I wouldn't mind VD becoming a mandatory requirement in the NEC as I do think it is important, however I am not sure it fits into the purpose of the code. Then again, there are many sections of the code which are not exactly a pure life and property safety requirement.
Perhaps they should split the code up into three general categories.
1. MUST DO
2. SHOULD DO
3. CAN DO
Maybe that isn't such a good idea...
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Bryan P. Holland, MCP