THE cause of a power cut that blacked out more than 200,000 properties across the north remained a mystery last night.
Street lights went out, train services were disrupted and shops and bars were forced to close early as they were plunged into darkness.
Vital radio services monitoring the shipping distress channel were also knocked out and mobile phone masts stopped transmitting.
First Minister Alex Salmond even held an emergency meeting of the Scottish Government’s resilience committee by candlelight.
Helicopter and foot patrols failed yesterday to pinpoint the cause of the problem that caused the “highly unusual” mass outage.
A single fault on a 55-mile high-voltage line between the new Knocknagael substation near Inverness and Blackhillock in Moray is suspected of causing the power failure.
But by last night, engineers had been unable to identify the exact location.
Scottish Hydro Electric Power Distribution said the massive outage could have been caused by a lightning strike or debris hitting an overhead line.
The power cut happened shortly after 8.30pm on Wednesday and, at its peak, affected about 205,000 homes from Fort William to Orkney and Moray to the Western Isles.
Radio services for the shipping distress channel were knocked out in Orkney and the Far North coast, prompting coastguards to have staff ready to mount vigils on high ground with hand-held radios to listen for stricken vessels.
The Channel 16 VHF radio equipment at Wideford, Orkney, and Dunnet Head at Thurso failed at about 9.30pm.
One site has no back-up generator, while the other did not work, and a Coastguard spokeswoman said there was a risk of officers missing distress calls.
She said those on watch would have struggled to raise the alarm as the power cut had caused widespread disruption of mobile phone coverage.
The emergency services said they received several calls relating to alarms set off by the outage but added that there were “no significant issues”.
NHS Highland said the emergency generators at hospitals kicked in automatically and there was no disruption to services or patients.
Mr Salmond chaired a candlelit meeting of the Scottish Government resilience committee at the Cabarfeidh Hotel in Stornoway following the power failure.
The Highlands and Islands Local Resilience Partnership also met to ensure contingency plans were in place if the power was out for a significant length of time.
Questions were asked yesterday about why a fault on one relatively small section could knock out the entire north network.
A spokesman for Scottish Hydro Electric Power Distribution said last night: “In terms of the scale of the interruption to supplies, this would have been caused by safety equipment acting as a circuit-breaker to safeguard the network.
“Our investigation into the cause of this highly unusual fault is ongoing.
“We are pleased that the majority of customers were back on within half an hour and everybody was back on within three hours.”
He apologised to affected customers and said the network was 99.9% reliable and the distributor was working with the National Grid to ensure the massive outage did not happen again.