1. EE4503 Electrical Systems Design
Grounding

2. Topics Introduction to Grounding Grounding of Electrical Systems
Grounding Systems
Grounding Resistant

3. Grounding Grounding or Earthing
Make the potential difference become the same as ground/earth.
For human safety and equipment safety
Follow NEC Article 250

4. Grounding Category
System Grounding: connect the “live” portion of the electrical system to ground, e.g. neutral
Equipment Grounding: connect a part (having no current) of the equipment to ground, e.g. case
live = having current

5. Grounding Components Grounding Electrode (System)
Grounding Electrode Conductor
Grounded Conductor
Main Bonding Jumper
Equipment Grounding Conductor

6. Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์
Grounding Components
Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์

7. Grounding Components

8. Grounding Common Grounding Systems
System Grounding
Service Equipment Grounding
Separately Derived System
Equipment Grounding
Computer Grounding

9. Grounding AC System Grounding
“live” portions of the electrical system
Protect Overvoltage: specially from lightning
Stabilize voltage level referring to ground
Be part of protection circuit: be part of the short- circuit current
50V, 50 to 1kV, more than 1kV

10. Grounding AC System Grounding – 50V
NEC Standard
The source
is stepped down from more than 150V
is stepped down from the ungrounded system
Cable in over the ground outside the building

11. Grounding AC System Grounding – 50 to 1kV
Usually at the distributed transformer
Neutral is grounded

12. Grounding AC System Grounding – Electrode
Grounding Electrode Conductor
Connected to three parts
Grounded Conductor: usually neutral line
Equipment Grounding Conductor
Main Bonding Jumper

13. Grounding AC System Grounding – Electrode
Cable: continuous copper cable with insulator
Installation: connect to a surface, recommend conduit
EMC: metal component needed to be connect to ground

14. Grounding AC System Grounding – Electrode
Cable: continuous copper cable with insulator
Installation: connect to a surface, conduit (recommended)
EMC: metal component needed to be connect to ground
Connection: Exothermic Welding, or other recommended methods

15. Grounding AC System Grounding – Exothermic Welding

16. Grounding AC System Grounding – Cable Size

17. Grounding AC System Grounding – Cable Size
Meter
(A) 
MCB (A)
Cable Sizing (sq.mm.)
Voltage (V)
Incoming Cable in Air (Grounding)
Incoming Cable in Conduit (Grounding)
5 (15) 1 16
4 (10)
4,10**(10)
300
15 (45) 50
10 (10)
16 (10)
30 (100)
100
25 (10)
50 (16)
50 (150)
125
35 (10)
70 (25) 3
750
200
250
95 (25)
150 (35)
400
500
240 (50)
500 (70)

18. Grounding Service Equipment Grounding
Usually two points of grounding: at the transformer and at the main distribution box
“Main Bonding Jumper” connects the metal part of the main distribution box to ground
“Main Bonding Jumper” (now) connects to the grounded conductor
Same calculation as “System Grounding”

19. Grounding Separately Derived System
Electrical systems that are separated inside the facility (after the utility): e.g. from utility and generator
Common Neutral: grounded only at the main distribution box
Isolated Neutral: grounded separately and have the isolated ground rod

20. Grounding Equipment Grounding
Grounding for the “non-live” metal portion
The enclosure has the same potential level as the ground (protected for human contact)
Improve short-circuit protection: conductor touching enclosure
Path for the leakage current

21. Grounding Equipment Grounding – What to be grounded?
Metal enclosure & Protected Fence: metal conduit, panelboard enclosure, electric crane, elevator’s enclosure
Protected fence: HV station
Electrical Appliance specially with outlet: more than 150V, except having proper insulator (e.g. double insulator)

22. Grounding Equipment Grounding – What to be grounded?
Fixed Equipment with hard wires specially able to be touched
Close contact to human: grounded within 2.4m from ground and 1.5m from wall
Electrical contact to metal
Wet area

23. Grounding Equipment Grounding – Effective Grounding
Continuity
Low Impedance
High Ampacity
Copper: with or without insulator
Busware: that specified for grounding
Metal Armor of some cables: AC, MI, MC

24. Grounding Equipment Grounding – Effective Grounding

25. Grounding Equipment Grounding – Sizing
Tables (if common ground cable, take maximum one)
In general: according to rating of CB
For motor: according to the rating of overload protection.

26. Grounding Equipment Grounding – Sizing
Rated Circuit Breaker or Overload Protector
(A)
Ground Cable Size (mm2) 16
1.5 (recommended 2.5) 20
2.5 40 4 70 6
100 10
200
400 25
500 35
Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์

27. Grounding Computer Grounding
Power Distribution Grounding
Single Ground Point to protect “Ground Loop”
High Frequency Grounding
in the order of kHz or MHz
60cm x 60cm conductor grid
Recommend common ground electrode

28. Grounding Electrode System Earth
Refered as 0
Deeper in the ground (more humidity)  lower resistance
Good for make the reference voltage as 0
** not capable enough to conduct high current

29. Grounding Electrode System Electrode
Existing Electrode
Underground metal pipes
Building structures
Pile
Under ground metal structures
Made Electrode
Ground Rods
Concrete Encased Electrode
Buried Plate
Ring
Grid

30. Grounding Electrode System Ground Rod
Copper rod with at least 16mm in diameter and 2.4 m in length
Few longer rods are better than many short rods

31. Earthing Scheme 2,3 or 4 characters
1st: relation between distribution system and earth
T means single point connecting to earth
I means isolated from earth

32. Earthing Scheme 2nd: relation exposed conductive part and earth
T means no connection to the electrical system
N means there is a connection between the exposed conductive and electrical system (neutral)

33. Earthing Scheme
3rd(if any): arrangement of neutral (N) and protective conductor (PE)
S means separation between N & PE
C means common between N & PE

34. Type of Earthing System IT

35. Type of Earthing System TT

36. Type of Earthing System TN-C

37. Type of Earthing System TN-S

38. Type of Earthing System TN-C-S

39. Resistance to Ground By E.I.T. standard 5 Ohm
Some area, authority might allow up to 25 Ohm
If cannot achieve, try adding extra electode

40. Reference Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์
Depend on the area, end-user can connect to the “meter” of the authority in three ways.