From November 1st until the first Sunday after the 2nd Easter day, all vehicles with a permissible total weight over 3500 kg are required to carry chains.
This is always applicable if you are driving on roads with snow and ice. For the three northernmost counties, these requirements apply from October 15th to April 30th.

During the same period, the vehicle must have approved winter tires with at least a 5 mm tread depth (see rules below).
However, chains must also be carried, regardless of road conditions.
The chains must fit the vehicle’s wheels and at all times provide contact between the chain and the road surface.
They should be made of metal/steel, be suitable for the conditions, and withstand the strain of the loading.