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High Voltage - a summary

High Voltage (HV) systems are key for the transmission of the UK’s electricity, from generation to distribution through a complex network of overhead power lines and underground cables, transformers, switch gear and control equipment to safely deliver electricity for use in heavy industry, railway and commercial buildings such as shopping centres, large complexes, data centres, schools and hospitals – to name a few.

The National Grid own and operates the National Electricity Transmission Systems in England and Wales and operates the system in Scotland, transmitting voltages between 132 kilovolts (kV) to 400 kV.

The Distribution Network Operators (DNOs) own and operate the distribution network which brings electricity from the national transmission network to homes and businesses, these voltages typically range from 11 kV to 33 kV before finally stepping down to low voltage as  seen within small commercial and domestic premises.

Within this structure work can be carried out on the public HV networks by Independent Connections Provider (ICP) who will undertake work that will be adopted by the DNO to form part of their distribution systems – this is called contestable work.

Non contestable HV work is classed within the boundary of any site controlled and inspected by the DNO.

Private HV networks exist at the point where the responsibilities of the HV asset doesn’t form part of the public network and are governed by the client's own safety rules.