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Assumption University Thailand EE4503 Electrical Systems Design Grounding 1.

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Presentation on theme: "Assumption University Thailand EE4503 Electrical Systems Design Grounding 1."— Presentation transcript:

1 Assumption University Thailand EE4503 Electrical Systems Design Grounding 1

2 Assumption University Thailand Topics Introduction to Grounding Grounding of Electrical Systems Grounding Systems Grounding Resistant 2

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

4 Assumption University Thailand Grounding Category 4 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

5 Assumption University Thailand Grounding Components 5 Grounding Electrode (System) Grounding Electrode Conductor Grounded Conductor Main Bonding Jumper Equipment Grounding Conductor

6 Assumption University Thailand Grounding Components 6 Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์

7 Assumption University Thailand Grounding Components 7

8 Assumption University Thailand Grounding Common Grounding Systems 8 System Grounding Service Equipment Grounding Separately Derived System Equipment Grounding Computer Grounding

9 Assumption University Thailand Grounding AC System Grounding 9 “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 Assumption University Thailand Grounding AC System Grounding – 50V 10 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 Assumption University Thailand Grounding AC System Grounding – 50 to 1kV 11 Usually at the distributed transformer Neutral is grounded

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

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

14 Assumption University Thailand Grounding AC System Grounding – Electrode 14 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 Assumption University Thailand Grounding AC System Grounding – Exothermic Welding 15

16 Assumption University Thailand Grounding AC System Grounding – Cable Size 16

17 Assumption University Thailand Grounding AC System Grounding – Cable Size 17 Meter (A)  MCB (A) Cable Sizing (sq.mm.) Voltage (V) Incoming Cable in Air (Grounding) Incoming Cable in Conduit (Grounding) 5 (15)1164 (10)4,10**(10) (45)15010 (10)16 (10) (100) (10)50 (16) (150) (10)70 (25) (45)35010 (10)16 (10) (100) (10)50 (16) (150) (10)70 (25) (25)150 (35) (50)500 (70)750

18 Assumption University Thailand Grounding Service Equipment Grounding 18 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 Assumption University Thailand Grounding Separately Derived System 19 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 Assumption University Thailand Grounding Equipment Grounding 20 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 Assumption University Thailand Grounding Equipment Grounding – What to be grounded? 21 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 Assumption University Thailand 22 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 Grounding Equipment Grounding – What to be grounded?

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

24 Assumption University Thailand 24 Grounding Equipment Grounding – Effective Grounding

25 Assumption University Thailand Grounding Equipment Grounding – Sizing 25 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 Assumption University Thailand Grounding Equipment Grounding – Sizing 26 Rated Circuit Breaker or Overload Protector (A) Ground Cable Size (mm 2 ) (recommended 2.5) Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์

27 Assumption University Thailand Grounding Computer Grounding 27 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 Assumption University Thailand Grounding Electrode System Earth 28 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 Assumption University Thailand 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 29

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

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

32 Assumption University Thailand Earthing Scheme 32 2 nd : 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 Assumption University Thailand Earthing Scheme 33 3 rd (if any): arrangement of neutral (N) and protective conductor (PE) –S means separation between N & PE –C means common between N & PE

34 Assumption University Thailand Type of Earthing System IT 34

35 Assumption University Thailand Type of Earthing System TT 35

36 Assumption University Thailand Type of Earthing System TN-C 36

37 Assumption University Thailand Type of Earthing System TN-S 37

38 Assumption University Thailand Type of Earthing System TN-C-S 38

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

40 Assumption University Thailand Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์ Reference 40


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