IEC 60420:1990

Committees responsible
Specification
1 General
2 Normal and special service conditions
3 Definitions
4 Rating
5 Design and construction
6 Type tests
7 Routine tests
8 Application guide for the selection of switch-fuse
      combinations for service
9 Information to be given with enquiries, tenders
      and orders
10 Rules for transport, storage, erection and
      maintenance
Appendices
A Example of the co-ordination of fuses, switch and
      transformer
B Justification of the procedure for determining
      transfer current and of the parameters associated
      with test duty 4
Tables
I Standard values of rated TRV (Based on practice in
      Europe)
IA Standard values of rated TRV (Based on practice in
      the United States of America and Canada)
II Nameplate markings
III Standard values of prospective TRV for test duty 2
      (Based on practice in Europe)
IIIA Standard values of prospective TRV for test duty 2
      (Based on practice in the United States of America
      and Canada)
IV Standard values of prospective TRV for test duty 4
      (Based on practice in Europe)
IVA Standard values of prospective TRV for test duty 4
      (Based on practice in the United States of America
      and Canada)
V Summary of test parameters for test duties 1 to 5
Figures
1 Representation of a specified TRV by a two-
      parameter reference line and a delay line
2 Example of a two-parameter reference line for a
      TRV
3 Arrangement of test circuits for test duties 1 and
      2
4 Arrangement of test circuits for test duty 3
5 Arrangement of test circuits for test duties 4 and
      5
6 Determination of power-frequency recovery voltage
7 Practical determination of transfer current
8 Probable maximum and minimum time-current
      characteristics of fuse
9 Transfer current in relation to the primary fault
      current Isc due to a solid short in the
      transformer secondary terminal
10 Characteristics relating to the protection of an
      11 kV - 400 kVA transformer
11 Discrimination between HV and LV fuses
12 Characteristics for determining take-over current

This standard applies to three-pole units for public and industrial distribution systems which are functional assemblies of switches including switch-disconnectors and current-limiting fuses and thus able to interrupt: -any load current up to the rated breaking current of the switch; -any over-current up to the rated short-circuit breaking current of the combination by which automatic interruption is initiated. This standard applies to combinations designed with rated voltages above 1 kV and below 52 kV for use on three-phase alternating current systems of either 50 Hz or 60 Hz.