1. Grounding & Shielding Ved Prakash Sandlas Director General
Amity Institute of Space Science & Technology, Noida
Principal Adviser, Cogent EMR Solutions Ltd, New Delhi ( )
Distinguished Scientist and Chief Controller R & D, DRDO ( )
Director, Defence Electronics Applications Lab (DEAL), Dehradun ( )
Group Director, Electronics, VSSC, Thiruvanathapuram ( )
Project/Mission Director, SLV-3, ISRO ( )
AISST, Noida, Feb 8, 2010

2. REASONS FOR GROUNDING
Lightning Protection to Buildings, Structures and Equipment
Shock and Safety hazard control in Equipment, Laboratories, Hospitals and Homes
Faraday Shielding of Cables
Common Ground Reference for Measurements
Common Mode EMI Filters
Electrostatic Hazard Control
Ground (Return) Line, Signal Return and Power Return
Analog Ground, Digital Ground and Power Ground

3. TRANSMISSION SYSTEM USING GROUND AS CURRENT RETURN PATH
TRANSMISSION LINE
LOAD CURRENT
GROUND RODS
SOURCE
LOAD
RETURN CURRENT
GROUND (EARTH)
TRANSMISSION SYSTEM USING GROUND AS CURRENT RETURN PATH

4. SINGLE POINT OR STAR GROUNDING1 2 3
SYSTEM GROUND 4 5 6
EARTH GROUND

5. MULTI POINT GROUNDING 1 2 3 GROUNDING BRAID CONDUCTING GROUND PLANE
GROUNDING LUGS
TO EARTH GROUND

6. HYBRID GROUNDING RS RL VS C LOW FREQUENCY------------SINGLE POINT
SOURCE CHASSIS
LOAD CHASSIS
COAXIAL CABLE RS
OUTER BRAID GROUNDED RL VS C
LOW FREQUENCY GROUND
HIGH FREQUENCY GROUND
HYBRID GROUNDING
LOW FREQUENCY SINGLE POINT
HIGH FREQUENCY MULTI POINT

7. SAFETY GROUND AND EMI ISOLATION
POWER DISTRIBUTION PANEL
COMPUTER (CPU)
PERIPHERAL
EARTH WIRE
SAFETY GROUND AND EMI ISOLATION

8. _ _ CASSIS RETURN _ GROUND (EARTH) RETURN+
POWER SUPPLY
LOAD _
COMMON (FLOATING) RETURN +
POWER SUPPLY
LOAD _
CASSIS RETURN +
POWER SUPPLY
LOAD _
GROUND (EARTH) RETURN

9. SHIELDING MECHANISM FOR PLANE WAVE
Incident Wave EY HZ EY EY HZ HZ EY EY HZ HZ
Attenuated Wave
Barrier of Finite Thickness
SHIELDING MECHANISM FOR PLANE WAVE

10. Absorption Loss, A = 3.34 t √fGµ dB
Where,
t = Shield thickness in mils
f = Frequency in MHz
G = Conductivity relative to Copper
(Copper = 1, Aluminum = 0.61, Brass = 0.26, Iron = 0.17,
Stainless Steel = 0.02)
µ = Permeability relative to Vacuum
(Copper = 1, Aluminum = 1, Brass = 1, Stainless Steel = 1
Iron = 1000, Mu Metal = 80,000, Perm Alloy = 80,000)
1 mil of Copper at 1 GHz shall give over 100 dB absorption loss
1/8 inch (~ 0.3 cm) Iron sheet at 50 Hz gives 50 dB absorption loss

11. Shielding Absorption LossdB
300
100 30 10 3 1
IRON
1/8 inch
1/8 inch
10 mils
10 mils
1 mil
1 mil
COPPER
k 10k 100k 1M 10M 100M 1G
Frequency Hz

13. For Plane Wave, Reflection Loss:
R = log dB
Reflection loss for plane wave at low frequencies is the major shielding mechanism
Also, high G and low µ is more effective (low surface impedance compared to 377 ohms)
Also, at high frequencies, the skin depth decreases or surface resistivity increases (surface impedance increases), reducing reflection loss
At VHF and UHF, absorption loss is more important G µf

