Exposed live parts not covered by potting materials etc. and insulating materials holding them, which may give rise to fire and smoke emission hazards owing to deterioration in the insulation caused by accumulated dust and dirt or by dew condensation during long-term use, shall be constructed in such a way to incorporate measures against the accumulation of dust and dirt and dew condensation during long-term use, in order to prevent smoke emission, ignition and fire hazards.