Live Equipment and Cables on Construction Sites

Construction sites often contain live electrical equipment and cables that remain energised during the works.
This includes existing building supplies, temporary site distribution boards, street lighting, and utility services.
The Electricity at Work Regulations 1989 require that no live work is carried out unless absolutely unavoidable.
Refurbishment and fit-out projects frequently involve working alongside live mains supplies at 230V or 415V.
Wastewater treatment works and process sites may have live MCC panels and HV switchgear during construction.
Cable strikes during excavation remain one of the most common causes of electrical injury on UK sites.
Temporary 110V site supplies use centre-tapped transformers limiting shock voltage to 55V — but are not risk-free.
Live cables may be concealed behind walls, under floors, in ceiling voids, or buried in the ground unmarked.
HSE Guidance Note GS6 recommends a safe system of work including isolation, proving dead, and locking off.
Only authorised and competent persons may work on or near live electrical equipment or carry out isolations.

Prevent electrocution	Contact with live conductors kills construction workers every year — 230V mains supply is fatal in most circumstances.
Arc flash danger	Accidental short circuits on live equipment cause arc flash — temperatures reach 20,000°C causing severe burns and blast injuries.
Legal prohibition	The Electricity at Work Regulations 1989 prohibit live working unless there is no reasonably practicable alternative.

Do

Don't

Treat all cables as live until proven dead by a competent person using approved test equipment.
Check drawings and service records before any work that could disturb existing cables.
Use a CAT and Genny scan before any penetration of walls, floors, ceilings, or ground.
Ensure isolations are carried out, locked off, and proved dead before work begins.
Mark all live cables and equipment with warning signs and barriers visible to all trades.
Route temporary cables on cable stands clear of walkways, traffic routes, and water.
Report any damaged cable, exposed conductor, or burning smell to the supervisor immediately.
Confirm the site electrical authorisation system and who is permitted to carry out isolations.
Use insulated tools rated for the voltage when working near energised equipment.
Brief all workers on the location of live equipment and exclusion zones before starting tasks.

DON'T assume a cable is dead because the lights are off or the circuit appears unused.
DON'T drill, nail, cut, or fix into any surface without first scanning for concealed cables.
DON'T remove warning signs, barriers, or covers from live electrical equipment or panels.
DON'T carry out any electrical isolation unless you are the designated authorised person.
DON'T run temporary cables through water, across sharp edges, or under heavy traffic routes.
DON'T store materials, scaffolding, or waste against or on top of electrical distribution boards.
DON'T open electrical panel doors or enclosures unless you are competent and authorised to do so.
DON'T use metallic tools, tape measures, or ladders near exposed live conductors or busbars.
DON'T bypass, bridge, or defeat any electrical safety device, RCD, or circuit breaker.
DON'T enter any electrical exclusion zone without written authorisation and correct PPE.

See also: Electrical Safety Awareness | Isolation and Safe Systems of Work

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