29-06-2012, 12:09 PM
EARTHING SCHEMES
[attachment=26060]
MEANING OF EARTHING SYSTEMS
I T SYSTEM :
* Isolated or impedance earthed neuteal.
* IT system (isolated neutral) No intentional connection is made between the neutral point of the supply source and earth. Exposed- and extraneous-conductive-parts of the installation are connected to an earth electrode.
CHARACTERISTICS OF T T SCHEME
Simplest solution to design and install.
Does not required continuous monitoring.
Protection is ensured by special devices.
Each insulation parts results in an interruption in the supply.
Loads or parts of the installation which, during normal operation, cause high leakage currents. So required special measure to take to avoid continuous tripping.
CHARACTERISTICS OF T N SCHEME
Requires the Installation of earth electrodes at regular intervals.
Requires that the initial check on effective tripping at begin or installation period.
Requires that any modification, extension, designed & carried out by qualified electrician.
Damage to the winding of rotating machines.
May, risk of fire.
[attachment=26060]
MEANING OF EARTHING SYSTEMS
I T SYSTEM :
* Isolated or impedance earthed neuteal.
* IT system (isolated neutral) No intentional connection is made between the neutral point of the supply source and earth. Exposed- and extraneous-conductive-parts of the installation are connected to an earth electrode.
CHARACTERISTICS OF T T SCHEME
Simplest solution to design and install.
Does not required continuous monitoring.
Protection is ensured by special devices.
Each insulation parts results in an interruption in the supply.
Loads or parts of the installation which, during normal operation, cause high leakage currents. So required special measure to take to avoid continuous tripping.
CHARACTERISTICS OF T N SCHEME
Requires the Installation of earth electrodes at regular intervals.
Requires that the initial check on effective tripping at begin or installation period.
Requires that any modification, extension, designed & carried out by qualified electrician.
Damage to the winding of rotating machines.
May, risk of fire.