INTRODUCTION
The installation rules, especially the measures to be applied for protection against electric shock, depend on the value of the voltage used. Since it is neither possible nor necessary to consider each individual voltage value occurring in practical application, common requirements are established for each particular voltage band. This recommendation is intended to furnish the basis for the uniform fixing of such voltage bands.
Within the field of the installations to which IEC Technical Committee No. 64 recommendations are applicable (see Sub-clause 11.2 of GB 16895.11]), it is possible to define two voltage bands which are covered respectively by their own rules.
Some of the conditions to be prescribed may, however, vary as a function of the voltage even within the same voltage band. It is therefore necessary to introduce additional limits for particular applications or installations (e.g. welding, electroplating, etc.). It is assumed, however, that this applies only to a few of the requirements to be fixed. Such specific voltage limits are given in the relevant requirements.
Band I
Band I covers:
— installations where protection against shock is provided under certain conditions by the value of voltage;
— installations where the voltage is limited for operational reasons (e.g. telecommunications, signalling, bell, control and alarm installations).
Band II
Band II contains the voltages for supplies to household, commercial and industrial installations.
This band contains all the voltages of public distribution systems in the various countries.
Explanation of Adoption
1] GB 16895.1-1997 Electrical installations of buildings—Part 1: Scope, object and fundamental principles is identical to IEC 60364-1:1992 Electrical installations of buildings Part 1: Scope, object and fundamental principles.
1. Scope
This recommendation applies to a.c. electrical installations of buildings supplied at a frequency not exceeding 60 Hz and at a nominal voltage up to and including 1 000 V, and d.c . electrical installations of buildings supplied at a nominal voltage (power source) up to and including 1 500 V.
The voltage bands defined are intended mainly for use in connection with installation rules, but may also be used when preparing requirements for electrical equipment.
Note. — The extension of the scope to include frequencies higher than 60 Hz is under consideration.
2. Definitions
The following definitions are adopted in this standard.
2.1 Nominal voltage
Voltage by which an installation (or a part of an installation) is designated.
Notes 1. — The actual value of the voltage in the installation may differ from the nominal voltage by a quantity within normal tolerances.
2. — Voltage transients, such as those due to switching, or temporary voltage variations due to abnormal operation, such as those due to fault conditions in the system supplying the installation, are not taken into consideration.
2.2 Earthed systems
Systems in which a point — generally the neutral point — is directly connected to earth without any intentional impedance.
2.3 Isolated or not effectively earthed systems
Systems in which no point is connected to earth or in which a point — generally the neutral point — is connected to earth by a limiting impedance.
3. A.C Voltage bands
A.C voltage bands in which the installations shall be classified according to their nominal voltage are given in Table 1:
— for earthed systems, by the r.m.s. values of the voltages between phase and earth and between phases;
— for isolated or not effectively earthed systems , by the r.m.s. value of the voltage between phases.
