MCB / MCCB / ELCB Quick Reference (Part-2)

 

Selection of MCB
MCB curve	Type of Load	Residential	Commercial
B curve	Resistive Loads	Incandescent lights	Incandescent lights
		Geyser	Boilers
		Heater	Heaters
		Fan blower heaters	Oil radiator heaters
	Slight Inductive Loads	Florescent Lights	Florescent lights
		Small motors (FHP)	High pressure mercury vapor lamps
C curve	Slight Inductive Loads	Fans & small pumps	Sodium vapor lamps
		Window / Split ACs
		Lights with ballasts
		Microwave
		Refrigerators
		General household equipment
D curve	Inductive Loads	Water lifting pumps	Florescent lights
		UPS	ID & FD fans
			Small control transformers
			Medium size motors
			Refrigerators for commercial use

 

Type of MCB
MCB Curve	Type of Load	Response	Tripping	Application	Uses
B curve	Resistive loads	MCBs react quickly to overloads	3 To 5 times F.L current (0.04 To 13 Sec)	Domestic & Commercial applications	Suitable for incandescent lighting, socket-outlet, bulbs, heaters etc. Protection of DG sets (since DG sets have low short-circuit capacity)
C curve	Slightly inductive loads	MCBs react more slowly,	5 To 10 times F.L current  (0.04 To 5 Sec)	Commercial and Industrial applications	Highly Inductive loads such as motors, air conditioners, fluorescent lighting lights, fans & household electrical appliances.
D curve	Inductive loads	MCBs are slower	10 To 20 times F.L current  (0.04 To 3 Sec)	Commercial and Industrial applications	Very high inrush Inductive currents, Small transformers, welding machines. UPS, small motor & pumps, x-ray machines etc. Note, however, that MCBs with Type K characteristics may provide better protection in some applications of this type.
K curve	Inductive loads	MCBs are slower	8 To 10 times F.L current  (0.04 To 3 Sec)		Placing them between the traditional Type C and Type D breakers. In most cases, they allow improved cable protection to be provided in circuits that include motors, capacitors and transformers, where it would previously have been necessary to use Type D devices. This enhanced protection is achieved without increasing the risk of nuisance tripping.

 

Selection of RCCB
Type of RCCB	Sensitive	Application
Type AC	Sensitive to AC Currents Only	Suitable for most domestic and commercial applications.
Type A	Sensitive to AC Currents + Pulsating DC Currents (Produced by Rectifier, Thyristors)	Used where there are a lot of “electronic” loads, such as computer equipment or lighting systems with electronic ballasts.
Type B	Sensitive to AC Currents + Pulsating DC Currents+ Pure DC Currents	Use in photovoltaic (PV) solar energy installations because the PV panels produce a DC Output and some types of fault can result in the leakage of DC Currents to Earth.
Type B+	Similar to Type B, but respond to ac leakage currents over a wider frequency range	Type B and Type B+ devices can be used wherever a Type AC or Type A device is specified, as they provide the same functionality as these types and more.

 

TYPE of RCCB
TYPE	AC Current 50Hz	AC Current 50Hz To 1KHZ	Pulsating Current with DC Component	Multi Frequency Current Generated By 1Phase Inverter	Multi Frequency Current Generated By 3Phase Inverter
AC	√	–	–	–	–
A	√	–	√	–	–
F	√	–	√	√	–
B	√	√	√	√	√
AS	√	–	√	–	–
BS	√	√	√	√	√

 

Sensitivity of RCCB
RCCBs	Application
30 mA	personal protection domestic installation / direct contact
100 mA	limited personal protection / indirect contact
300 mA	building / fire protection

 

MCB Enclosure Size
MCB Rating (A)	Min. Enclosure Size
	Height	Width	Depth
100A	370mm	216mm	72mm
125A	310mm	180mm	83mm
225A	370mm	217mm	72mm
250A	380mm	195mm	83.5mm
300A to 400A	506mm	381mm	153mm
600A to 800A	520mm	420mm	200mm
1000A to 1200A	704mm	554mm	173mm
1600A to 3000A	1016mm	608mm	615mm

