Voltage Optimisation

Use this page when you need to check whether voltage optimisation is suitable, estimate likely savings, or prove what voltage is present before and after a voltage reduction system is fitted.

Voltage optimisation is only useful when the site voltage is higher than the equipment needs and when the connected loads will benefit from voltage reduction. A logger gives the proof needed before committing to a voltage optimisation project.

The most useful measurements are the incoming voltage profile, the lowest and highest voltages seen over time, and, where possible, the current and power behaviour of the site before and after any change.

What to measure

Incoming voltage on one phase or all three phases over a representative period.
Highest and lowest voltage values with dates and times.
Voltage stability during working hours, off-peak periods and weekends.
Current, kW and energy before and after voltage optimisation where power measurement is needed.
Whether any low-voltage risk exists after a proposed reduction.

Recommended loggers

Logger	Best fit	Measures
EC-7VAR-RS Electrocorder EC-7VAR-RS Three Phase Voltage, Current & Power Factor Recorder	Use when voltage optimisation needs to be assessed alongside current, power factor, kW and energy.	Three-phase voltage, current, power and energy.
EC-3V Electrocorder EC-3V Three Phase Voltage Recorder	Best for three-phase voltage profile proof before and after voltage optimisation.	Three-phase voltage.
EC-2VA Electrocorder EC-2VA Power Logger and Energy Recorder	Use for single-phase voltage, current, power and energy before-and-after checks.	Single-phase voltage, current, power and energy.
EC-2V Electrocorder EC-2V Voltage Logger	Best where a single-phase voltage logger with local display and setup flexibility is preferred.	Single-phase voltage.
EC-1V Electrocorder EC-1V (Mailable) Voltage Recorder	Best for a compact single-phase voltage check, including mailable investigations.	Single-phase voltage.

Detailed guidance

What voltage optimisation is trying to do

Voltage optimisation is used where the incoming supply voltage is higher than the ideal operating voltage for the equipment on site. In simple terms, some loads consume more energy when operated at a higher voltage than they need. For example, a 230V linear appliance used on a 240V supply will take about 4.3% more current and almost 9% more electricity than it would at 230V.

Sites fitted with a voltage optimisation system may achieve reductions in energy consumption, cost and carbon emissions, but the result depends strongly on the equipment connected to the supply. The first step is therefore to measure the existing voltage profile and understand what types of load are present before assuming that savings will be available.

Why logging matters before voltage optimisation

A spot voltage reading is not enough. Supply voltage changes through the day and week, often rising during off-peak periods and falling during heavier loading. A logger shows the normal profile, the highest and lowest values, and whether there is enough headroom to reduce voltage without creating a low-voltage risk.

For a voltage-only assessment, use a voltage logger such as the EC-3V, EC-2V or EC-1V. Where the savings case also needs current, kW, power factor or energy proof, use a power logger such as the EC-7VAR-RS or EC-2VA.

Effects on different electrical loads

A common misconception is that reducing voltage always causes current to rise so that power remains unchanged. That is true for some fixed-power loads, but not for every load on a real site. Most commercial and industrial sites have a mixture of loads, and any savings from voltage optimisation are the aggregate result across that mixture.

Three-phase AC motors

Three-phase induction motors are common in refrigeration, pumps, compressors, fans, air conditioning, conveyors and lifting systems. Excess voltage can cause flux saturation in the motor iron core, wasting energy through eddy currents and hysteresis losses. Excess current also increases copper losses and heat, and long-term overvoltage can reduce motor life.

If overvoltage is high enough to cause saturation, reducing voltage can reduce waste. However, motors designed for nominal supply voltage, such as 400V phase-to-phase or 230V phase-to-neutral, should cope with normal supply variation within limits of roughly +/-10%. If they are not operating in saturation, savings may be small.

