Mr Marsh said it was less common for thieves to target urban areas,, and tampering with the network in highly populated areas posed a risk to more people.
He said Powerco's field staff and electricity consumers were put at risk of serious shock or even electrocution.
"Powerco has acted to make the network safe and we have people out looking to identify if any other parts of the network have been damaged by these thieves, who are looking to make a few quick bucks."
Mr Marsh urged members of the public to be vigilant and report suspicious behaviour, either to Powerco on 0800 769 372 or to police.