EE4503 Electrical Systems Design Grounding

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

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

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

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

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

Grounding Components http://cr4.globalspec.com/thread/40145/Grounded-Neutral

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

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

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

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

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

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

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

Grounding AC System Grounding – Exothermic Welding http://www.youtube.com/watch?v=CqixbTQG13M

Grounding AC System Grounding – Cable Size http://www.kroo-suchat.com/File_data/ground.pdf

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) http://irrigation.rid.go.th/rid17/Myweb/machanical/type%20lamp.html

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”

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

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

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)

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

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

Grounding Equipment Grounding – Effective Grounding http://www.iaei.org/magazine/2006/09/new-form-of-mc-cable-crosses-application-boundaries/

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. http://www.cable.alcan.com/NR/rdonlyres/19FC4111-742D-47B7-9A28-06DF8AB4023D/0/EquipmentGroundingConductor.pdf

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

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

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

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

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

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

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)

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

Type of Earthing System IT http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf

Type of Earthing System TT http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf

Type of Earthing System TN-C http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf

Type of Earthing System TN-S http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf

Type of Earthing System TN-C-S http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf

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

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