Forget the strata manager. Write to the secretary of the Owners Corp and tell them you need access but, if they insist on you calling out an electrician or power company worker, you will be charging them the call-out fee.
Energy companies are increasingly demanding that we do our own meter readings. It is completely unreasonable for strata managers and building managers or caretakers to deny access. Also, in case of emergency, someone in your building should be a registered keyholder.