 

Switch Gear Protection
Switch Gear	Protection		Isolation	Control
	Over Load	Short Circuit
Fuse	YES	YES	NO	NO
Switch	NO	NO	YES	YES
Circuit Breaker	YES	YES	YES	YES
Contactor	NO	NO	NO	YES
Disconnector	NO	NO	YES	NO

 

Type of Faults
Types of Fault	Reason	Consequences	Protective Device to be used
Overload	When Equipment tries to run beyond its rated capacity, or there is a fault in the equipment E.g. When you keep a heater on without any water in it.	It can lead to reduction in life of equipment, Failure of insulation and hence damaging the equipment.	MCB / RCBO
Short Circuit	Insulation Failure, Shorting of the Phase to Phase or Phase and Neutral Wires.	High Inrush Current, causing permanent damage to equipment and may lead to a Fire.	MCB
Earth Fault	Short circuit between Phase and Earth Conductor.	Can result in Fire due to sparking.	RCBO / RCCB
Earth Leakage	Human Body Touching Live Wires. Insulation failure		RCBO / RCCB
Over Voltage	Opening of Neutral Connection increase in Phase To Phase Voltage of 440V, Surge through Lighting or transients, Over voltage from Utility.	Damage to sensitive Electronic Equipment.	OV protection Device
Under Voltage	Drop in supply voltage, starting of heavy loads	Damage of Equipment, Flickering of Lights.	UV relays

 

MCB Type (BS EN 60898-2)
Trip Type	instantaneous Trip (< 0.1 s)	Load Type	Typical Load
B	3 to 5 In (AC)	Resistive	Heaters, showers, cookers, socket outlets.
	4 to 7 In (DC)
C	5 to 10 In (AC)	Inductive	Motors, general lighting circuits, power supplies.
	7 to 15 In (DC)
D	10 to 20 In	High Inductive	Transformers, motors, discharge lighting circuits, computers

 

Relays for Transformer
Capacity of Transformer	Relays on HV Side	Relays on LV Side	Common Relays
Generator Transformer	3 Nos Non-Directional O/L Relay	– –	Differential Relay or
	1 no Non-Directional E/L Relay		Overall differential Relay
	and/or standby E/F + REF Relay		Over flux Relay
			Buchholz Relay
			OLTC Buchholz Relay
			PRV Relay
			OT Trip Relay
			WT Trip Relay
220 /6.6KV Station Transformer	3 Nos Non-Directional O/L Relay	3 Nos Non-Directional O/L Relay	Differential Relay
	1 no Non-Directional E/L Relay		Over flux Relay
	and/or standby E/F + REF Relay		Buchholz Relay
			OLTC Buchholz Relay
			PRV Relay
			OT Trip Relay
			WT Trip Relay
132/33/11KV up to 8 MVA	3 Nos O/L Relay	2 Nos O/L Relays	Buchholz Relay
	1 no E/L Relay	1 no E/L Relay	OLTC Buchholz Relay
			PRV Relay
			OT Trip Relay
			WT Trip Relay
132/33/11KV up to 8 MVA to 31.5 MVA	3 Nos O/L Relay	3 Nos O/L Relay	Differential Relay
	1 no Directional E/L Relay	1 no E/L Relay	Buchholz Relay
			OLTC Buchholz Relay
			PRV Relay
			OT Trip Relay
			WT Trip Relay
132/33KV, 31.5 MVA & above	3 Nos O/L Relay	3 Nos O/L Relay	Differential Relay
	1 no Directional E/L Relay	1 no E/L Relay	Over flux Relay
			Buchholz Relay
			OLTC Buchholz Relay
			PRV Relay
			OT Trip Relay
			WT Trip Relay
220/33 KV, 31.5MVA & 50MVA , 220/132KV, 100 MVA	3 No O/L Relay	3 Nos O/L Relay	Differential Relay
	1 no Directional E/L Relay	1 no Directional E/L Relay	Over flux Relay
			Buchholz Relay
			OLTC Buchholz Relay
			PRV Relay
			OT Trip Relay
			WT Trip Relay
400/220KV 315MVA	3 Nos Directional O/L Relay	3 Nos Directional O/L Relay	Differential Relay
	1 no Directional E/L relay.	1 no Directional E/L relay.	Over flux Relay
	Restricted E/F relay	Restricted E/F relay	Buchholz Relay
	3 Nos Directional O/L Relay for action		OLTC Buchholz Relay
			PRV Relay
			OT Trip Relay
			WT Trip Relay
			Over Load (Alarm) Relay

