Dr David Sweeting, who has been an expert witness in many of the biggest bushfire cases during the past 20 years, said that in his experience clashing conductors were the major cause of bushfires.

He said the Rapid Earth Fault Current Limiter (REFCL) system would not stop fires sparked by clashing conductors.

The Terang/Cobden fire on St Patrick's Day was sparked by clashing conductors.

The state government was to spend $150 million to implement the new REFCL system but the costs and timetables for implementation have blown out.

The cost of REFCL is now about $700 million with industry experts tipping the blowout will exceed $1 billion.

Three weeks ago Victorian Energy Minister Lily D'Ambrosio told a budget estimates hearing that the REFCL would have prevented five fires on Black Saturday.

She is required to provide information backing up the claim to Member for Polwarth Richard Riordan later this week.

Dr Sweeting said he had been involved in investigating the cause of three fires on Black Saturday and REFCL may have stopped one of them.

"I don't think REFCL would have stopped any of them. It is possible it could have stopped one of them involving a concrete pole," he said.

"I suspect they can make the system work in the future but it's probably going to be too slow.

"There has to be an earth fault before it kicks in. Clashing conductors are the cause I found the most and that's the one REFCL can't respond to.

"It's not going to stop the main cause I've found when I've investigated bushfires."

Dr Sweeting investigated the Kilmore East, Beechworth, Pomborneit, Mickleham and Warrego bushfires.

He said high winds during extreme bushfire danger periods led to conductors clashing and then tinder dry vegetation igniting.

"I have found that conductors clashing is the major cause of the bushfires I have investigated and REFCL will do nothing to stop those fires," he said.

"I suspect the REFCL system is not worth what is being spent on it, especially if the cost is going to blow out from $150 million to now far more than that.

"I haven't done an economic study. You would also need to look at faults and the number of fire starts.

"Historically clashing conductors all happen in the air, not on the ground."

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Dr Sweeting has worked as an expert witness for both prosecutors and defendants and said he was happy to provide an opinion on REFCL because he was no longer dependent on being employed.

Vegetation falling on to power lines caused the St Patrick's Day fires at Camperdown/Gnotuk and Gazette/Hawkesdale, while a rotten power pole snapped sparking The Sisters/Garvoc blaze.

Leading REFCL expert Dr Tony Marxsen has previously refused to comment on the system when contacted by The Standard.

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