Lines company Delta Utility Services is investigating a faulty cable switch thought to be responsible for cutting power to 108 businesses in Shotover St, Beach St and Queenstown Wharf on Tuesday.
The outage plunged many businesses into darkness, deterring customers and prompting Beach St's Central Art Gallery to guide patrons by torchlight.
Delta operations manager Lindsay McLennan said a circuit breaker was activated, cutting electricity at 9.01am.
By 10.23am, 84 customers had power restored. The remaining 24 premises regained power by 1.20pm - 19 minutes longer than Delta's "target restoration time" of four hours.
Mr McLennan said any businesses that had still been without power after 1pm should contact their electricity retailer if they had any inquiries about loss-of-business compensation.
He said the fault was under investigation and it could take up to three weeks to establish which underground switch in the network of three waterfront substations was the problem.