 

Relays for Transmission & Distribution Lines Protection
Lines to be protected	Relays to be used
400 KV Transmission Line	Main-I: Non switched or Numerical Distance Scheme
	Main-II: Non switched or Numerical Distance Scheme
220 KV Transmission Line	Main-I : Non switched distance scheme (Fed from Bus PTs)
	Main-II: Switched distance scheme (Fed from line CVTs)
	With a changeover facility from bus PT to line CVT and vice-versa.
132 KV Transmission Line	Main Protection : Switched distance scheme (fed from bus PT).
	Backup Protection: 3 Nos. directional IDMT O/L Relays and
	1 No. Directional IDMT E/L relay.
33 KV lines Transmission Line	Non-directional IDMT 3 O/L and 1 E/L relays.
11 KV lines Transmission Line	Non-directional IDMT 2 O/L and 1 E/L relays.

 

Selection Chart for 3Ph Induction Motor
Motor Rating,415V,3Ph		Full Load Current (A)	CONTACTOR (A)		OVER LOAD RELAY (A)		BACK UP FUSE (A)	Cable Size
								DOL Starter		STAR-DELTA Starter
HP	KW		DOL	STAR-DELTA	DOL	STAR-DELTA		Alu.	Cu.	Alu.	Cu.
0.75	0.52	1.6	16		1.0 To 1.6		4	1.5	1.5
1	0.75	2	16		1.6 To 2.5		6	1.5	1.5
2	1.5	3.5	16		3.0 To 4.5		10	1.5	1.5
3	2.2	5	16		4.5 To 7.0		10	1.5	1.5
5	3.7	7.5	16		6.5 To 10		16	1.5	1.5
7.5	5.5	11	16	16	10 To 15	4.5 To 7.0	16	2.5	1.5	2.5	1.5
10	7.5	14	16	16	13 To 20	6.5 To 10	20	2.5	2.5	2.5	2.5
12.5	9.3	18	25	16	13 To 20	10 To 15	25	4	2.5	4	2.5
15	11	21	25	16	15 To 22	13 To 20	25	6	4	6	4
20	15	28	32	18	24 To 30	13 To 20	32	10	6	10	6
25	18.5	35	40	25	25 To 30	15 To 22	50	16	10	16	10
30	22.5	40	50	25	32 To 50	24 To 30	50	16	16	16	16
35	26	47	70	32	32 To 50	25 To 30	63	25	16	25	16
50	37	66	70	40	57 To 70	32 To 50	80	35	25	35	25
60	45	80	95	50	70 To 105	32 To 50	100	50	35	50	35
75	55	100	125	70	100 To 150	40 To 57	100	70	50	70	50
90	67.5	120	140	70	100 To 150	57 To 70	160	95	70	95	70
100	75	135	140	95	100 To 150	70 To 105	160	95	70	95	70
125	90	165		125		70 To 105	160			150	95
150	110	200		125		100 To 150	200			185	150

 

