9.1 Electrical Safety on Construction Sites: Temporary Supply, RCDs, Competent Persons and Safe Isolation

How electricity harms

Risk rises with wet conditions (Malaysian rain, concrete work, dewatering), damaged insulation, steel structures and confined conductive spaces, and long cable runs across traffic routes.

The law

• OSHA 1994 section 15(2)(a): safe plant and systems of work.
• CDM 2024 regulation 27:
  • (1) energy distribution installations must be suitably located, checked regularly and clearly marked where necessary to prevent danger
  • (2) and (3) overhead power cables must be diverted, isolated and earthed, or protected with warning notices, barriers and suspended protection
  • (4) no work that could create risk from underground services unless suitable measures are taken
  • most breaches carry up to RM500,000 or one year or both
• Electricity Supply Act 1990 (Act 447) and Electricity Regulations 1994, administered by the Energy Commission (Suruhanjaya Tenaga):
  • electrical work must be done by persons holding the appropriate certificate of competency: wireman, chargeman, electrical supervisor, competent electrical engineer or cable jointer
  • installations must be done by registered electrical contractors
  • installations must be tested and certified before connection to supply
• Regulation 36 of the Electricity Regulations 1994, protection against earth leakage by residual current devices (RCDs):

On construction sites, hand tools are everywhere, so every final circuit feeding socket outlets for portable tools needs 30 mA RCD protection. The international standard for construction-site installations, IEC 60364-7-704, takes the same approach.

Temporary site distribution

A typical arrangement runs from the utility supply or a generator to a main board, then sub-distribution boards, then socket-outlet boards near the work.

What the SSS inspects

Only competent persons (Energy Commission certificates) may install, alter or repair the installation. Workers must never "borrow" power by opening boards.

Portable tools and equipment

• Inspect before use: user checks for damaged casings, cables and plugs. Withdraw defective tools at once and tag them "DO NOT USE".
• Inspect and test periodically: by a competent person, with a site tag or register showing the next due date.
• Choose safer supplies: battery tools or reduced-voltage systems (such as 110 V centre-tapped earth transformers) where practicable, especially in wet or confined areas. Double-insulated tools reduce shock risk.
• Never use domestic extension reels on site, and never use tools with missing earth pins.

Working near cables

• Overhead lines: CDM regulation 27 and Section 3.1. Check the line owner's safe distance, set goalposts and barriers at crossings, and plan crane, pump and tipper positions so they cannot reach the line.
• Underground cables: use drawings, cable locator scans and hand-dug trial holes (Section 6.4). DOSH's excavation bulletin also says workers using hand tools where the exact cable location is unknown should wear insulated gloves and footwear.

Safe isolation and work on electrical systems

Work on or near electrical equipment should be done dead wherever possible:

1. Identify the circuit and equipment from drawings and labels.
2. Isolate at the correct point. Switching off a final circuit breaker is not enough if other supplies feed the equipment.
3. Lock off with a personal lock and tag each isolation point. Use an electrical permit for complex systems.
4. Prove dead with an approved voltage indicator, which is itself checked on a known live source before and after use.
5. Earth where required, for example on high-voltage systems, by an authorised person.
6. Re-energise only after all workers are clear, all locks removed by their owners, and the work checked.

Live work should be avoided. Where it is unavoidable, it must be done only by competent persons following a specific procedure, with insulated tools, PPE and a second person present.

Responding to electric shock

1. Do not touch the casualty until the supply is switched off or the casualty is separated using non-conductive means. For high-voltage lines, keep well clear and call the line owner.
2. Call for help (999) and start CPR if the casualty is not breathing normally. Use an automated external defibrillator (AED) if one is available.
3. Treat burns, and send every shock casualty for medical assessment, because internal injuries and heart rhythm problems can be delayed.
4. Report and investigate. A shock causing serious injury, or an electrical fire with a long plant stoppage (NADOPOD Second Schedule item 3), may need notification to DOSH.

Scenario: the wet basement

During rain, workers in a flooded basement are using a pump and a grinder plugged into a board with its door off, through a taped joint lying in water. The RCD test record has not been updated for two months. The SSS:

1. Stops work, clears the area and has the board isolated by the site chargeman.
2. Has the damaged cable replaced, the joint removed, and the cable routed off the floor on hooks.
3. Has the RCDs tested and shown to trip within their rated current, confirms the 30 mA protection on the tool circuits as Regulation 36(3) requires, and refits the board door with a lock.
4. Swaps the grinder for a battery tool. The pump supply is reviewed by the electrical engineer.
5. Adds weekly RCD test-button checks to the site inspection checklist.