November 19, 2018


intended to provide information that it is hoped will prove helpful. BS lists five types of earthing system: TN-S, TN-C-S, TT, TN-C, and IT. T = Earth (from the . 29 Mar In an electrical network, an earthing system is a safety measure which against electric shock), an RCD cannot be used in a TN-C system. Types of Earthing Systems, TNC, TNS, TNCS, TT, IT.

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The body of the electrical device is connected with earth via this earth connection at the transformer. The current may be high enough to operate the over current protection fuse or circuit breakerwhich will then interrupt the circuit.

Tall structures may have lightning rods as part of a system to protect them from lightning strikes. This electrode may or may not be syxtem independent of the source electrode. Capacitive impedance is never used.

This is the simplest way I can put it without going into extended detail. It earthlng, however, the effect of slightly increasing the first-fault current level.

TT The main earth cable from the met is connect to an earth electrode aka earth rod. In other projects Wikimedia Commons. Protection against electric shocks and electrical fires. Connection to the LV utility distribution network. However, in practice, the fault current will not be equal to zero: Earthing conductors previously termed earth leads earthingg be checked for compliance with the IEE Regulations, i.

Earth leakage circuit breakers are used for the purpose. Do you already have an account? As a result, ground fault currents have no path to be closed and systm have negligible magnitudes. Electrical Engineer’s Reference Book. The second letter denotes the consumer.

And the IT system requires that the PE is the same for all receivers if the PE syshem not common to all receivers must be set to medium sensitivity differential protection on each departure.


The two zones of influence may overlap without affecting the operation of protective devices. Characteristics of particular sources and loads. Amjad Aug 14, This information must be requested early. The protective conductors previously known as earth continuity conductors must also comply with BS the IEE Regulations and in general for phase conductors of less than 16 mm 2 ; this means the protective conductors must be the same size as the phase conductors. This page was last modified on 19 Juneat Now that we’ve seen some prity diagrams am I starting to sound like a teacher lol we will now look at real world photos that are not as straight forward as the diagrams.

High resistance grounding system grounds the neutral through a resistance which limits the ground fault current to a value equal to or slightly greater than the capacitive charging current of that system. The neutral and the earthed parts are only connected together via an electrode system back to the source earth and neutral.

Lastly there eafthing the TT system which uses mother earth as part of the earth return. If the main earth cable doesn’t go back to the fuse or incoming cable it will be a TT.

Can you explain the common earthing systems TN-S, TN-C

In a TT Terra-Terra earthing system, the protective earth connection for the consumer is provided by a local earth electrode, sometimes referred to as the Terra-Firma connection and there is another independently installed at the generator.

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Two PE conductors are separate from a distance of 8m. TN-S You can clearly see the main earth cable connected to the ‘S’heath. The Electricity Distributor should be able to give the fault level or the equivalent impedance of the supply network and the manufacturer can provide the appropriate impedances for the transformer. Hello, Thanks for the great efforts on EEP! The reasons for this form of power-source earthing are to fix the potential of a small network with respect to earth Zs is small compared to the leakage impedance and to reduce the level of overvoltages, such as transmitted surges from the MV windings, static charges, etc.


In the IT system it is because common to all receivers PE a short-circuit may establish and solicited devices magnetic protection.

Earthing system

In industrial applications, earth leakage relays are used with separate core balanced current transformers. In the TN-C-S system, the TN-C 4 wires system must never be used downstream of the TN-S 5 wires system, since any accidental interruption in the neutral on the upstream part would lead to an interruption in the protective conductor in the downstream part and therefore a danger.

This is the risk of mechanical failure of the electrical conductor. Regulations may identify special cases for earthing in mines, in patient care areas, or in hazardous areas of industrial plants. The k factor takes into account the resistivity, temperature coefficient and heat capacity gnc the conductor materials and of tcn initial and final temperatures. For example, the sheaths on some underground cables corrode and stop providing good earth connections, and so homes where high resistance “bad earths” are found may be converted to Tmc.

Connection to the MV utility distribution network. In a TN-S earthing system can the neutral conductor disconnected simultaneously with the 3 phases?

When the phase conductor is above 16 mm 2 then the protective conductor may remain at 16 mm 2 until the phase conductor is 35 mm 2after which the protective conductor should be half systeem size of the phase conductor.