROTECTION
3. ADJUSTIBILITY
4. AMBIENT COMPENSATION
5. COMPACT CONSTRUCTION
6. LONG LIFE
7. ECONOMICAL

21. BIMETALLIC OVERLOAD RELAY
WITH DOUBLE SLIDE MECHANISM
BIMETAL
UPPER SLIDE
LEVER
STOPPER
LOWER SLIDE

24. Multiple of Set Current Trip Classes for All Relay
As per IS : Part 4
Multiple of Set Current
Trip Classes for All Relay
(Tripping Time)
1.05
≥ 2 hours
1.2
≤ 2 hours
10A 10 20 30
1.5
< 2min.
< 4min
< 8min
< 12min
7.2
2-10sec
4-10sec
6-20sec
9-30sec

25. SELECTION OF BIMETAL OVERLOAD RELAYS
FIND OUT THE NAME PLATE CURRENT OF MOTOR OR
CALCULATE THE FULL LOAD CURRENT
I FULL LOAD =
KW *
 3 * LINE VOLTAGE * COS 
SELECT SUITABLE RELAY RANGE
( ENSURE THAT FULL LOAD CURRENT OF THE
MOTOR IS TOWARDS THE MAX. RANGE OF RELAY)
ENSURE THAT RELAY TRIP CURVE IS BELOW THE
MOTOR WITH STAND CURVE ( IF AVAILABLE )

26. SETTING OF BIMETAL OVERLOAD RELAYS
FIND OUT THE NAME PLATE CURRENT OF MOTOR
MEASURE THE ACTUAL CURRENT DRAWN BY THE
MOTOR.
SET THE RELAY AS PER THE ACTUAL CURRENT
DRAWN BY THE MOTOR.
( IF THE ACTUAL CURRENT DRAWN IS MORE THAN
THE NAME PLATE CURRENT, INVESTIGATE THE
CAUSE FOR OVERLOADING )
4. IN CASE OF STAR - DELTA STARTER, CHECK UP
WHETHER RELAY IS IN LINE OR PHASE CIRCUIT.

27. SELECTION AND SETTING OF BIMETAL OVERLOAD RELAYS
( FOR MOTORS WITH LONG STARTING TIME )
IF THE STARTING TIME OF THE MOTOR IS MORE THAN THE
RELAY TRIP TIME AT STEADY STATE STARTING CURRENT,
1. SELECT A RELAY WITH DELAYED TRIPPING CHARACTERISTICS &
ENSURE THAT RELAY TRIP TIME AT STEADY STATE STARTING
CURRENT IS MORE THAN THE STARTING TIME OF THE MOTOR.
2. SET THE RELAY AS PER THE ACTUAL CURRENT DRAWN BY
THE MOTOR
NOTE : IN CASE OF MOTOR STARTING TIME BEING MORE THAN THE TRIPPING TIME OF THE RELAY EVEN FOR RELAY WITH DELAYED
TRIPPING CHARECTERISTICS AT STARTING CURRENT , BY PASS
THE RELAY DURING STARTING.

28. B A A - MAIN CONTACTOR B - BYPASS CONTACTOR
POWER WIRING DIAGRAM FOR RELAY BY PASS
R Y B B
O/L RELAY
CONTACTOR B
CONTACTOR A
A - MAIN CONTACTOR
MOTOR
B - BYPASS CONTACTOR

29. WHAT IS A MOTOR STARTER ? IT IS A COMBINATION UNIT OF
CONTACTOR (S) AND A RELAY
USED FOR SWITCHING AND
OVERLOAD PROTECTION OF
THE MOTOR.

