High Voltage (HV) Safety

High voltage (HV) is defined as above 1,000V AC or 1,500V DC in the UK under the regulations.
HV systems include 11kV and 33kV cables, transformers, switchgear, and overhead lines on construction sites.
Contact with HV equipment causes fatal electrocution — the energy levels prevent any chance of survival.
HV arcing can jump gaps of several centimetres through air, killing without direct physical contact.
Only HV Authorised Persons may switch, isolate, or permit work on high voltage equipment.
Safe approach distances must be maintained — a minimum of 3 metres from 11kV equipment.
The Electricity at Work Regulations 1989 and HSE guidance note GS6 apply to all HV work.
HV cables may be buried alongside LV cables and other services — they look similar until damaged.
Substation construction involves working near energised HV equipment during commissioning phases.
Emergency procedures for HV incidents differ from LV — do not approach the casualty until confirmed safe.

Fatal contact	HV electrocution is almost always fatal — there is no safe contact with HV systems.
Arc flash	HV arcing produces explosive energy releases causing severe burns at distance.
Approach distance	Getting too close to HV without authority or isolation can kill without contact.
Legal compliance	Only HV Authorised Persons may work on or near HV equipment under strict regulations.

Do

Don't

Maintain the minimum safe approach distance from all HV equipment at all times.
Confirm that only HV Authorised Persons carry out switching and isolation operations.
Follow the HV safety rules and permit system without deviation.
Display warning signs and barriers around all HV equipment and compounds.
Report any damage to HV cables, switchgear, or transformer enclosures immediately.
Ensure HV isolation is proved dead with an approved HV voltage indicator.
Apply HV earths after isolation before any work on HV equipment begins.
Brief all site workers on the location of HV equipment and approach distances.
Follow the specific emergency procedure for HV incidents — do not touch the casualty.
Treat all cables as HV until confirmed otherwise by a competent person.

DON'T approach within the safe distance of any HV equipment unless authorised.
DON'T open HV switchgear, transformer doors, or enclosures without HV authority.
DON'T touch or attempt to rescue a casualty in contact with HV equipment.
DON'T excavate near HV cables without specific HV safety precautions in place.
DON'T store materials or park plant against HV compounds or substations.
DON'T work on HV systems without confirmed isolation, proving dead, and earthing.
DON'T climb HV structures, poles, or pylons without specific authorisation.
DON'T assume a cable is LV because it looks small — HV cables can be slim.
DON'T bypass HV safety rules to save time — the consequences are fatal.
DON'T carry long or tall items near HV overhead lines without a clearance check.

See also: Electrical Safety Awareness | Arc Flash Awareness

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