Regulations for the design, construction and inspection of high voltage electrical installations take into account the fact that each installation will be different, and are designed according to electrical engineering safety principles.


Anybody who designs or supervises the design of, high voltage installations must ensure that the finished design would be electrically safe when it has been constructed, installed, or manufactured.

Regulation 14 of the Electricity (Safety) Regulations 2010(external link), makes it an offence to complete a design – including supervision – which, if constructed, would not be electrically safe.

Owners of installations are responsible for ensuring the risks of injury to persons or damage to properties are minimised. This requirement applies to design, construction, and maintenance.

When designing high voltage installations, consideration must be given to a range of issues that are more significant than those for a low voltage installation. Such issues include the following:

  • Insulation levels to withstand the highest voltage and/or impulse withstand voltages.
  • Minimum clearances to live parts taking into account electrode configurations and impulse withstand voltages.
  • Minimum clearances under special conditions.
  • The application of varies devices connected to the system.
  • The methods of installation of equipment, cables and accessories.
  • General requirements of installations regarding choice of circuit arrangement, documentation, transport routes, lighting, operation safety and labelling.
  • Special requirements with respect to buildings.
  • Protection measures with respect to access.
  • Protection measures with respect to fire.
  • Provision of earthing such as the system operates under all conditions and ensures safety of human life where there is legitimate access. 


Overhead lines must be capable of withstanding, without damage, the likely static and dynamic loading; and must not become unsafe or dangerous to the public or to persons likely to work on them. If overhead line structures fail to meet these requirements they must be marked and repaired or replaced within 12 months (or 3 months if there is a risk of injury or damage to property) ( Regulation 41).

High voltage conductors of overhead electric lines must be protected by earth fault protection.

Installations protected by an earthing system compliant with ECP 35 or, in the case of a railway electrification system, IEC 62128–1 are deemed to prevent danger to any person.

The installation must be capable of being isolated from its supply of electricity. If the installation comprises separate parts, each part must have an isolation fitting to disconnect that part from its supply of electricity.

Visible and durable notices reading “Danger Live Wires” or equivalent warnings must be installed on all poles or supports carrying uninsulated conductors that may be climbed without the use of equipment.

The owner must keep records and plans of the installations.

Certification must be carried out on high voltage installations using a Certificate of Compliance.

The person certifying the inspection must retain the certificate and make it available when requested by the Regulator.

As per Regulation 62(external link), the following regulations must be taken into consideration during design and construction:

Regulation 34 – Protective fittings(external link)

Regulation 40 – Safety checks(external link)

Regulation 41 – Structural loading(external link)

Regulation 42 – Requirements for earthing systems(external link)

Regulation 43 – Isolation fittings(external link)

Regulation 44 – High voltage conductors of electric lines(external link)

Regulation 45 – Permanent notices(external link)

Regulation 46 – Keeping records and plans(external link)

Regulation 66 – Content of certificate of compliance(external link)

Inspection and connection

Electrical work on installations that operate at high voltages must be inspected.

This inspection and third-party verification must be carried out to ensure that the installation will be safe when connected to a supply and has been done in accordance with the Act and Regulations.

Inspections can only be carried out by a person who is authorised by their registration and practising licence to carry out inspection work and by a person who has not carried, supervised or certified that work.

Only when the installation has been confirmed to be compliant may the inspection certificate portion of the Certificate of Compliance be signed by the inspector.

The inspection of work done on a high voltage installation must verify that the installation complies with ECP 34 and also with Regulations 34, 41(1), 42(1), 43(1), and 44(1), as if references in those Regulations to works were references to high voltage installation.

Safety check

A person who owns or operates works, installations, fittings, or appliances must not use, and must not allow anyone to use, the works, installations, fittings, or appliances if they are electrically unsafe.

Before any high voltage installation work can be connected to a supply, the person intending to make the connection must do ALL of the following:

  • inspect and certify the work
  • be satisfied that tests have been carried out to ensure the electrical safety, the compatibility with the supply system, and the correct polarity, phase rotation and protection of the supply
  • verify the technical safety compliance of the supply

after the installation work has been permanently connected to a supply issue an Electrical Safety Certificate (ESC) for the connection.