14. Reflection Loss for Plane WavedB
250
200
150
100 50
COPPER
IRON
k 10k 100k 1M 10M 100M 1G
Frequency Hz

15. For high impedance wave in near field (Electric Field)
R = log dB
Where,
r = Distance from source to barrier in inches (<<  / 2)
F = Frequency in Hz
For low impedance wave in near field (Magnetic Field)
R = 20 log √µ / FG r √FG / µ dB
An interesting condition is achieved for magnetic field reflection loss for iron with 1 inch separation, where it approaches 0 dB at 30 kHz indicating matching of wave impedance and surface impedance G
F3µr2
0.462 r

16. Reflection Loss for Electric FieldsdB
250
200
150
100 50
COPPER
r = 30m 1m
1inch
30m 1m
r = 1 inch
Plane Wave
IRON
k 10k 100k 1M 10M 100M 1G
Frequency Hz

17. Reflection Loss for Magnetic FieldsdB
125
100 75 50 25
Plane Wave
COPPER
30m 1m
r = 1 inch
r = 30m 1m
1inch
IRON
k 10k 100k 1M 10M 100M 1G
Frequency Hz

18. ELECTRIC FIELD COUPLING
Also called capacitive coupling increases with increase in circuit impedance and is the primary contributor at high frequencies
To reduce electric field coupling
Isolate the culprit circuit
Shortest possible, point to point wiring
Faraday shielding

19. SINGLE CONDUCTOR SHIELDED
CS1 CC
SHIELD CC
CS1
SHIELD NODE
LOW IMPEDANCE BOND ZL VS
SINGLE CONDUCTOR SHIELDED

20. BOTH CONDUCTORS SHIELDED
CS1 CC
CS2
SHIELDS
SHIELD NODES
CS1 CC
CS2 ZL VS
LOW IMPEDANCE BONDS
BOTH CONDUCTORS SHIELDED

21. TRANSFORMER SHIELDING AND GROUNDINGC A C RL P S B D B D
CASE
NOISE
COMMON MODE NOISE COUPLING A C A C RL P S
NOISE B D B D
DIFFERENTIAL MODE NOISE COUPLING
TRANSFORMER SHIELDING AND GROUNDING

22. TRANSFORMER SHIELDING AND GROUNDINGC C
CASE
NODE RL P S B D B D
NOISE
SHIELD
COMMON MODE NOISE SHIELDING
NODE A C A C RL P S
NOISE B D B D
DIFFERENTIAL MODE NOISE SHIELDING
TRANSFORMER SHIELDING AND GROUNDING

23. BOTH COMMON & DIFFERENTIAL MODE NOISE SHIELDING
TWO SHIELDS A C P S B D
NODES A C Ic Id RL
NOISE (d) Id Ic Ic Id B D Ic Ic Ic Ic
NOISE (c)
BOTH COMMON & DIFFERENTIAL MODE NOISE SHIELDING

24. MAGNETIC FIELD COUPLING
Predominates for low frequencies and low impedance circuits. Also generates cross-talk and hum in audio and telecommunication circuits.
To reduce magnetic field coupling
Increase impedance in culprit circuit
Avoid ground loop currents and reduce loop area
Use dedicated return lines and twisted pairs
Shields of permeability greater than one
Sensitive circuits should be used in differential mode
Use of isolation transformers and optical couplers

25. Large Loop Area and no Separate Ground ReturnZs
Loop Area = l x h Vs ZL h l
Large Loop Area and no Separate Ground Return

26. Reduce Loop Area by Reducing Height Above Ground PlaneZs Vs ZL l h
Reduce Loop Area by Reducing Height Above Ground Plane

27. Dedicated Return – No Ground or Ground One End OnlyZs h Vs ZL l
Dedicated Return – No Ground or Ground One End Only

28. Twisted Wire Return – No Ground or Ground One End OnlyZs Vs ZL
Twisted Wire Return – No Ground or Ground One End Only

29. Breaking of Ground Loop With Isolation TransformerZs Vs ZL
Source and/or Load Grounded to Body
Breaking of Ground Loop With Isolation Transformer

