I went to a friends house the other day to see his new kitchen, in the process of this he has had a new CU fitted... the electrician has fitted new meter tails (blue, brown) in 25mm cable. The problem is that it is not the normal grey double insulated tails you see. Instead it is what looks like blue and brown tri-rated cable. Is this normal? I have seen a few pictures on the internet with blue and brown tails.