Replace the existing first paragraph by the following: This part of IEC 60947 series applies to circuit-breakers, intended to be installed and operated by instructed or skilled persons only, the main contacts of which are intended to be connected to circuits, the rated voltage of which does not exceed 1 000 V a.c. or 1 500 V d.c.; it also contains additional requirements for integrally fused circuit-breakers. Replace the 16th existing paragraph by the following: For certain specific applications (for example traction, rolling mills, marine service, downstream of variable frequency drives, use in explosive atmospheres) particular or additional requirements may be necessary.