Also if you have an outlet with an RCD I would use that.

That's how I do it it's 12v you will be fine. Only issue is if there is some kind of dead short in the powersuply and you get 230v though the wires but I highly doubt that would happen. If your that worried about it see if you can get alligator clips for your multi meter. Or some other way of testing it without actually touching the wires.