30. SHIELDED CABLES AND GROUNDING
GROUND CURRENT LOOPS IN COAX
FARADAY SHIELDING OF COAX BY TRIAX
SHIELDED TWISTED PAIR – TWINAX
SINGLE POINT GROUNDING OF TWINAX
QUADRAX WITH EXTRA SHIELD
SHIELDED CABLES AND GROUNDING

31. All measurements are at 100 kHz and the wires are 1 inch above the ground plane
A large coupling loop area consisting of the outgoing wire length and ground plane return path
Coupling is primarily magnetic
The wire shield is grounded at one end and offers essentially no magnetic field shielding
This is taken as the reference case at 0 dB
(a) 0 dB – Reference Case

32. (a) 0 dB – Reference Case (b) – 2 dB
Twisted – 6 T/ft
(a) 0 dB – Reference Case
(b) – 2 dB
Uses twisted wire pair for magnetic field decoupling
But defeated because both load and source return wire ends are also grounded to the ground plane
Performance almost same as (a)
2 dB improvement only a measurement error

33. (a) 0 dB – Reference Case (b) – 2 dB
Twisted – 6 T/ft
(a) 0 dB – Reference Case
(b) – 2 dB
Similar to (a)
Except the shield return path, which would have resulted in significant magnetic field decoupling, was also defeated by grounding at both ends to result in large ground loop area
(c) – 5 dB

34. (a) 0 dB – Reference Case (b) – 2 dB
Twisted – 6 T/ft
(a) 0 dB – Reference Case
(b) – 2 dB
Shows significant improvement because of twisted wire pair
Confirming that the main coupling mode was indeed magnetic
Ground loop removed by floating the load end
(c) – 5 dB
(d) – 49 dB

35. (a) 0 dB – Reference Case (b) – 2 dB
(d) – 49 dB
Twisted – 6 T/ft
(b) – 2 dB
(e) – 57 dB
Coaxial line seems to offers better magnetic shielding, may be because of smaller loop area than twisted pair
Also outer sheath acting as return makes effective separation as almost zero
It is also possible that some electric field component also got removed
If twisting is not good or only few twists per unit length then it may offer less magnetic shielding than a good coaxial line
(c) – 5 dB

36. (a) 0 dB – Reference Case (b) – 2 dB
(d) – 49 dB
Twisted – 6 T/ft
(b) – 2 dB
(e) – 57 dB
Further improvement by improved electric field coupling
(c) – 5 dB
(f) – 64 dB

37. (a) 0 dB – Reference Case (d) – 49 dB (g) – 64 dB Twisted – 6 T/ft
(b) – 2 dB
(e) – 57 dB
Same performance as (f)
Indicates that length of wires are small fraction of wave length
De coupling performance of shield grounding at one end is same as for both ends
(c) – 5 dB
(f) – 64 dB

38. (a) 0 dB – Reference Case (d) – 49 dB (g) – 64 dB Twisted – 6 T/ft
(b) – 2 dB
(e) – 57 dB
(h) – 71 dB
It is not clear why better performance than (g)
Reduction of loop area seems to the reason
(c) – 5 dB
(f) – 64 dB

39. (a) 0 dB – Reference Case (d) – 49 dB (g) – 64 dB Twisted – 6 T/ft
(b) – 2 dB
(e) – 57 dB
(h) – 71 dB
Increased twisting increase magnetic field coupling
Improvement shown from (d) to (e) had hinted that twisting was not very effective
Also reduction in differential mode signals
Twisted – 18 T/ft
(c) – 5 dB
(f) – 64 dB
(i) – 79 dB

40. PSLV C 11

41. PSLV C 11

43. THIRD PIN Ground Pin, Green Wire or Earth Connection
75 mA through body considered fatal
Filters or Capacitors connected between equipment circuitry and case should not result in more than 5 mA (for 0.1 µf) through earth line
When there are a large number of users sharing a common earth line in the same building, this safety wire can carry plenty of trash and interference created by ON/OFF transients, leakage currents and radiations pickups – use 2 pins and non-metallic body
Obviously, one should not share the ground line with lightning earth strip or water plumbing

44. Thank You