2. 2
1. SOURCE GROUNDED – EQUIPMENT UNGROUNDED
EARTHING IN LV & MV SYSTEMS
2. SOURCE GROUNDED – EQUIPMENT GROUNDED
3. SOURCES GROUNDED – EQUIPMENT GROUNDED
– WITH BONDING
4. LOW VOLTAGE (415V)
5. MV ( RESISTANCE GROUNDED SYSTEM )
6. MV ( UNGROUNDED SYSTEM )
7. ‘CLEAN’ EARTH
8. UPS SYSTEM EARTHING
3. 3
REFERENCES
• IEEE Std – 80 : GUIDE FOR SAFETY IN AC
SUBSTATION GROUNDING
• IEEE Std – 1100 : GUIDE FOR POWERING AND GROUNDING
ELECTONIC EQUIPMENT
• IS – 3043 : CODE OF PRACTICE FOR EARTHING
• EARTHING PRINCIPLES AND PRACTICES : R W RYDER
• ELECTRICAL EARTHING AND ACCIDENT PREVENTION
: EDITED BY M G SAY
4. 4
EARTHING IN LV & MV SYSTEMS
1. SOURCE GROUNDED – EQUIPMENT UNGROUNDED
• AB – SOURCE OF SUPPLY; C – EQUIPMENT
• B IS EARTHED TROUGH EARTH ELECTRODE 'E'
• FOR EASY CONCEPTUALIZATION, 1 NETWORK
SHOWN
A
V
B
E1
C
H
5. 5
• UNDER NORMAL CONDITIONS, R VERY HIGH.
EVEN IF A PERSON TOUCHES THE BODY, NO CURRENT
FLOWS THROUGH HIM
• INSULATION FAILURE OF EQUIPMENT R = 0
• CURRENT THROUGH PERSON
V 240
H = ------------ = ------------ 120 mA
RH + RE1 2000 + 1
• THIS CURRENT IS SMALL AND
NOT SUFFICIENT TO
BLOW THE FUSE
• BUT EVEN THIS SMALL
CURRENT CAN BE
DANGEROUS TO A PERSON ( IEEE STD - 116 mA FOR 1 Sec )
A
RC
R
X
RH
C
B
RE1
V
6. 6
2. SOURCE GROUNDED – EQUIPMENT GROUNDED
• B & C ARE EARTHED
THROUGH EARTH
ELECTRODES 'E1' & 'E2'
• INSULATION FAILURE
OF EQUIPMENT R = 0
• REQ = RE2 RH
= 1 2000 = 1
C
F
RC
R
X
RE1
RE2 RH
A
B
V
7. 7
• FAULT CURRENT
• F IS SIGNIFICANT BUT NOT VERY HIGH.
FUSE MAY OR MAY NOT BLOW
• H - CURRENT THROUGH PERSON LOW BUT
NOT INSIGNIFICANT
V
F = ------------
REQ + RE1
240
= ------------ 120 A
1 + 1 < 120 mA >
1
H = ----------- x 120 60 mA
1 + 2000 < 120 mA >
C
F
RC
R
X
RE1
RE2 RH
A
B
V
8. 8
• BONDING CONDUCTOR – SHOWN IN RED
• PHYSICAL CONNECTION BETWEEN EQUIPMENT CASING
AND SOURCE
• ALSO CALLED EARTH CONTINUITY CONDUCTOR
• BONDING CONDUCTOR RESISTANCE : RB VERY SMALL
3. SOURCE GROUNDED – EQUIPMENT GROUNDED –
WITH BONDING
• FIG_EA_20
9. 9
240
F = --------- = 24 kA
0.01
• F IS VERY HIGH. FUSE WILL BLOW INSTANTANEOUSLY.
• HUMAN SAFETY INHERENTLY ACHIEVED
• CONCLUSION
DO NOT DEPEND ON 'MOTHER EARTH' FOR
RETURN OF FAULT CURRENT. DEPEND ON PHYSICAL
EARTH CONTINUITY CONDUCTOR (BONDING) THAT
RUNS FROM EQUIPMENT TO SOURCE.
• EVEN ASSUMING RB = 0.01 , FAULT CURRENT
• FIG_EA_20
IF FAULT CURRENT IS NOT DISCHARGED TO EARTH,
STEP & TOUCH POTENTIALS ARE IRRELEVANT.
10. 10
1- F SUPPLY TO EQUIPMENT
A
A
RC
R
V
X
RE1 RB RE2 RH
E2
EQUIPMENT
GROUNDED
WITH BONDING
E1
B H B
C
C V
FIG_EA_20
SOURCE
GROUNDED
11. 11
1- F SUPPLY TO EQUIPMENT
A
A
RC
R
V
X
RE1 RB RE2 RH
E2
EQUIPMENT
GROUNDED
WITH BONDING
E1
B H B
C
C V
FIG_EA_20
SOURCE
GROUNDED
12. 12
4. LOW VOLTAGE (415V)
• GENERALLY SOLIDLY GROUNDED
• IE RULES
• IF FOR ANY REASON, IF LV SYSTEM IS NOT SOLIDLY
GROUNDED, SPECIAL PERMISSION FROM ELECTRICAL
INSPECTOR REQUIRED
• MYTH : EARTH IS GOOD EQUIPMENT GROUNDING
CONDUCTOR
• REALITY : EARTH IS THE MOST UNRELIABLE
EQUIPMENT GROUNDING CONDUCTOR
13. 13
• BEST EARTH ELECTRODE RESISTANCE 1
• ON 415 V SYSTEM, IF ONLY EARTH IS USED FOR RETURN OF
FAULT CURRENT,
MAX (415/3) / 1
MAX 240 AMPS
• IF FAULT CURRENT IS LIMITED TO 240 A, NEITHER O/C RELAY
NOR FUSE WILL EVER OPERATE !
