Earthing & grounding difference

Presentation for basic difference between Earthing & grounding

1. Presented By : Anurag Singh [phone] S3 Energy Pvt. Ltd. Project Operations

2. What is earthing and why it is done? C onnecting the metallic (conductive) Parts of an Electric appliance or installations to the earth (ground) so as to have discharge of electrical energy . Its Need: To ensure safety from electric shocks .

3. How it Works & Its Importance? Earthing is used to protect us from an electric shock. It does this by providing a path (a protective conductor) for a fault current to  flow  to earth. One of the most  important  reasons for  grounding  electrical currents is that it protects your appliances, your home and everyone in it from surges in electricity. ... If your electrical system is grounded, all of that excess electricity will go into the earth — rather than frying everything connected to your system.

4. How grounding is different from earthing? E arthing  is done not for return path but only for protection of delicate equipments. It is an alternate low resistance path for current. When we take out the neutral for a three phase unbalanced connection and send it to ground, it is called grounding .  Grounding  is done to balance unbalanced load.

5. Earthing… Earthing means connecting the dead part (it means the part which does not carries current under normal condition) to the earth for example electrical equipment’s frames, enclosures, supports etc . The purpose of earthing is to minimize risk of receiving an electric shock if touching metal parts when a fault is present . Under fault conditions the metal parts of an electrical installation such as frames, enclosures, supports, fencing etc. may attain high Current so that any person or stray animal touching these parts can get Electric Shock . To avoid electrical shock metal parts of the electrical system are connected to the general mass of earth by means of an earthing system comprising of earth conductors to conduct the fault currents safely to the ground. Earthing has been accomplished through bonding of a metallic system to earth. It is normally achieved by inserting ground rods or other electrodes deep inside earth . Earthing is to ensure safety or Protection of electrical equipment and Human by discharging the electrical energy to the earth . G reen wire is used for this as a nomenclature.

6. Grounding… Grounding means connecting the live part (it means the part which carries current under normal condition) Grounding is done for the protection of power system equipment and to provide an effective return path from the machine to the power source. For example grounding of neutral point. Because of lightening, line surges or unintentional contact with other high voltage lines , high voltages can develop in the electrical distribution system wires. Grounding provides a safe, alternate path around the electrical system of your house thus minimizing damage from such occurrences . G enerally Black wire is used for this as a nomenclature.

7. Micro Difference between earthing & Grounding: There is no major difference between earthing and Grounding, both means  “Connecting an electrical circuit or device to the Earth”.   - This serves various purposes like to drain away unwanted currents. Even though there is a micro difference between grounding & earthing . Difference in Terminology : In USA term Grounding is used but in UK term Earthing is used. Balancing the Load Vs Safety: Ground is a source for unwanted currents and also as a return path for main current some times. While earthing is done not for return path but only for protection of delicate equipments. It is an alternate low resistance path for current. When we take out the neutral for a three phase unbalanced connection and send it to ground, it is called grounding. Grounding is done to balance unbalanced load. While earthing is used between the equipment and earth pit so as to avoid electrical shock and equipment damage.

8. Equipment Protection Vs Human Safety: Earthing is to protect the circuit elements whenever high voltage is passed by thunders or by any other sources while Grounding is the common point in the circuit to maintain the voltage levels. Earthing is used for the safety of the human body in fault conditions while Grounding (As neutral earth) is used for the protection of equipments.

9. Why are there 3 pins on a plug? This is connected to the earth  pin . This is  used  when the appliance has a metal casing to take any current away, in case if the live wire comes in contact with the casing. A  3 - pin plug  consists of  three pins  (hence the name). ... This type  plug  is commonly  used  for heavy appliances such as the air-conditioners

10. Why the earth pin is longer? The  earth pin  on a plug is   longer  than the live and neutral   pins . This means the earth pin  is the first to connect and the last to disconnect. When inserting the plug, the  earth   connection is made before the current carrying contacts of the plug become live.

