not entirely true flameport..
if I decided to open a shop and then later decided to add a ring main and a new sub main CU I could do it myself since I have the knowledge and experience to do it.. I wouldn't HAVE to employ a sparky to do it..
however I see the point you were trying to make..
as the OP has neither the understanding or experience to do it he's BEST OFF getting a sparky to do it as it will likely be safer if he does..
How do we know this? It may be that he can do the work himself - after all he has asked a relatively intelligent question (spelling aside!) regarding the requirement of a sub main.
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