Temporary Electrical Installations

Temporary electrical installations provide power to construction sites and must be designed and installed by competent electricians.
BS 7671 wiring regulations and BS 7375 code of practice for temporary electrical installations apply to all site supplies.
The preferred supply voltage on UK construction sites is 110 volts through a centre-tapped earth transformer.
Residual current devices providing 30mA protection must be installed on all 230 volt circuits used on construction sites.
Temporary distribution boards must be weatherproof, securely mounted, and protected from mechanical damage.
Extension leads and trailing cables must be inspected regularly — damaged cables are the most common cause of electrical fire.
Portable appliance testing at the correct frequency ensures hand tools and portable equipment remain safe for use.
Overloading circuits by daisy-chaining extension leads or using adaptors causes overheating and fires.
Temporary lighting installations must provide adequate illumination without creating trip hazards from trailing cables.
All temporary electrical installations must be inspected and tested before use and at regular intervals during the project.

Prevent electrocution	Poorly installed temporary supplies cause electric shock and electrocution — competent installation and 110 volt use protect workers.
Prevent fire	Overloaded circuits, damaged cables, and poor connections cause electrical fires on construction sites every week.
Legal requirement	BS 7671 and the Electricity at Work Regulations 1989 require safe temporary installations inspected at prescribed intervals.

Do

Don't

Ensure temporary electrical installations are designed and installed by competent electricians.
Use 110 volt supply through a CTE transformer for all portable tools on site.
Install 30mA RCD protection on all 230 volt circuits and test daily before use.
Inspect extension leads and trailing cables visually before each use.
Report any damaged cables, cracked plugs, or scorched connections immediately.
Keep distribution boards weatherproof, locked, and protected from plant damage.
Follow PAT testing schedules and check labels are current before using equipment.
Avoid daisy-chaining extension leads — use a single lead direct from the supply.
Route temporary lighting cables safely to prevent trip hazards in work areas.
Arrange formal inspection and testing of the temporary installation at required intervals.

DON'T install or modify temporary electrical supplies unless you are a qualified electrician.
DON'T use 230 volt portable tools on site when 110 volt alternatives are available.
DON'T use circuits without RCD protection — test the RCD daily before starting work.
DON'T use equipment with damaged leads, cracked plugs, or exposed wiring.
DON'T attempt to repair damaged cables yourself — report and replace them.
DON'T leave distribution boards open, unprotected, or exposed to rain.
DON'T use equipment with expired or missing PAT test labels.
DON'T daisy-chain extension leads or use multi-way adaptors on site.
DON'T trail temporary lighting cables across walkways without cable protection.
DON'T skip the formal inspection schedule for the temporary electrical installation.

See also: Electrical Safety Awareness | Portable Appliance Testing (PAT)

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