MCB Selection Chart For Motor Protection
Kw	HP	1Phase 230V DOL Starting		3Phase 400V DOL Starting		3 Phase 400V Star Delta
		Full Load Current	MCB Selection	Full Load Current	MCB Selection	Full Load Current	MCB Selection	MCB Selection
0.18	0.24	2.8	10	0.9	2	—	—	—
0.25	0.34	3.2	10	1.2	2	—	—	—
0.37	0.5	3.5	10	1.2	2	—	—	—
0.55	0.74	4.8	16	1.8	3	—	—	—
0.75	1.01	6.2	20	2	3	—	—	—
1.1	1.47	8.7	25	2.6	6	—	—	—
1.5	2.01	11.8	32	3.5	10	—	—	—
2.2	2.95	17.5	50	4.4	10	—	—	—
3	4.02	20	63	6.3	16	6.3	16	10
3.75	5.03	24	80	8.2	20	8.2	20	10
5.5	7.37	26	80	11.2	25	11.2	32	16
7.5	10.05	47	125	14.4	40	14.4	40	25
10	13.4	—	—	21	50	21	50	32
15	20.11	—	—	27	100	27	63	40
18.5	24.8	—	—	32	125	32	—	50
22	29.49	—	—	38	125	38	—	63
30	40.21	—	—	51	125	51	—	63

 

