There could be another massive power cut to tens of thousands of Northland homes and businesses, the region's lines company has warned today.
Top Energy says it has found what it thinks caused Friday's power cuts, that left 30,000 customers without power for several hours.
A faulty insulator in the Kaikohe substation, which Top Energy bought off the grid operator Transpower in 2012, is thought to be the problem.
The company admitted there would be another massive cut to the entire Mid and Far North areas if the insulator failed a second time.
Chief executive Russell Shaw said it started work with Transpower this afternoon to try to fix the faulty equipment.
"We acquired these assets from Transpower at the end of their life-span and in very poor condition, precisely because we felt they were a priority for the security of the electricity supply in our region."
Friday's massive power cut left business owners irate, with complaints that cuts were all too common in the Far North.
But the investigations have revealed how big a potential problem the suspected faulty insulator could cause.
"Over the past 12 months alone we have spent $5 million on upgrading this particular asset.
"It's frustrating that we hadn't yet replaced the piece of kit which likely caused Friday's outage," Mr Shaw said in a statement.
Top Energy said would try to fix the equipment without disrupting power supplies.