Electrical Safety on Site: Isolating, Testing and Avoiding the Most Common Mistakes

The Risk in Numbers

Electrical accidents cause approximately 30 deaths and over 1,000 serious injuries in UK workplaces each year. On construction sites, the main dangers are:

• Contact with overhead power lines
• Contact with underground cables
• Faulty portable equipment
• Working on or near live systems
• Inadequate isolation before maintenance

The Golden Rule: Safe Isolation

Before carrying out any work on an electrical system, the supply must be isolated and locked off. This means:

1. Identify the correct isolation point
2. Switch off and lock off (use a lockout device)
3. Attach a danger tag with your name and date
4. Prove dead using a voltage indicator (test on a known live source first, then on the circuit, then verify the tester works again)
5. Never rely on a colleague having isolated — verify yourself

This sequence is sometimes called Prove Dead and should be standard practice for all electrical work.

Overhead Lines

Contact with overhead power lines causes some of the most severe electrical incidents on construction sites. Before starting work:

• Contact the Distribution Network Operator (DNO) to establish if lines can be de-energised
• Erect goal posts (height restriction barriers) if vehicles or plant operate near lines
• Maintain minimum clearances — 6.2m for most overhead lines, 9.2m for high voltage

Underground Services

Before any digging:

• Obtain utility records (contact LSBUD or Dial Before You Dig)
• Use a cable avoidance tool (CAT) and genny to sweep the area
• Hand dig within 500mm of identified service locations
• Never assume drawings are accurate — always scan

Portable Appliance Testing (PAT)

All portable electrical equipment on site should be:

• Visually inspected before each use (damaged cables, plugs, casings)
• PAT tested at appropriate intervals — typically 3 months for construction environments
• Removed from service if defective — never 'make do'

Reduced Voltage Working

For most portable tools on construction sites, the standard is 110V centre-tapped to earth using a yellow transformer — not 230V. This limits the shock voltage to a maximum of 55V, significantly reducing the risk of fatal shock.

Site Safety UK generates electrical safety RAMS and method statements tailored to your specific task.