RELAY CODE (ANSI)
Code	Type of Relay
1	Master Element
2	Time-delay Starting or Closing Relay
3	Checking or Interlocking Relay
4	Master Contactor
5	Stopping Device
6	Starting Circuit Breaker
7	Rate of Change Relay
8	Control Power Disconnecting Device
9	Reversing Device
10	Unit Sequence Switch
11	Multifunction Device
12	Over speed protection
13	Synchronous-Speed Device
14	Under speed Device
15	Speed or Frequency Matching Device
16	Data Communications Device
17	Shunting or Discharge Switch
18	Accelerating or Decelerating Device
19	Starting-to-Running Transition Contactor
20	Electrically-Operated Valve
21	Distance protection Relay
21G	Ground Distance
21P	Phase Distance
22	Equalizer circuit breaker
23	Temperature control device
24	Volts per hertz relay
25	Synchronizing or synchronism-check device
26	Apparatus thermal device
27	Under voltage relay
27P	Phase Under voltage
27S	DC under voltage relay
27TN	Third Harmonic Neutral Under voltage
27TN/59N	100% Stator Earth Fault
27X	Auxiliary Under voltage
27 AUX	Under voltage Auxiliary Input
27/27X	Bus/Line Under voltage
27/50	Accidental Generator Energization
28	Flame Detector
29	Isolating Contactor
30	Annunciator Relay
31	Separate Excitation Device
32	Directional Power Relay
32L	Low Forward Power
32N	Watt metric Zero-Sequence Directional
32P	Directional Power
32R	Reverse Power
33	Position Switch
34	Master Sequence Device
35	Brush-Operating or Slip-ring Short Circuiting Device
36	Polarity or Polarizing Voltage Device
37	Undercurrent or Under power Relay
37P	Under power
38	Bearing Protective Device / Bearing Rtd
39	Mechanical Condition Monitor
40	Field Relay / Loss of Excitation
41	Field Circuit Breaker
42	Running Circuit Breaker
43	Manual Transfer or Selector Device
44	Unit Sequence Starting Relay
45	Atmospheric Condition Monitor
46	Reverse-Phase or Phase Balance Current Relay or Stator Current Unbalance
47	Phase-Sequence or Phase Balance Voltage Relay
48	Incomplete Sequence Relay / Blocked Rotor
49	Machine or Transformer Thermal Relay / Thermal Overload
49RTD	RTD Biased Thermal Overload
50	Instantaneous Overcurrent Relay
50BF	Breaker Failure
50DD	Current Disturbance Detector
50EF	End Fault Protection
50G	Ground Instantaneous Overcurrent
50IG	Isolated Ground Instantaneous Overcurrent
50LR	Acceleration Time
50N	Neutral Instantaneous Overcurrent
50NBF	Neutral Instantaneous Breaker Failure
50P	Phase Instantaneous Overcurrent
50SG	Sensitive Ground Instantaneous Overcurrent
50SP	Split Phase Instantaneous Current
50Q	Negative Sequence Instantaneous Overcurrent
50/27	Accidental Energization
50/51	Instantaneous / Time-delay Overcurrent relay
50Ns/51Ns	Sensitive earth-fault protection
50/74	Ct Trouble
50/87	Instantaneous Differential
51	Phase Inverse Time Overcurrent IDMT (Time delay phase overcurrent )
51G	Ground Inverse Time Overcurrent
51LR	AC inverse time overcurrent (locked rotor) protection relay
51N	Neutral Inverse Time Overcurrent
51P	Phase Time Overcurrent
51R	Locked / Stalled Rotor
51V	Voltage Restrained Time Overcurrent
51Q	Negative Sequence Time Overcurrent
52	AC circuit breaker
52a	AC circuit breaker position (contact open when circuit breaker open)
52b	AC circuit breaker position (contact closed when circuit breaker open)
53	Exciter or Dc Generator Relay
54	Turning Gear Engaging Device
55	Power Factor Relay
56	Field Application Relay
57	Short-Circuiting or Grounding Device
58	Rectification Failure Relay
59	Overvoltage Relay
59B	Bank Phase Overvoltage
59P	Phase Overvoltage
59N	Neutral Overvoltage
59NU	Neutral Voltage Unbalance
59P	Phase Overvoltage
59X	Auxiliary Overvoltage
59Q	Negative Sequence Overvoltage
60	Voltage or current balance relay
60	Voltage or Current Balance Relay
60N	Neutral Current Unbalance
60P	Phase Current Unbalance
61	Density Switch or Sensor
62	Time-Delay Stopping or Opening Relay
63	Pressure Switch Detector
64	Ground Protective Relay
64F	Field Ground Protection
64R	Rotor earth fault
64REF	Restricted earth fault differential
64S	Stator earth fault
64S	Sub-harmonic Stator Ground Protection
64TN	100% Stator Ground
65	Governor
66	Notching or Jogging Device/Maximum Starting Rate/Starts Per Hour/Time Between Starts
67	AC Directional Overcurrent Relay
67G	Ground Directional Overcurrent
67N	Neutral Directional Overcurrent
67Ns	Earth fault directional
67P	Phase Directional Overcurrent
67SG	Sensitive Ground Directional Overcurrent
67Q	Negative Sequence Directional Overcurrent
68	Blocking Relay / Power Swing Blocking
69	Permissive Control Device
70	Rheostat
71	Liquid Switch
72	DC Circuit Breaker
73	Load-Resistor Contactor
74	Alarm Relay
75	Position Changing Mechanism
76	DC Overcurrent Relay
77	Telemetering Device
78	Phase Angle Measuring or Out-of-Step Protective Relay
78V	Loss of Mains
79	AC Reclosing Relay / Auto Reclose
80	Liquid or Gas Flow Relay
81	Frequency Relay
81O	Over Frequency
81R	Rate-of-Change Frequency
81U	Under Frequency
82	DC Reclosing Relay
83	Automatic Selective Control or Transfer Relay
84	Operating Mechanism
85	Pilot Communications, Carrier or Pilot-Wire Relay
86	Lock-Out Relay, Master Trip Relay
87	Differential Protective Relay
87B	Bus Differential
87G	Generator Differential
87GT	Generator/Transformer Differential
87L	Segregated Line Current Differential
87LG	Ground Line Current Differential
87M	Motor Differential
87O	Overall Differential
87PC	Phase Comparison
87RGF	Restricted Ground Fault
87S	Stator Differential
87S	Percent Differential
87T	Transformer Differential
87V	Voltage Differential
88	Auxiliary Motor or Motor Generator
89	Line Switch
90	Regulating Device
91	Voltage Directional Relay
92	Voltage And Power Directional Relay
93	Field-Changing Contactor
94	Tripping or Trip-Free Relay
Abbreviation Code
AFD	Arc Flash Detector
CLK	Clock or Timing Source
CLP	Cold Load Pickup
DDR	Dynamic Disturbance Recorder
DFR	Digital Fault Recorder
DME	Disturbance Monitor Equipment
ENV	Environmental data
HIZ	High Impedance Fault Detector
HMI	Human Machine Interface
HST	Historian
LGC	Scheme Logic
MET	Substation Metering
PDC	Phasor Data Concentrator
PMU	Phasor Measurement Unit
PQM	Power Quality Monitor
RIO	Remote Input/output Device
RTD	Resistance Temperature Detector
RTU	Remote Terminal Unit/Data Concentrator
SER	Sequence of Events Recorder
TCM	Trip Circuit Monitor
LRSS	Local/Remote selector switch
VTFF	Vt Fuse Fail
Suffixes Description
_1	Positive-Sequence
_2	Negative-Sequence
A	Alarm, Auxiliary Power
AC	Alternating Current
AN	Anode
B	Bus, Battery, or Blower
BF	Breaker Failure
BK	Brake
BL	Block (Valve)
BP	Bypass
BT	Bus Tie
BU	Backup
C	Capacitor, Condenser, Compensator, Carrier Current, Case or Compressor
CA	Cathode
CH	Check (Valve)
D	Discharge (Valve)
DC	Direct Current
DCB	Directional Comparison Blocking
DCUB	Directional Comparison Unblocking
DD	Disturbance Detector
DUTT	Direct Under reaching Transfer Trip
E	Exciter
F	Feeder, Field, Filament, Filter, or Fan
G	Ground or Generator
GC	Ground Check
H	Heater or Housing
L	Line or Logic
M	Motor or Metering
MOC	Mechanism Operated Contact
N	Neutral or Network
O	Over
P	Phase or Pump
PC	Phase Comparison
POTT	Pott: Permissive Overreaching Transfer Trip
PUTT	Putt: Permissive Under reaching Transfer Trip
R	Reactor, Rectifier, or Room
S	Synchronizing, Secondary, Strainer, Sump, or Suction (Valve)
SOTF	Switch On To Fault
T	Transformer or Thyratron
TD	Time Delay
TDC	Time-Delay Closing Contact
TDDO	Time Delayed Relay Coil Drop-Out
TDO	Time-Delay Opening Contact
TDPU	Time Delayed Relay Coil Pickup
THD	Total Harmonic Distortion
TH	Transformer (High-Voltage Side)
TL	Transformer (Low-Voltage Side)
TM	Telemeter
TT	Transformer (Tertiary-Voltage Side)
U	Under or Unit
X	Auxiliary
Z	Impedance

