"There was a fault in the overhead network caused by the contacts at the top of the pole coming loose and crashing against each other, " she said.

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If spectrum is priced efficiently in an increasingly dynamic wireless world, the necessary overhead in network management and metering is likely to be quite costly.

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The system consists of sensors fitted on cables throughout the network, both overhead and underground, measuring current and conductor temperature.

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Network Rail is replacing overhead power lines installed 30 years ago, reducing the number of delays and cancellations caused by faults.

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Hybrids use diesel power where there were no overhead electric cables so could be used across the network without having to change locomotives or crews.

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Staff costs at Emirates are around 15% of overhead, against well over twice that for a typical American or European network carrier, says Mr Flanagan.

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Among the proposals are a new overhead connection across Anglesey and the Menai Strait, maximising use of existing network on the mainland, and replacing three underground cables in the Glaslyn estuary with 12.

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