No public service company shall sell, lease, assign or otherwise dispose of the whole or any part of its franchises, properties or facilities whatsoever, which are necessary or useful in the performance of its duties to the public, and no public service company shall, by any means whatsoever, directly or indirectly, merge or consolidate any of its franchises, properties or facilities with any other public service company, without having secured from the commission an order authorizing it so to do: PROVIDED, That this section shall not apply to any sale, lease, assignment or other disposal of such franchises, properties or facilities to a public utility district.