Construction sites in the UK use 110-volt reduced low voltage supply systems to limit the severity of electric shock from portable tools. The 110V system uses a centre-tapped earth referenced transformer, meaning the maximum voltage to earth is only 55 volts. Residual current devices provide additional protection on 230-volt circuits by detecting earth leakage and disconnecting the supply within milliseconds. Understanding how these systems protect you, and the importance of not bypassing them, is essential for every site worker.
Key Hazards
Electric shock from 230-volt equipment used without RCD protection on site
110-volt system protection defeated by damaged cables or modified connections
RCD protection bypassed or not tested allowing dangerous faults to persist
Electric shock in wet conditions where even 110 volts can cause serious injury
Control Measures
Use 110-volt tools as the standard for all portable equipment on construction sites.
Ensure all 230-volt supplies are protected by a 30mA residual current device.
Test RCDs using the integral test button at the start of every shift before connecting equipment.
Inspect all 110-volt cables, plugs, and connectors before use for damage and correct assembly.
Never use domestic 230-volt extension leads or plug adaptors on a construction site.
Replace any damaged cable, connector, or transformer immediately and do not attempt to repair.
Ensure 110-volt transformers are positioned in dry locations and protected from mechanical damage.
Do not bypass or modify any electrical protection device under any circumstances.
Report any electric shock, tingle, or unusual sensation from equipment to your supervisor immediately.
Remember
110-volt systems reduce the maximum shock voltage to 55 volts which is significantly safer than 230 volts.
230-volt equipment on site must always be protected by a 30mA RCD as an absolute minimum.
Test the RCD using the test button every day — an untested RCD may not protect you when needed.
Damaged 110-volt cables and connectors must be replaced, not taped up or repaired on site.
In wet conditions even 110 volts can cause serious harm, so inspect equipment more carefully.
Never bypass, bridge, or modify any electrical safety device — doing so is illegal and potentially fatal.
Applicable Legislation: Electricity at Work Regulations 1989 · BS 7671 (IET Wiring Regulations) · HSG141 (Electrical Safety on Construction Sites) · Health and Safety at Work etc. Act 1974