Reducing voltage to an induction motor can slightly affect speed because slip increases, but speed is mainly determined by supply frequency and the number of motor poles. Motor efficiency is usually best at a reasonable load, often around 75%, and near the designed voltage. Very lightly loaded motors, especially around 25% load, and smaller motors tend to benefit most from voltage reduction.

Motors driven by variable speed drives normally use the same power as before, but may draw more current. With less stored energy in their DC bus capacitors, they may also be more vulnerable to power dips.

Switched mode power supplies

Switched mode power supplies generally use the same power after voltage reduction, drawing slightly more current to do so. This can slightly increase cable losses and, in some circumstances, may increase the risk of an MCB tripping where a circuit is already close to its limit.

Lighting

Lighting can be important because it may be in use for long periods. Incandescent lighting will draw much less power when voltage is reduced, but light output will also fall and lamp life may increase. Fluorescent and discharge lighting with conventional magnetic ballasts can also show reduced power consumption, although light output may reduce as well.

Fluorescent lamps on modern electronic ballasts generally use approximately the same power and provide the same light output. To maintain the same wattage at a reduced voltage, they draw more current, which can increase cable losses. Some lighting controllers and ballasts can generate harmonic distortion, and some voltage optimisation equipment may help filter certain power-quality problems.

A common concern is that lighting may fail to strike at lower voltage. Voltage optimisation should not simply reduce voltage as far as possible; the aim is to bring the supply closer to the voltage at which the equipment was designed to operate.

Heating loads

Simple heaters consume less power when voltage is reduced, but they also give out less heat. Thermostatically controlled space or water heaters may run for longer to produce the required heat output, so the overall saving may be little or none.

Energy and emissions savings

The savings from voltage optimisation come from the combined response of all equipment on the site. Older lighting, discharge lighting and equipment with conventional control gear often provide better saving potential than modern buildings dominated by electronic power supplies, variable speed drives and high-efficiency motors.

Research in Taiwan suggested that, for an industrial supply with voltage reduction upstream of the transformer, energy consumption fell by about 0.241% for each 1% voltage decrease, and rose by about 0.297% for each 1% voltage increase. That result assumed a particular mixture of loads, including fluorescent lighting, incandescent lighting, air conditioning, single-phase motors, small three-phase motors and large three-phase motors. A modern northern European site may have less saving opportunity because it is likely to have less incandescent lighting, more electronic lighting, more variable speed drives and higher motor efficiencies.

Be realistic about the savings case

Voltage optimisation can save energy, but the purchaser needs to determine the likely saving in their own environment. The load mix matters. For example, a plastic extrusion company was reportedly told it could save 20% of its total electricity bill with voltage optimisation. The claim ignored that about 85% of the electricity was used to heat extruder heads, where the process required a fixed temperature. The possible saving was therefore only on the remaining 15% of use, making the real saving closer to 4%.

This is why logging is important. Measure the voltage profile, understand the connected loads, and, where possible, record before-and-after data so the result is proven rather than assumed.

How to approach the investigation

Record the existing voltage profile before any voltage optimisation equipment is specified.
Check both high-voltage periods and low-voltage periods, not just the average voltage.
If savings need to be proven, record comparable before-and-after load periods.
Consider whether sensitive equipment, motors, controls or seasonal load changes affect the decision.

Related guides and products

These pages and products give the next level of detail for this application.

Application guides:

Voltage Problem Loggers: for high voltage, low voltage, voltage variation, dips and interruptions.
Energy Audit Loggers: for energy audits, load profiles, peak demand and before/after savings proof.
All application guides: choose an Electrocorder by the job or problem you need to investigate.

Relevant products:

EC-7VAR-RS: Electrocorder EC-7VAR-RS Three Phase Voltage, Current & Power Factor Recorder.
EC-3V: Electrocorder EC-3V Three Phase Voltage Recorder.
EC-2VA: Electrocorder EC-2VA Power Logger and Energy Recorder.
EC-2V: Electrocorder EC-2V Voltage Logger.
EC-1V: Electrocorder EC-1V (Mailable) Voltage Recorder.