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Site Transformers: How to Ensure Power Safety on UK Construction Sites
Site transformers reduce hazardous mains voltage to a safer 110V centre-tapped-to-earth supply, protecting workers who use tools, extension leads and portable lighting in demanding construction environments. This low-voltage system is essential for reducing electric shock risks and keeping equipment stable on busy sites.
What Is a 110V Centre-Tapped-to-Earth Site Transformer?
A 110V centre-tapped-to-earth transformer divides the output into two 55V lines, each referenced to earth. If a worker touches one conductor accidentally, they are exposed to just 55V rather than the full 230V mains, significantly lowering injury risk.
How Site Transformers Protect Workers
- They isolate equipment from the 230V mains to reduce shock hazards.
- They deliver a controlled 110V output suitable for harsh site conditions.
- They limit potential shock voltage to 55V in the event of accidental contact.
- They protect extension leads and portable lighting commonly exposed to water and impact.
- They regulate load to prevent overheating, fire risk or tool damage.
Why 110V Is the Standard on UK Construction Sites
- The Health and Safety Executive (HSE) recommends reduced low-voltage systems for portable tools.
- The centre-tapped system safely limits shock severity during cable damage.
- 110V is ideal for equipment used outdoors, in wet areas or on uneven terrain.
- Most site power tools are manufactured specifically for 110V compatibility.
Common Equipment Powered by Site Transformers
- Corded power tools
- Portable and task lighting
- Temporary lighting strings
- Heavy-duty extension leads
- Pumps, fans and small machinery
How 110V Site Transformers Improve Safety
| Safety Feature | What It Does | Worker Benefit |
| 110V reduced voltage | Lowers 230V to 110V | Less severe electric shocks |
| Centre-tapped-to-earth | Splits supply into two 55V lines | Limits exposure in contact incidents |
| Full electrical isolation | Prevents faults travelling from mains | Reduces system-wide hazards |
| IP-rated casing | Guards against dust, mud and moisture | Safer for outdoor and wet locations |
| Overload protection | Stops circuits during excess load | Prevents overheating and fire risks |
Real-World Problem and Solution
Problem:
A site was running 230V tools through long extension leads, causing frequent tripping, overheating and mild shocks in damp areas.
Solution:
Switching to 110V centre-tapped-to-earth site transformers eliminated overheating, improved safety for portable lighting and kept all equipment compliant with HSE recommendations. Workers reported immediate improvements in reliability and safety.
If you’re planning your next project, you may also find it helpful to read our guide on how to choose the right 110V site transformer for your construction site, which builds naturally on the safety principles discussed here.
FAQs
What size site transformer do I need?
Add the total wattage of all tools you will run at the same time, then divide by 110V to find the required amperage. For example, tools totalling 4000W need around 36A, so a 5kVA transformer provides safe capacity.
How often should site transformers be tested?
Construction-site transformers should receive PAT testing every 3 months, with visual checks before each use and a formal annual inspection by a qualified electrician.
Can site transformers be used with generators?
Yes, as long as the generator’s output exceeds the transformer rating by at least 25% and provides stable, well-earthed power.
What happens if a site transformer is overloaded?
The thermal protection should disconnect power automatically. Consistent overloading can cause overheating and insulation damage, so always stay within the rated capacity.
Do site transformers work in freezing conditions?
High-quality units operate safely between -20°C and +40°C. Choose outdoor-rated models with proper IP protection to prevent moisture or condensation issues.