IEC 60947-3-2015 pdf free download.Low-voltage switchgear and controlgear – Part 3: Switches, disconnectors, switch-disconnectors and fuse-combination units.
4.3.2 Currents
An equipment is defined by the following currents.
4.3.2.1 Conventional free air thermal current (Ith) Subclause 4.3.2.1 of IEC 60947-1 applies.
4.3.2.2 ConventIonal enclosed thermal current (‘the) Subclause 4.3.2.2 of IEC 60947-1 applies.
4.3.2.3 Rated operational currents (le) (or rated operational powers) Subclause 4.3.2.3 of IEC 60947-1 applies.
4.3.2.4 Rated uninterrupted current (Ia) Subclause 4.3.2.4 of IEC 60947-1 applies.
4.3.3 Rated frequency
Subclause 4.3.3 of IEC 60947-1 applies.
4.3.4 Rated duty
The rated duties considered as normal are as follows.
4.3.4.1 Eight-hour duty
Subclause 4.3.4.1 of IEC 60947-1 applies.
4.3.4.2 UnInterrupted duty
Subclause 4.3.4.2 of IEC 60947-1 applies.
4.3.5 Normal load and overload characteristics
4.3.5.1 Ability to withstand motor switching overload currents
See Annex A.
4.3.5.2 Rated making capacity
Subclause 4.3.5.2 of IEC 60947-1 applies with the following additions.
The rated making capacity is stated by reference to the rated operational voltage and rated operational current and to the utilization category according to Table 3.
Not applicable to AC-20 or DC-20 equipment.
4.3.5.3 Rated breaking capacity
Subclause 4.3.5.3 of IEC 60947-1 applies with the following additions.
The rated breaking capacity is stated by reference to the rated operational voltage and rated operational current and to the utilization category according to Table 3. Not applicable to AC-20 or DC-20 equipment.
4.3.6 Short-circuit characteristics 4.3.6.1 Rated short-time withstand current (/cw) The rated short-time withstand current of a switch, a disconnector or a switch-disconnector is the value of short-time withstand current, assigned by the manufacturer, that the equipment can carry without any damage under the test conditions of 8.3.5.1. The value of the rated short-time withstand current shall be not less than twelve times the maximum rated operational current and, unless otherwise stated by the manufacturer, the duration of the current shall be 1 s. For a.c., the value of the current is the r.m.s. value of the a.c. component and it is assumed that the highest peak value likely to occur does not exceed n times this r.m.s. value, the factor n being given by Table 16 of IEC 60947-1.IEC 60947-3 pdf download.