33. FULLY AUTOMATIC STAR DELTA STARTER

34. HRC FUSE MAIN APPLICATION AREAS
AS A S.C.P.D. IN MOTOR STARTER FEEDERS
PROTECTION OF LIGHTING & HEATING CIRCUITS
PROTECTION OF TRANSFORMERS
PROTECTION OF CABLES
BACK-UP TO CBs WHERE FAULT LEVEL EXCEEDS BREAKING CAPACITY OF THE CB
PROTECTION OF SMALL LOADS ON CIRCUITS HAVING HIGH FAULT LEVELS

35. CUT SECTION OF HRC FUSE CONTACT POP UP INDICATOR HIGH RESISTANCE WIRE
BODY
QUARTZ SAND
FUSE ELEMENT

36. WHY HRC FUSE ? EXTREMELY HIGH BREAKING CAPACITY OF UP TO 100KA
VERY FAST OPERATION IN THE EVENT OF HEAVY S/C (CAN INTERRUPT EVEN IN < 5 mSEC)
CURRENT LIMITING DEVICE
- LIMITS S/C CURRENT TO A VALUE
LESS THAN PROSPECTIVE PEAK
- VERY LOW LET THRU’ ENERGY
NO MAINTENANCE REQUIRED
VERY SMALL/COMPACT SIZE
RELATIVELY LOW COST

37. LET-THROUGH ENERGY (JOULE INTEGRAL)
LET-THROUGH ENERGY = i2 dt t1
= I2 t

38. SELECTION PARAMETERS RATED POWER DISSIPATION
AS PER IS 13703/PART 2 FOR gG FUSE LINK
SIZE In MAXIMUM PERMISSIBLE
(A) POWER DISSIPATION (W)
/ /12

39. SELECTION PARAMETERS CO-ORDINATION WITH STARTER TYPE 1 CO - ORDINATION
REQUIRES THAT, UNDER SHORT-CIRCUIT CONDITIONS, THE CONTACTOR OR STARTER SHALL CAUSE NO DANGER TO PERSONS OR INSTALATION AND MAY NOT BE SUITABLE FOR FURTHER SERVICE WITHOUT REPAIR AND REPLACEMENT OF PARTS
TYPE 2 CO - ORDINATION
REQUIRES THAT, UNDER SHORT SHORT-CIRCUIT CONDITIONS, THE CONTACTOR OR STARTER SHALL CAUSE NO DANGER TO PERSONS OR INSTALLATIION AND SHALL BE SUITABLE FOR FURTHER USE. THE RISK OF CONTACT WELDING IS RECOGNIZED, IN WHICH CASE THE MANUFACTURER SHALL INDICATE THE MEASURES TO BE TAKEN AS REGARDS THE MAINTENANCE OF THE EQUIPMENT

40. SELECTION OF HRC FUSE TYPE 2 COORDINATION  1 2 3 4 5 6 7 8 9 10
TIME (SEC)
CURRENT (n  IrM) 
RELAY FUSE CONTACTOR
CH CH BR. CAPACITY
MOTOR
CURRENT
CROSS-OVER
POINT

41. SELECTION OF HRC FUSE PARAMETERS
RATED VOLTAGE
RATED CURRENT
RATED BREAKING CAPACITY
TYPE
SIZE
TIME-CURRENT CHARACTERISTICS
COORDINATION WITH STARTER
RATED POWER DISSIPATION
DISCRIMINATION WITH OTHER SCPDs

42. SWITCHES, DISCONNECTORS, SWITCH DISCONNECTOR & FUSE COMBINATION UNIT
AS PER IS (PART 3)

43. SWITCH A MECHANICAL SWITCHING DEVICE CAPABLE OF MAKING , CARRYING AND
BREAKING CURRENTS UNDER NORMAL
CONDITIONS WHICH MAY INCLUDE SPECIFIED
OPERATING OVERLOAD CONDITIONS.
SHALL BE ABLE TO CARRY FOR A
SPECIFIED TIME CURRENTS UNDER SPECIFIED
ABNORMAL CONDITIONS SUCH AS THOSE OF
SHORT CIRCUIT.

