They struck twice to take the metal from an electricity substation at Fishcross, Alloa.
Guy Jefferson, operations director at ScottishPower Energy Networks, said: "These events are deeply concerning. The criminals responsible are leaving substations badly damaged and unsecured - exposing residents to potentially very dangerous situations.
"It is only by sheer luck the criminals have not been badly injured or even killed. One wrong move in the vicinity of 11,000 volts of electricity will result in horrific injuries.
"It is incredible anyone would risk life and limb for the sake of stealing small amounts of scrap metal that will have a minimal sell-on value."
Chief Inspector Stephen Sneddon, of British Transport Police, said: "Just by being in the substation is putting themselves at risk."
The Scottish Government is preparing to announce new safeguards to help tackle the increase in scrap metal thefts.
However, South of Scotland Labour MSP Graeme Pearson, who was a policeman for nearly 40 years and a former director general of the Scottish Crime and Drug Enforcement Agency, said he had been pushing for 18 months to have rules tightened, during which time metals thefts continued to increase.
Network Rail has also called for greater checks on scrap metal industry and monitoring of transactions.
Earlier in the summer trains were cancelled on part of the Aberdeen-Inverness route after thieves took 1¼miles of electrified copper signalling cable in separate incidents.
The Scottish Government said it was considering cashless transactions-only for scrap, which Mr Pearson said would make the scrap metal trail more transparent.
He said introducing bank credit payments only for scrap metal would ensure confidence in the industry.
However, he added: "The Scottish Government has prevaricated on this issue for 18 months.
"As a result we continue to have cable and metals being stolen all over the country, disrupting commuters, telephone connections and internet links, thereby costing people, businesses and commerce significant financial losses and disruption at a time the economy is struggling to survive.
"Beer kegs, Calor Gas canisters, copper connectors for BT and many other connections are prime targets, with evidence of main resetters shipping the metals out of the country to be refined by smelter."
Mr Pearson said Lord Advocate Frank Mulholland told him earlier: "I agree with the member that preventing access to ready cash is a worthy aim."
A two-week police crackdown called Operation Caraway has just been launched. Officers from all 14 divisions of Police Scotland and the British Transport Police will target thieves and dealers who trade in stolen material.
Copper fetches about £4600 per tonne and thefts of track and signalling cable have cancelled 253 trains and cost Network Rail in Scotland almost £600,000 in the last three years.
A Scottish Government spokeswoman said it was "determined to tackle the increase in metal theft during recent years" and had launched a consultation in April.
She added: "It (the consultation) specifically focused on what conditions dealers should be subject to under a new licensing regime with all dealers licensed and looked at cash payments for metal. We are analysing the responses and will announce a way forward in the autumn.
"Tougher legislation needs to be combined with effective enforcement, which is why the British Transport Police have a specific team dedicated to tackling metal theft and the Crown Office and Procurator Fiscal Service has adopted a tougher prosecution policy in relation to this issue and courts now reflect the full consequential costs from an offence."