portion of it is super-imposed on, and a part of whose weight is borne by, that motor vehicle. Therefore, every instrument including ploughing machine or curshing attached to a tractor will not necessarily be a trailer. At the highest, it can be a semi-trailer. Even assuming that the said two categories of equipment are semitrailers, the same are not the motor vehicle covered by clause (28) of section 2 of the MV Act. Since a semi-trailer is not a motor vehicle, the provisions of Section 147 of the MV Act deals with insurance of motor vehicles. Even assuming that it is an attachment to the tractor, it is not required to be covered by a statutory policy of insurance as such attachments are not motor vehicles. In view of sub-clauses (a) to (c) of clause (i) of proviso to sub-section (1) of section 147 of the MV Act, the liability of employees working on such instruments like ploughing machine or crushing machine attached to a tractor is not required to be covered by a policy of insurance in respect of a tractor issued in terms of sub-section (1) of section 147 of the MV Act."