Work on fixed installations (faste installationer) has to be done by an autoriseret elinstallatørvirksomhed (authorised electrical firm). Ask whether they hold the authorisation themselves or bring someone who does, and get that on the invoice.
Aalborg and Nørresundby sit on either side of the fjord. Jobs in Aalborg Øst and SV are often houses. The centre is apartments and older stairwells. The same 1 businesses as the Danish page: Aut El-installatør Jens Melgaard.