Here are the most frequently asked questions we receive about the Powerstar voltage optimisation systems, from basic introductory questions such as what is voltage optimisation?  through to more specific questions such as ‘Where can I expect to see the best savings?’. The frequently asked questions section is updated regularly with new questions we are asked, if you don’t see the answer to your question here then please submit an FAQ through the form below and we will respond directly with an answer:

What is voltage optimization?

Voltage optimization is an electrical energy saving technique which is installed in series with the mains electricity supply to give an optimum supply voltage for the site’s equipment.

Voltage optimization improves power quality by balancing phase voltages and filtering harmonics and transients from the supply. Significant monetary and carbon savings can be achieved through voltage optimization.

How does voltage optimization work

What makes Powerstar unique?

The Powerstar voltage optimization system is a uniquely designed and patented triple-wound transformer with an efficiency of 99.91%.

By accurately controlling the incoming voltage it ensures that energy savings are maximised without compromising the supply.

The Powerstar patented basic schematic is overviewed below:-

1. Star Configuration (optional extra) – To eliminate harmonics. The two windings for each phase (outer and inner windings) are wound on the same core but in opposite directions. The windings are connected in a zig-zag fashion. For instance, the primary winding of Brown phase may be connected to the secondary of Black phase; the primary of Black phase would be connected to the secondary of Grey phase.

2. Delta Configuration – To further suppress any remaining harmonics.

3. Star Configuration – To control voltage.

Is Powerstar an electronic/intelligent system?
There are three variations in the Powerstar range.

The ‘original’ Powerstar offers fixed voltage optimization, ideal for those with stable (yet high) incoming voltage.

Powerstar MAX offers electronic-dynamic variable voltage optimization, for those with fluctuating voltage or varying loads.

Powerstar HV MAX offers HV side optimization with the addition of an amorphous core low loss transformer. Powerstar HV MAX is ideal for companies with their own HV supply.

What is an optimum voltage?

Optimum voltage is site specific. Each business has varying equipment, which in turn has varying voltage needs.

The national grid provides voltage at an average 493V. Some businesses may receive less than 493V, some may receive more.

The majority of electrical equipment is designed to run at 460V nominal.
In the majority of cases, businesses are being supplied voltage considerably higher than required.
A full site survey from the EMSc (UK) Ltd Powerstar team would uncover a businesses optimum voltage.

Does it really matter that my voltage is high?

Receiving voltage higher than needed into a site has no associated benefits.
In fact, the higher the voltage, the higher the energy consumption, hence higher electricity costs and higher carbon emissions.

Electrical appliances are also affected from unnecessarily high voltage. Higher voltage equals increased heat generation and reduced life expectancy.

Why doesn’t the national grid lower the voltage?

The national grid is obliged to transmit voltage in a way which ensures that all buildings (regardless of their proximity) receive between 440V and 515V depending on local conditions.
This means that the national grid has to withdraw voltage at a higher level than necessary to ensure that buildings furthest away from the substation receive a voltage within this specification.

Voltage drops with proximity so businesses closer to their local substation will receive a higher voltage than those at the furthest point.

What if voltage levels need to be adjusted after installation of Powerstar?

Powerstar has five tapings, 2.5V between. It is a very simple procedure to adjust (off-line) should a change be required. A visit from an engineer will be arranged, free of charge, to carry this out and train site electricians.

How do you know which Powerstar unit is best for your site?

Each of the Powerstar units are catered to suit varying sites, dependant on electrical appliances utilised.

In some circumstances it is easy to detect which voltage optimization unit may be most appropriate for a site (if you have your own HV transformer for instance) then Powerstar HV MAX would be the ideal solution.

In all circumstances a full site survey from a Powerstar consultant will uncover which Powerstar variation is most suited. Site surveys are completely free of charge.

What is HV side and LV side optimization?

LV side optimization systematically manages the peaks and troughs in the power generated in a building to reduce and stabilise the oversupply of power on the low voltage (LV) side, at the distribution point, to provide the optimum voltage.

LV side optimization is an effective means of correcting a building’s incoming voltage issues.

HV side optimization works on the same principles as LV side optimization, however it optimizes the supply of electricity on the high voltage side – before it even enters a site.
The ability to reduce energy consumption, costs, and carbon emissions is maximised by employing the technology on the HV infrastructure and correcting the issues of excess power at the source.
If there’s an opportunity to correct the voltage before it even enters the site, if the building has its own HV transformers for example, then it makes sense to do so as this ensures the benefits of voltage optimization are maximised.

