The US National Electric code defines <50V as low voltage but UL defines anything over 20V as high voltage. UL generally deals with products so that is probabl

The US National Electric code defines <50V as low voltage but UL defines anything over 20V as high voltage. UL generally deals with products so that is probably why they are more conservative. Picture a baby sucking on something and you can imagine why they want anything over 20V to be double insulated. If car manufactures want to comply with UL standards that would mean they would no longer be able to use the car's frame for the current return path.