Such a connection (a buried metal structure) is required to provide protective earth in IT and TT systems. In single-ended single-phase systems where the Earth and neutral are combined (TN-C, and the part of TN-C-S systems which uses a combined neutral and earth core), if there is a contact problem in the PEN conductor, then all parts of the earthing system beyond the break will rise to the potential of the L conductor. Such a rise in the potential of the neutral beyond the break is known as a neutral inversion. Worse, in a multi-phase system, if one of the line conductors made contact with earth, it would cause the other phase cores to rise to the phase-phase voltage relative to earth rather than the phase-neutral voltage. Naraina, New Delhi A-39, Phase II, Naraina Industrial Area, Naraina, New Delhi - 110028, Dist. Thane Unit No.9, Tirupati Trade Center, Navghar, Navghar,vasai, Vasai East, Palghar - 401210, Dist. In this case, a single mechanical and electrical system can be used to connect together many of the system components, or in some cases, all of them.
In IT systems, a single insulation fault is unlikely to cause dangerous currents to flow through a human body in contact with earth, because no low-impedance circuit exists for such a current to flow. In IT and TN-C networks, residual current devices are far less likely to detect an insulation fault. The neutral earthing resistor is monitored to detect an interrupted ground connection and to shut off power if a fault is detected. TT networks require proper RCD (Ground fault interrupter) protection. The UG product can be installed below ground to seal cables entering through the foundation of electrical substations and shelters, as proven by UG test standards. This is used in the trailing cables of mining machinery. Separate conductors for overhead lines and armoring of cables are used for earth connection. Neutral and earth conductors run separately on overhead distribution lines. TN networks save the cost of a low-impedance earth connection at the site of each consumer. TN-C networks save the cost of an additional conductor needed for separate N and PE connections. Since it is unsafe to do this in a TN-C system, RCDs on TN-C should be wired to only interrupt the line conductor.
Also, RCDs usually isolate the neutral core. In a TN-C system, they would also be very vulnerable to unwanted triggering from contact between earth conductors of circuits on different RCDs or with real ground, thus making their use impracticable. To avoid accidental shock, current sensing circuits are used at the source to isolate the power when leakage current exceeds a certain limit. Since the earth leakage is restricted, leakage protection devices can be set to less than 750 mA. A separate pilot wire is run from distribution/ equipment supply system in addition to earth wire, to supervise the continuity of the wire. The result was that the bus speeds were now very much slower than what a modern system needed, and the machines were left starved for data. In TN-S and TT systems, the consumer has a low-noise connection to earth, which does not suffer from the voltage that appears on the N conductor as a result of the return currents and the impedance of that conductor. Earlier TT installations may lack this important safety feature, allowing the CPC (Circuit Protective Conductor or PE) and perhaps associated metallic parts within reach of persons (exposed-conductive-parts and extraneous-conductive-parts) to become energized for extended periods under fault conditions, which is a real danger.
In an unbalanced multi-phase system, busbar machine the potential of the earthing system will move towards that of the most loaded line conductor. A resistance earth system is used for mining in India as per Central Electricity Authority Regulations. Due to the (small) risks of the lost neutral raising 'earthed' metal work to a dangerous potential, coupled with the increased shock risk from proximity to good contact with true earth, the use of TN-C-S supplies is banned in the UK for caravan sites and shore supply to boats, and strongly discouraged for use on farms and outdoor building sites, and in such cases it is recommended to make all outdoor wiring TT with RCD and a separate earth electrode. If you use an inverter then it is recommended to connect the staircase light to the inverter power supply. If you use a very high-power inverter and batteries that can drive all the loads of your home then you can connect the inverter just after the main switch. The neutral must be connected to earth only on the supply side of the customer's disconnecting switch. In industrial applications, earth leakage relays are used with separate core balanced current transformers. In the United States National Electrical Code and Canadian Electrical Code, the feed from the distribution transformer uses a combined neutral and grounding conductor, but within the structure separate neutral and protective earth conductors are used (TN-C-S).