11. Purpose of Earthing: Safety for Human life/ Building/Equipments: To save human life from danger of electrical shock i.e. To provide an alternative path for the fault current to flow so that it will not endanger the user. To protect buildings, machinery & appliances. To ensure that all exposed conductive parts do not reach a dangerous potential. To provide safe path to dissipate lightning and short circuit currents. Over voltage protection: Lightning, line surges or unintentional contact with higher voltage lines can cause dangerously high voltages to the electrical distribution system. Earthing provides an alternative path around the electrical system to minimize damages in the System.

12. POINTS TO BE EARTHED Earthing is not done anyhow. According to IE rules and IEE (Institute of Electrical Engineers) regulations, Earth pin of 3-pin lighting plug sockets and 4-pin power plug should be efficiently and permanently earthed. All metal casing or metallic coverings containing or protecting any electric supply line or apparatus such as GI pipes and conduits enclosing VIR or PVC cables, iron clad switches, iron clad distribution fuse boards etc should be earthed (connected to earth). The frame of every generator, stationary motors and metallic parts of all transformers used for controlling energy should be earthed by two separate and yet distinct connections with the earth. In a dc 3-wire system, the middle conductors should be earthed at the generating station. Stay wires that are for overhead lines should be connected to earth by connecting at least one strand to the earth wires.

13. Components of Earthing System A complete electrical earthing system consists on the following basic components. Earth Continuity Conductor Earthing Lead Earth Electrode

14. Earth Continuity Conductor or Earth Wire That part of the earthing system which interconnects the overall metallic parts of electrical installation e.g. conduit, ducts, boxes, metallic shells of the switches, distribution boards , fuses, Regulating and controlling devices, metallic parts of electrical machines such as, motors, generators, transformers and the metallic framework where electrical devices and components are installed is known as earth wire or earth continuity conductor The resistance of the earth continuity conductor is very low.   resistance of earth wire should be less than 1Ω . Size of the Earth Continuity Conductor or Earth Wire depends on the  cable size   used in the  wiring circuit The cross sectional area of the  Earth Continuity Conductor  should not be less than the half of the cross sectional area of the thickest wire used in the  electrical wiring installation . Generally, the size of the bare copper wire used as earth continuity conductor is 6mm . But keep in mind that, don’t use less than 2mm as earth wire.

15. Earthing Lead or Earthing Joint The conductor wire connected between earth wire and earth electrode is called “Earthing lead”. & The point where earth continuity conductor and earth electrode meet is known as “connecting point ”. Earthing lead is the final part of the earthing system which is connected to the earth electrode (which is underground) through earth connecting point. C opper wire can be used as earthing lead , Copper strip is also used for high installation and it can handle the high fault current because of wider area than the copper wire .

16. Size of the Earthing Lead The size or area of earthing lead should not be less than the half of the thickest wire used in the installation. The largest size for earthing lead is 6mm and the minimum size should not be less than 4mm. If the load current is 200A from the supply voltage, then it is recommended to use copper strip instead of double earthing lead. The earth lead connection methods is shown in fig.

17. Earthing Electrode or Earth Plate A metallic electrode or plate which is buried in the earth (underground) and it is the last part of the electrical earthing system is called earth plate or earth electrode. A metallic plate, pipe or rode can be used as an earth electrode which has very low resistance and carry the fault current safely towards ground (earth).

18. Size of Earthing Electrode Both copper and iron can be used as earthing electrode. The size of earth electrode (In case of copper) 2×2 (two foot wide as well as in length) and 1/8 inch thickness.. i.e . 2’ x 2’ x 1/8”. (600x600x300 mm) In case of Iron : 2 ’ x2’ x ¼” = 600x600x6 mm It is recommended to bury the earth electrode in the moisture earth. If it is not possible, then put water in the GI (Galvanized Iron) pipe to make possible the moisture condition. In the earthing system, put the earth electrode in vertical position (underground) as shown in the above fig. Also, put a 1 foot (about 30cm)   layer of powdered charcoal and lime mixture  around the earth plate (earth electrode and earth plate as both are the same thing). This action makes the possible increase in the size of the earth electrode which leads a better continuity in the earth (earthing system) and also helps to maintain the moisture condition around earth plate.