44. WHY S/W-DISCONNECTOR ?
FOR ISOLATING THE MOTOR FEEDER FOR ANY MAINTENANCE WORK
CAN BE USED AS BACK-UP SWITCHING DEVICE IN CASE OF EMERGENCIES (LIKE CONTACTOR WELDING)
POSITIVE OPENING OF MAIN CONTACTS
ADDITIONAL FACILITIES LIKE DOOR INTERLOCK & PADLOCKING

45. EQUIPMENT DEFINITION FUNCTION
MAKE - CARRY - BRAEAK ISOLATION & CARRY MAKE-CARRY- BREAK
CURRENT & ISOLATION
SWITCH DISCONNECTOR SWITCH -
DISCONNECTOR
SWITCH DISCONNECTOR SWITCH
FUSE FUSE DISCONNECTOR - FUSE
FUSE - SWITCH FUSE - DISCONNECTOR FUSE - SWITCH -
DISCONNECTOR

46. UTILIZATION CATEGORY AC20 A AC 20 B CONNECTING & DIS- CONNECTING
FREQUENT INFREQUENT TYPICAL
OPERATION OPERATION APPLICATION
AC20 A AC 20 B CONNECTING & DIS- CONNECTING
UNDER NOLOAD CONDITIONS
AC 21 A AC 21 B SWITCHING OF RESITIVE LOADS
INCLUDING MODERATE OVERLOADS
AC 22 A AC 22 B SWITCHING OF MIXED RESISTIVE
& INDUCTIVE LOADS , INCLUDING
MODERATE OVERLOADS
AC 23 A AC 23 B SWITCHING OF MOTOR OR HIGHLY
INDUCTIVE LOADS

47. Motor Protection Circuit Breakers (MPCBs)

48. ADVANTAGES : FUSELESS PROTECTION SYSTEMS WITH LOW DOWN TIME
INTEGRATED COMPREHENSIVE PROTECTION
LOWER LET THROUGH ENERGY
COMPACT
AVAILABILITY OF VARIOUS ACCESSORIES
HIGH ELECTRICAL LIFE
HIGH BREAKING CAPACITY
EASE OF CO-ORDINATION

49. Accessories with MPCB AUX. CONTACTS * INDICATE ---- ON / OFF POSITION
---- TRIP same as OFF
TRIP INDICATING AUX. CONTACTS
*S/C signaling contacts
*O/L signaling contacts
SHUNT RELEASE REMOTE TRIPPING
UNDER VOLTAGE RELEASE
DOOR COUPLING HANDLE

50. Type 2 co-ordination Application : Stand alone device
determination of cross over point
MPCB
CROSS OVER
POINT ( IN BUILT ) T I M E
MOTOR
CURRENT
5-6In
14In
CURRENT

51. MPCB SCHEME 1 MPCB PROVIDES : M
SCHEME IS RECOMMENDED WHEN SWITCHING OF MOTOR IS INFREQUENT
MPCB PROVIDES :
* PROTECTION AGAINST SHORT CIRCUIT
* PROTECTION AGAINST OVER LOAD + S/P
* SWITCHING OF MOTOR
MPCB
I>
MOTOR M

52. MPCB SCHEME 2 MPCB PROVIDES : M
SCHEME IS RECOMMENDED WHEN SWITCHING OF MOTOR IS FREQUENT
MPCB PROVIDES :
* PROTECTION AGAINST SHORT CIRCUIT
* PROTECTION AGAINST OVER LOAD + S/P
CONTACTOR IS USED FOR
*SWITCHING OF MOTOR UNDER NORMAL CONDITION
MPCB
I>
CONTACTOR
MOTOR M

53. * SWITCHING OF MOTOR UNDER NORMAL CONDITION
MPCB SCHEME 3
MPCB PROVIDES :
* PROTECTION AGAINST SHORT CIRCUIT
O/L RELAY PROVIDES :
* PROTECTION AGAINST OVER LOAD + S/P
CONTACTOR IS USED FOR
* SWITCHING OF MOTOR UNDER NORMAL CONDITION
* SWITCH OFF MOTOR ON TRIP COMMAND
FROM RELAY OUTPUT
MPCB
I>
O/L RELAY
CONTACTOR
MOTOR M