• FIG_EA_1
EARTH : UNRELIABLE EARTHING CONDUCTOR
15. 15
• EARTH SHALL NOT BE TREATED AS SOLE EQUIPMENT
GROUNDING CONDUCTOR FOR FAULT CURRENT
RETURN PATH
• MAKE AS MANY SUPPLEMENTARY CONNECTION TO
EARTH FROM EQUIPMENT AS YOU WISH
• BUT MAKE SURE THAT ALL EQUIPMENT ARE
CONNECTED TO GROUNDING GRID (EARTH
CONTINUITY) CONDUCTOR WHICH SHALL BE
CONNECTED TO SOURCE NEUTRAL
• CONCLUSIONS
16. 16
• MAJORITY OF FAULT CURRENTS SHALL BE CARRIED BY
GROUNDING GRID CONDUCTOR AND VERY LITTLE BY
'MOTHER' EARTH
• IF EARTH CURRENT IS LESS, TOUCH POTENTIAL IS ALSO
LESS
• FIG_EA_26
• IF NOT DONE LEADS TO GROUND FAULT RELAYING
PROBLEMS
• EARTH CONDUCTOR MUST RUN ALL OVER THE PLANT
AND MUST CARRY RETURN CURRENT BACK TO SOURCE
NEUTRAL
LOW VOLTAGE (415V)
• CORRECT METHOD FIG_EA_99A
• WRONG METHOD FIG_EA_99B
18. 18
EARTHING IN LV SYSTEM
CORRECT METHOD
M
E
MCC
E
PCC
R Y B N
6.6KV
E
40 x 6
FIG_EAR_99A
415V
19. 19
EARTHING IN LV SYSTEM
WRONG METHOD
M
E
MCC
E
PCC
R Y B N
6.6KV
E
40 x 6
FIG_EAR_99B
E
415V
20. 20
• UNSAFE EARTHING
• NO EARTH CONTINUITY
CONDUCTOR
• SAFE EARTHING
• WITH EARTH
CONTINUITY CONDUCTOR
21. 21
• EVEN HERE THE EARTH CONDUCTOR MUST RUN ALL
OVER THE PLANT AND MUST CARRY RETURN CURRENT
BACK TO NGR
5. MV ( RESISTANCE GROUNDED SYSTEM )
• FIG_EA_27
ANIMATION
• DO NOT EARTH NGR BODY !
28. 28
7. ‘CLEAN’ EARTH
❖ ELECTRONIC EQUIPMENT EARTHING
• FIG_EA_51 - CORRECT METHOD
• FIG_EA_52 - WRONG METHOD
• FIG_EA_53 - MONITORING
• NEUTRAL CURRENT HIGH
• CURRENT THROUGH ISOLATED GROUND
HIGH
29. 29
‘CLEAN’ EARTH
• TWO CARDINAL PRINCIPLES
• NEUTRAL CONDUCTOR AND GROUND CONDUCTOR
CONNECTED ONLY AT THE SERVICE ENTRANCE. FROM
THIS POINT ON, NEUTRAL AND GROUND CONDUCTORS
SHOULD NOT BE BONDED TOGETHER. i.e. NEUTRAL AND
GROUND CONDUCTORS SHOULD NEVER TOUCH EACH
OTHER AFTER LEAVING SERVICE ENTRANCE PANEL
BOARD.
• UNBALANCED LOAD CURRENTS SHALL RETURN
ONLY THROUGH THE NEUTRAL BACK TO THE SERVICE
ENTRANCE. GROUND SHALL CARRY ONLY FAULT
CURRENT AND NOT UNBALANCED LOAD CURRENTS.
30. 30
• MYTH
ELECTRONIC EQUIPMENT REQUIRE A ‘CLEAN,
DEDICATED AND ISOLATED GROUND’ AND SHOULD BE
ISOLATED FROM DIRTY ‘POWER EARTH’. THIS IS A
FAIRY TALE AND NOT AS PER CODES.
‘CLEAN’ EARTH
31. 31
N N
ELECTRONIC EQUIPMENT EARTHING : CORRECT METHOD
SOURCE PANEL RECEPTACLE LOAD
N
N
N
IG
IG
G
G
G
FIG_EA_51
32. 32
ELECTRONIC EQUIPMENT EARTHING : WRONG METHOD
CLEAN EARTH?
N N
SOURCE PANEL RECEPTACLE LOAD
N
N
N
IG
IG
G
G
G
FIG_EA_52
POWER EARTH
