Welcome to the forum, I have merged your two posts together that relate to the same question. Posting duplicates just clutters the forum and makes is difficult for others to follow the various topics.
re your question, your Vd calculation using the mv/a/m & length values are only useful if you know what the cable CSA is and the length of the cable run. But neither of these details have been given in the question. Do you have a copy of guidance note 3, to read what that suggests about verifying volt-drop during a periodic inspection? You do know the resistance of the circuit conductors, and you know the current which flows through those conductors, and through the unknown size of load connected in series with the supply conductors.