Ice sleeves are tubes of ice created due to wet snow - snowflakes with high water content. This type of snow can be found in various geographic areas, from northern Europe to the United States to Japan, at temperatures near freezing and with low wind speed.
When the wind blows, wet snow may stick to the conductor, the wire through which electricity passes, causing it to rotate. As the snow solidifies, it creates the ice sleeve. This mechanism can lead to the formation of a coating of frozen snow up to 10 times the diameter of the conductor. The weight borne by the span, the electrical wire which connects two pylons, can be significantly increased by even thousands of kilos, in extreme cases leading to damage to the conductors, shield wires and supports.