A method of detecting an electric stray current through a main bearing of a rotating system comprising: a main shaft; a bearing housing attached to a metallic structure; and a main bearing having an inner ring attached to the main shaft and an outer ring attached to the bearing housing, said method comprising the steps of: providing a first measurement device for determining a measure indicative of an electric current in said main shaft at a first location on a side of said main bearing; providing a second measurement device for determining a measure indicative of an electric current in said main shaft at a second location on a side of said main bearing; and determining a measure indicative of a difference between a first electric current flowing through said main shaft at said first location and a second electric current flowing through said main shaft at said second location, said difference being indicative of said electrical stray current through said main bearing, characterized in that, the rotating system further comprising: a hub; a plurality of blades (104a, 104b) connected to the hub; at least one electrical motor arranged at the hub; the main shaft being attached to the hub and enclosing cabling for providing electrical power to said at least one electrical motor at the hub; the metallic structure is acting as electrical earth; and wherein the first measurement device is facing said hub and the second measurement device is facing away from said hub. a main shaft; a bearing housing attached to a metallic structure; and a main bearing having an inner ring attached to the main shaft and an outer ring attached to the bearing housing, said method comprising the steps of: providing a first measurement device for determining a measure indicative of an electric current in said main shaft at a first location on a side of said main bearing; providing a second measurement device for determining a measure indicative of an electric current in said main shaft at a second location on a side of said main bearing; and determining a measure indicative of a difference between a first electric current flowing through said main shaft at said first location and a second electric current flowing through said main shaft at said second location, said difference being indicative of said electrical stray current through said main bearing, characterized in that, the rotating system further comprising: a hub; a plurality of blades (104a, 104b) connected to the hub; at least one electrical motor arranged at the hub; the main shaft being attached to the hub and enclosing cabling for providing electrical power to said at least one electrical motor at the hub; the metallic structure is acting as electrical earth; and wherein the first measurement device is facing said hub and the second measurement device is facing away from said hub. providing a first measurement device for determining a measure indicative of an electric current in said main shaft at a first location on a side of said main bearing; providing a second measurement device for determining a measure indicative of an electric current in said main shaft at a second location on a side of said main bearing; and determining a measure indicative of a difference between a first electric current flowing through said main shaft at said first location and a second electric current flowing through said main shaft at said second location, said difference being indicative of said electrical stray current through said main bearing, characterized in that, the rotating system further comprising: a hub; a plurality of blades (104a, 104b) connected to the hub; at least one electrical motor arranged at the hub; the main shaft being attached to the hub and enclosing cabling for providing electrical power to said at least one electrical motor at the hub; the metallic structure is acting as electrical earth; and wherein the first measurement device is facing said hub and the second measurement device is facing away from said hub. a hub; a plurality of blades (104a, 104b) connected to the hub; at least one electrical motor arranged at the hub; the main shaft being attached to the hub and enclosing cabling for providing electrical power to said at least one electrical motor at the hub; the metallic structure is acting as electrical earth; and wherein the first measurement device is facing said hub and the second measurement device is facing away from said hub.