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A Master Electrician here to help. I am a double qualified; USA & UK electrician. Please give me a moment to formulate a reply.
Beow is the only NEC reference to this;
D) Boxes at Ceiling-Suspended (Paddle) Fan Outlets. Outlet boxes or outlet box systems used as the sole support of a ceiling-suspended (paddle) fan shall be listed, shall be marked by their manufacturer as suitable for this purpose, and shall not support ceiling-suspended (paddle) fans that weigh more than 32 kg (70 lb). For outlet boxes or outlet box systems designed to support ceiling-suspended (paddle) fans that weigh more than 16 kg (35 lb), the required marking shall include the maximum weight to be supported.
Your answer addressed ceiling fans not lighting fixtures. Is there any requirement to provide a safety cable for a lighting fixture if it weighs over a certain amount?
I can find no reference to this in the NEC. I shall pass your question to an electrical inspector but as I say I find no reference except to ceiling fans. Although I am sure manufacturers will have their own safety requirements in which case you will be obliged to follow them.
He may not be online until this evening.