Is the approval by the Public Utility Commission of the sale, encumbrance or lease of property is a condition precedent to the validity of a contract?

No. While in the old law the sale without the approval of the Public Utility Commission was declared null and void, under Commonwealth Act 146, the new law, the sale may not only be negotiated but completed before said approval. In other words, the approval by the Commission is not a condition precedent to the validity of the contract. The approval is only necessary to protect public interest (Darang vs. Belizar, G.R. No. L-19487, January 31, 1967).