Earthing arrangements

The earthing arrangements of the generator neutral. The control of the excitation of the generator when operating in either isolated or parallel mode. 

Visual inspection of signal shielding and earthing arrangements to eliminate noisy signals. Continuity checks on earth bonding. 

Neutral earthing arrangements, e.g. solid, with a neutral earthing resistance (NER), with a common busbar, switches or circuit breakers for isolation. 

Find the most appropriate cable and fuses for the motor. Determine whether or not an earth leakage current relay should be used at the motor control centre. Assume a TN earthing arrangement. 

Let us first define some of the words we will be using. Chapter 54 of the lET Regulations describes the earthing arrangements for an electrical installation. It gives the following definitions ... 

Other items of equipment at this position are the energy meter and the consumer s distribution unit, providing the protection for the final circuits and the earthing arrangements for the installation. 

The supply earthing arrangements are indicated by the first letter, where T means one or more points of the supply are directly connected to earth and I means the supply is not earthed or one point is earthed through a fault-limiting impedance. 

The installation earthing arrangements are indicated by the second letter, where T means the exposed conductive parts are connected directly to earth and N... 

Where the circuit inciudes electronic equipment which might be damaged by the insulation resistance test, a measurement between all live conductors (i.e. live and neutral conductors connected together) and the earthing arrangements may be made. The insulation resistance of these tests should be not less than 1. OMH (lET Regulation 612.3.3). 

Low-voltage supplies having earthing arrangements which are independent of the supply cable are classified as TT systems. For this type of supply it is necessary to sink an earth electrode into the general mass of earth, which then forms a part of the earth return in conjimction with an RCD. 

An electricity supply in which the earthing arrangements must be... 

Part II addresses protection and earthing arrangements. The protection requirements are non-prescriptive and relate to precautions, such as the provision of fuses and circuit breakers, against excess current and earth leakage currents causing damage. 

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 ... 

One of the first considerations for the designer is to determine the nature or characteristics of the supply and the earthing arrangements. Inspection of the existing supply or by requesting details from the supply distributor will be necessary to determine ... 

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