19. Earth Plate or Earth Electrode Size for Small installation In small installation, use metallic rod (diameter = 25mm (1inch) and length = 2m (6ft) instead of earth plate for earthing system. The metallic pipe should be 2 meter below from the surface of ground. To maintain the moister condition, put 25mm (1inch) coal and lime mixture around the earth plate. For effectiveness and convenience, you may use the copper rods 12.5mm (0.5 inch) to 25mm (1 inch) diameter and 4m (12ft) length. We will discuss the installation method of rod earthing latter .

20. Methods of Earthing | Types of Earthing Plate Earthing: In plate earthing system, a plate made up of either copper with dimensions 60cm x 60cm x 3.18mm or galvanized iron (GI) of dimensions 60cm x 60cm x 6.35 mm (2ft x 2ft x ¼ in) is buried vertical in the earth (earth pit) which should not be less than 3m (10ft) from the ground level. Pipe Earthing: A galvanized steel and a perforated pipe of approved length and diameter is placed vertically in a wet soil in this kind of system of earthing. It is the most common system of earthing.

21. Rod Earthing I t is the same method as pipe earthing. A copper rod of 12.5mm (1/2 inch) diameter or 16mm (0.6in) diameter of galvanized steel or hollow section 25mm (1inch) of GI pipe of length above 2.5m (8.2 ft ) are buried in earth Earthing through the Waterman In this method of earthing, the waterman (Galvanized GI) pipes are used for earthing purpose. If stranded conductor is used as earth wire, then clean the end of the strands of the wire and make sure it is in the straight and parallel position which is possible then to connect tightly to the waterman pipe. Strip or Wire Earthing: In this method of earthing, strip electrodes of cross-section not less than 25mm x 1.6mm (1in x 0.06in) is buried in a horizontal trenches of a minimum depth of 0.5m.

22. General method of Earthing / Proper Grounding Installation (Step by Step) The usual method of earthing of electric equipments, devices and appliances are as follow: First of all, dig a 5x5ft (1.5×1.5m) pit about 20-30ft (6-9 meters) in the ground. (Note that, depth and width depends on the nature and structure of the ground) Bury an appropriate (usually 2’ x 2’ x 1/8” (600x600x300 mm) copper plate in that pit in vertical position. Tight earth lead through nut bolts from two different places on earth plate. Use two earth leads with each earth plate (in case of two earth plates) and tight them. To protect the joints from corrosion, put grease around it. Collect all the wires in a metallic pipe from the earth electrode(s). Make sure the pipe is 1ft (30cm) above the surface of the ground. To maintain the moisture condition around the earth plate, put a 1ft (30cm) layer of powdered charcoal (powdered wood coal) and lime mixture around the earth plate of around the earth plate. Use thimble and nut bolts to connect tightly wires to the bed plates of machines. Each machine should be earthed from two different places. The minimum distance between two earth electrodes should be 10 ft (3m). Earth continuity conductor which is connected to the body and metallic parts of all installation should be tightly connected to earth lead. At last (but not least), test the overall earthing system through earth tester. If everything is going about the planning, then fill the pit with soil. The maximum allowable resistance for earthing is 1Ω. If it is more than 1 ohm, then increase the size (not length) of earth lead and earth continuity conductors. Keep the external ends of the pipes open and put the water time to time to maintain the moisture condition around the earth electrode which is important for the better earthing system.

23. ADVANTAGES OF EARTHING The following are the few advantages : Reduced operation & Maintenance cost Improved lightning protection. Simplification of ground fault location. Improved system and equipment fault protection. Improved service reliability Greater safety for personnel & equipment Prompt and consistent operation of protective devices during earth fault.

24. The disadvantages of earthing T he two important disadvantages are: Cost : the provision of a complete system of protective conductors, earth electrodes , etc. is very expensive. Possible safety hazard: It has been argued that complete isolation from earth will prevent shock due to indirect contact because there is no path for the shock current to return to the circuit if the supply earth connection is not made Fig 5.3Danger in an unearthed system a) apparent safety: no obvious path for shock current b) actual danger: shock current via stray resistance and capacitance

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