 

Harmonic Effects
Harmonic	R Phase	Y Phase	B Phase	Phase Rotation Sequence	Harmonic Effect
	Rotation	Rotation	Rotation
Fundamental	0°	120°	240°	R-Y-B
3th	3×0°=0°	3×120°=360°=0°	3×240°=720°=0°	No Rotation          (In Phase)	Adds Voltages or Currents in Neutral Wire causing Heating
9th	9×0°=0°	9×120°=1080°=0°	9×240°=2160°=0°
15th	15×0°=0°	15×120°=1800°=0°	15×240°=3600°=0°
21th	21×0°=0°	21×120°=2520°=0°	21×240°=5040°=0°
5th	5×0°=0°	5×120°=600°=(600-720)=(-120°)	5×240°=1200°=(1200-2400)=(-240°)	Rotate Against Fundamental (-) (B-Y-R)	Motor Torque Problems
11th	11×0°=0°	11×120°=1320°=(1320-1400)=(-120°)	11×240°=2640°=(2880-2640)=(-240°)
17th	17×0°=0°	17×120°=2040°=(2040-2160)=(-120°)	17×240°=4080°=(4320-4080)=(-240°)
23th	23×0°=0°	23×120°=2760°=(2760-2880)=(-120°)	23×240°=5520°=(5760-5520)=(-240°)
7th	7×0°=0°	7×120°=840°=(840-720)=(+120°)	7×240°=1680°=(1680-1440)=(+240°)	Rotate with Fundamental (+) (R-Y-B)	Excessive Heating Effect
13th	13×0°=0°	13×120°=1560°=(1560-1440)=(+120°)	13×240°=3120°=(3120-2880)=(+240°)
19th	19×0°=0°	19×120°=2280°=(2280-2160)=(+120°)	19×240°=4560°=(4560-4320)=(+240°)
25th	25×0°=0°	25×120°=3000°=(3000-2880)=(+120°)	25×240°=6000°=(6000-5760)=(+240°)