Police have busted a sophisticated copper-stealing ring which left innocent people at risk of electrocution when tens of thousands of dollars worth of the metal was taken from power poles across Waikato.

A group of at least seven people dressed in high-visibility clothing drove to different power poles every night to get the copper from earth cables.

They were skilled enough to know how to cut the cable straps without injuring themselves, Hamilton police area commander Inspector Greg Nicholls said.

"They would go out almost nightly to plunder the electricity networks."


However, police began closing in when power company WEL Networks discovered the extensive damage during routine checks.

Earth cables perform an essential safety function by allowing the electricity to earth to the ground if the power supply becomes overloaded.

Without them, the electricity would travel to the next available earthing source, usually a house or cow shed, making it live and putting the owners at risk of electrocution, said Acting Detective Senior Sergeant Neville Ross of the Hamilton tactical crime unit.

The copper from the cables can be sold to scrap-metal dealers for up to $10 a kilogram.

Mr Ross said seven people had been arrested after the investigation into the large-scale operation.

A 17-year-old was arrested in Kaikohe on Tuesday and faces up to 40 representative charges of criminal damage.

"Our inquiries into this man follow the arrest last week of six people at four addresses in Hamilton and South Auckland in which about $1000 worth of copper was recovered from an estimated $10,412 worth of cable stolen," Mr Ross said.

"Those amounts are solely scrap-metal values and are nowhere near the replacement cost faced by power companies to repair the damage."


WEL Networks asset management general manager Tas Scott said copper thefts put employees and members of the public at risk of electrocution.

The 17-year-old will appear in the Hamilton District Court on Tuesday.