Business Energy Glossary
What is voltage optimisation?
Voltage optimisation is the installation of equipment that reduces the incoming UK electricity supply voltage to a lower, more efficient operating level for site equipment. The standard UK supply voltage is 230 V single-phase or 400 V three-phase, but in practice the voltage delivered is often closer to the upper end of the permitted range (around 240 V to 250 V). Equipment runs more efficiently at the lower end of the range. Voltage optimisation typically reduces electricity consumption by 5 to 15 per cent on sites with high lighting and motor loads, with payback periods of 2 to 5 years.
Voltage optimisation has been a mainstream commercial energy efficiency measure since the 2000s. The benefit comes from the way most electrical equipment behaves at different voltages: lighting, heating, and many motors consume more power at higher voltages than necessary for normal operation. Reducing the supply voltage produces savings without affecting operations.
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Why voltage optimisation works
The UK grid is regulated to deliver supply voltages within +10/-6 per cent of nominal (230 V single-phase, 400 V three-phase). In practice, distribution networks deliver towards the upper end of the range to avoid undervoltage at the customer end of long cable runs. Many UK business sites receive supply voltages between 240 V and 250 V.
Equipment is rated to operate at nominal voltage or below. At higher voltages, most equipment consumes more power without performing more work:
- Resistive loads (heating, lighting). Power consumption rises with the square of voltage. A 10 per cent voltage increase produces 21 per cent more power consumption.
- Induction motors. Higher voltage produces higher magnetising current and increased losses, particularly under partial loading.
- Electronic equipment with switching power supplies. Generally consume the same power regardless of input voltage (so do not benefit from voltage reduction).
Reducing the supply voltage to the lower end of the permitted range reduces consumption without affecting equipment operation.
How a voltage optimiser works
A voltage optimiser is installed downstream of the supply meter, between the meter and the site distribution board. The equipment reduces the supply voltage by a defined amount, typically 8 to 20 V on a single-phase supply (or 15 to 35 V phase-to-phase on three-phase).
Two common technologies:
- Fixed-tap optimisers. Simple transformers with a fixed reduction ratio. Cheaper to install; cannot adapt to changing supply voltages.
- Variable-tap optimisers. Electronically controlled units that maintain a target output voltage regardless of supply voltage variation. More expensive but maintain savings consistently.
The optimiser is typically rated for the full site load and includes bypass switching for maintenance.
Typical savings
Savings depend on the equipment mix:
| Load type | Typical saving from 10 V reduction |
|---|---|
| Lighting (lamps, fluorescent) | 10 to 20% |
| Resistive heating | 10 to 20% |
| Induction motors (partial load) | 5 to 10% |
| Induction motors (full load) | 2 to 5% |
| Electronic loads with switching supplies | 0 to 2% |
| LED lighting | 0 to 5% |
Overall site savings of 5 to 15 per cent are typical, weighted by the load mix.
Cost and payback
Indicative 2024 installed costs:
- Small commercial (under 100 A single-phase): £2,500 to £6,000.
- Mid-commercial (100 A three-phase): £8,000 to £18,000.
- Larger industrial (400 A three-phase and above): £25,000 to £80,000.
Payback periods are typically 2 to 5 years depending on consumption and load mix. The equipment has an operating life of 20+ years with limited maintenance, making the long-term return attractive.
Where voltage optimisation suits
Voltage optimisation works best for sites with:
- High proportion of resistive lighting (traditional lamps, fluorescent), heating, and motor loads.
- Confirmed high incoming supply voltage (above 235 V single-phase, 410 V phase-to-phase).
- Stable consumption profile supporting consistent savings.
- Long-term occupation of the building (justifying multi-year payback).
Voltage optimisation works less well for sites with predominantly LED lighting, modern electronic equipment, or where the incoming voltage is already at the lower end of the range.
Installation considerations
Key factors:
- Site survey. A pre-installation survey measures the actual incoming voltage profile across at least a week to confirm the available headroom.
- Load compatibility. Some specialist equipment (medical, precision manufacturing) has voltage-specific requirements that voltage optimisation could affect.
- Power supply variation. Voltage optimisation reduces the buffer against short-term voltage drops. Sites with frequent voltage dips may need an undervoltage protection mechanism.
- Monitoring. Post-installation monitoring confirms actual savings against the pre-installation baseline. Most installers provide monitoring as part of the deal.
For larger installations, an independent energy consultant or supplier-side survey is often a good investment before committing to the equipment specification.
voltage optimisation FAQs
What is voltage optimisation?
The installation of equipment that reduces the incoming UK supply voltage to a lower, more efficient operating level for site equipment. Typically reduces electricity consumption by 5 to 15 per cent.
How does voltage optimisation save energy?
Most resistive loads (lighting, heating) and induction motors consume more power at higher voltages than necessary for operation. Reducing supply voltage to the lower end of the permitted range reduces consumption without affecting equipment function.
How much can voltage optimisation save?
Typically 5 to 15 per cent of total electricity consumption, weighted by load mix. Sites with high lighting and motor loads see higher savings; sites with mostly electronic equipment see less.
How much does voltage optimisation cost?
Indicative 2024 installed costs: £2,500 to £6,000 for small commercial single-phase, £8,000 to £18,000 for 100 A three-phase, £25,000 to £80,000 for larger industrial installations.
What is the payback for voltage optimisation?
Typically 2 to 5 years depending on site consumption, incoming voltage level, and load mix. The equipment has a 20+ year operating life, producing strong long-term returns.
Will voltage optimisation affect my equipment?
Generally no, provided the equipment is rated for the reduced voltage (which most UK commercial equipment is). Specialist equipment with voltage-specific requirements should be reviewed before installation.
Does voltage optimisation work with LED lighting?
Less effectively. LED lighting maintains consistent light output across the input voltage range, so voltage reduction produces smaller savings on LED. Voltage optimisation is more cost-effective on sites with traditional lighting.
Can I install voltage optimisation myself?
No. Voltage optimisation requires a qualified electrical installer because it involves work on the supply intake. Most suppliers offer installation as part of the package.