TN-C-S system

TN-C-S system Neutral and protective functions combined in a single conductor in a part of the system ... 

Figure 3.35 Protective multiple earthing supply (TN-C-S system) showing earthing and bonding...

Although the electricity supply companies have converted a substantial number of TT systems to TN-C-S systems, some TT systems are still in use, mostly in rural areas where it is often difficult or impracticable to obtain and maintain a low earth loop impedance. In these cases, the overcurrent protection should be supplemented by RCD protection as required in Regulations 413-02-18 to 20 and 471-08-06. 

Regulation 542-01-04 is about TT earthing systems. They are mostly found in rural areas with overhead supply lines. The consumer is required to provide his own earth and generally an RCD for earth leakage protection. There is an ongoing programme to convert TT to TN-C-S systems and to provide a CNE terminal for the consumer s use for earthing purposes instead of his earth electrode. 

As an example, in TN-C-S supplies to domestic premises a break in the combined neutral/earth (CNE) conductor of an overhead service line would cause the metalwork in the premises to become live at or about the supply voltage if any apparatus, such as a dishwasher, were to be connected and switched on. To prevent this type of hazard, the integrity of the CNE conductor, throughout the system, has to be maintained, so all joints have to be properly made and reliable, and fuses and solid state devices are prohibited in these conductors. 

Part 2 provides an extensive list of definitions of terms used throughout the standard. One definition that needs to be clarified is that of the earthing arrangements. There are four descriptors in general use which are used both in BS 7671 and in this book. They are TN-S, TN-C-S, TT and IT systems. In these abbreviations, the letters have the following meanings ... 

In caravan parks, the distribution system should comply with the relevant parts of the Electricity Supply Regulations 1988 as well as with the Division Two requirements. Regulation 608-13-05 could perhaps have been improved by indicating that for TN-S supplies the supply company will normally provide an earthing facility, but for TN-C-S (PME) and TT supplies an earth electrode has to be installed by the occupier. The section requires the supply socket outlets to have sensitive RCD protection complying with subsection 412-06, as for the caravan installations, so that in the event of an earth fault in a caravan both RCDs should operate. To avoid more than the faulty installation supply being disconnected, grouping should be avoided and an RCD provided for each socket outlet. 

Janke, C.J., Dorsey, G.F., Havens, S.J. and Lopata, V.J., Toughened epoxy resins eured by eleetron beam radiation. 28th International SAMPE Technical Conference, S71, 1996. Janke, C.J., Electron beam curable cationic epoxy resin systems and composites. 1st Annual Electron Beam Curing of Composites Workshop, September 18-19, Oak Ridge, TN, Ref. ID, 1996. 

The substances H S, C02 and (C Hj-UO (diethyl ether) were treated as slightly active as there afen ndications that with these compounds cross-association occurs in liquid water. In the case of diethyl ether this conclusion is supported by the considerably higher mutual solubility for the H-O- -HgJgO system compared with water-alkane systems as shown Tn Table 5. To keep the number of parameters low, the following procedure was adopted in accounting for cross-association ... 

Figure S shows the MWD produced in a zero-one-two system where values of the various rate coeRicients have been chosen to give a MWD dominated by transfer and exit p = 0-1 sec , k = 0.3 sec", / = 0.9 sec" , c = 0 sec". This gives a steady state n of 0.34. Before discussing the form of the curves, we pause to consider the axes employed in this figure. Because we are considering a steady state system, we may use as abscissa either M (molecular weight, in a.tn.u.) or r (growth time, in s). We use buth...

Berezhnoi a. S., Multicomponent Oxide Systems (tn Russian), Naukova dumka, Kiev, 1970 (BepeacHoii A. C., MyjiTHKoMnoHeHTHbie cMCxeMbi okhcjtob, HayKosafl /(ywica, Khbb). 

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