Earthing systems across the world and their significance

Tushar Panchal
Master in Power and Energy Systems
NJIT
Newark, NJ, US tnp24@njit.edu Abstract— The paper focuses on various earthing systems across North America and across the world. It talks briefly about the standards and practices followed across the world. It gives a detailed insight about the methods of earthing (grounding) in United States under the NEC. It then talks about the TT, TN and IT systems of grounding, their main advantages and characteristics and the methods of protection applied in each system. The IEC 60364 defines the standards and practices necessary for these systems for the other countries around the world. In the end, the paper also tries to give readers a brief insight about the residual current devices.
I. objective
The main purpose of earthing is to protect personnel from shocks and serious fatal conditions to improve the reliability of the system and ensure continuous service. It is used to control voltage to ground within predictable limits. Proper installation of grounding systems facilitate the removal of hazardous fault currents from flowing uncontrollably into the earth by using protecting devices. This time is extremely short as compared with continuously flowing uncontrolled stray current. There are advantages and disadvantages for every earthing system. In addition, proper earthing will also conduct and convey lightning currents.
II. applicable standards
A. North American grounding methods.
1. NFPA 70, the 2005 NEC, Article 250
2. IEEE Green Book; IEEE Std. 142; Recommended Practice for Grounding of Industrial and Commercial Power Systems
3. CSA C22.1, Canadian Electrical Code, Part 1, Safety Standards for Electrical Installations, Section 10, Grounding and Bonding
B. International grounding methods
1. IEC 60364
2. IEC 60079-14 (Hazardous Locations)
3. AS 3007.2 – 2004

A. NORTH AMERICAN GROUNDING METHODS
Article 250 of NFPA 70 (National Fire Protection Association) of the 2008 National Electric Code,stands as the basis for grounding in the United States and many other countries around the world.
a. Definition of grounding as per National Electrical Code Article 250
2. Effective Ground-Fault Current Path: An intentionally constructed, low-impedance electrically conductive path designed and intended to carry current underground-fault conditions from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground fault detectors on high-impedance grounded systems.
3. Ground Fault: An unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally non-current carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.
4. Electrical System Grounding: Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.
5. Grounding of Electrical Equipment: Normally noncurrent carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials.
b. Types of Common Grounding Methods
1. Solid Grounding: In solidly grounded systems there is no intentional resistance provided from neutral to ground. Such kinds of systems are usually used for low voltage applications.(see Fig.1)

Fig. 1(solidly grounded system)

2. Low Resistance Grounding: In these systems a small resistance is intentionally inserted between the ground the neutral to limit the ground fault current between 100 to 1000 amps when one phase is grounded.(see Fig. 2)

Fig. 2(low resistance grounded system)

3. High Resistance Grounding: In these systems the resistance is