How does the HV MAX system differ from other voltage optimization systems in the Powerstar range?

Apart from the obvious variation of correcting the voltage on the HV side rather than the LV side, Powerstar HV MAX inherits a number of other distinct benefits and variants.

Powerstar HV MAX is built on a super low-loss amorphous core transformer that replaces a building’s existing transformer to correct the voltage supply as it enters the site.

Simply replacing the HV transformer, with a super low loss amorphous core transformer will provide savings of between 3-10% compared to traditional transformers, along with reduced transformer losses.

Powerstar HV MAX also combines Powerstar’s existing electronic-dynamic voltage optimization technology to provide a further 12-15% saving. Therefore the expected savings from Powerstar HV MAX could range from 15% to 25%.

What type of companies have installed Powerstar?

In the UK Powerstar clients include large blue chip companies such as ASDA and Punch Taverns, alongside government departments, local authorities and the NHS.

Internationally the company is also expanding its presence with the signing of distribution agreements to supply Powerstar in Greece, Malta, Spain, Poland, South Africa and the UAE along with with the EMSc UK Ltd international offices in Cyprus and Australia.

We have case studies and testimonials available on this website from a selection of our clients who have had the voltage optimization system installed.

Below are a selection of some of our results, showing savings gained in energy consumption through installation of the Powerstar voltage optimization system:-

Guoman Hotels Group Ltd – Thistle Hyde Park Hotel 26.1% saving

British Apparel & Textile Federation 16.3% saving

Confederation of British Metalforming 21% saving

Punch Taverns – Lincoln Public House 24% saving

Purification Products Ltd 23% saving

TEV Ltd 17.8% saving

NHS – Scott Clinic, Mersey Care, NHS Trust 18% saving

Cornwall Council – Waterwold Newquay 13% saving

Richmond Community College 16.1% saving

Oxley Threads (Now Amann Group) 17.7% saving

Is voltage optimization suitable for new buildings?

Yes, voltage optimization is able to deliver energy savings in new buildings, refurbishments or existing sites. Powerstar have a dedicated new build division, established to assist new build projects with implanting voltage optimization at their site. Visit the new build section of our website and download the new build product brochure for further information.

Are Powerstar and EMSc the same company?

Yes, Powerstar is a voltage optimization product designed and manufactured by EMSc (UK) Ltd.

EMSc is an engineering market leader renowned for the innovative design of the ‘Star’ range of energy solutions. These include Powerstar, Airstar, Lightstar, Hotelstar, Motorstar and Autostar.

Powerstar is the flagship product in the EMSc catalogue, a voltage optimization system that optimizes the voltage supply to buildings and equipment. Information on the full range of ‘Star’ products designed by EMSc can be found on the EMSc UK Ltd information site.

Does Powerstar / EMSc manufacture the units?


The voltage optimization systems are designed and manufactured at our Sheffield based workshop. All transformer components are UK manufactured under BS171 IEC60076.

Powerstar components including minor items such as the paint are sourced from UK manufacturers and Enhanced Capital Allowances can be claimed.

Powerstar has been awarded the prestigious Made In Sheffield accolade in recognition of the manufacturing quality of the voltage optimization product.

Made in Sheffield has become one of the world’s great brands, internationally recognised as a mark of origin and quality on the city’s manufactured products. In order to be awarded the mark a company must first demonstrate their commitment to producing high-quality products.

Does the unit have circuit protection as standard?

The Powerstar will always have incoming circuit protection as standard.

If possible, we will utilise existing protection or install new protection. In either instance the protection will be rated to the installed Powerstar system.

As part of the installation process we will always ensure that discrimination is never compromised therefore incoming circuit protection is always essential.

Does the unit require any maintenance?

The Powerstar voltage optimization system has 100% reliability. The (fixed) Powerstar system has no moving parts, therefore no maintenance is required.

Is there a need for cooling?


The unit is naturally ventilated within its enclosure and submits minimal sound and vibration while operating with a maximum heat output of 5 degrees (celcius) above ambient. As the Powerstar voltage optimization system is situated in an IP23 enclosure, this acts as the minimum distance required from where people are working.

How do Powerstar calculate savings?

When calculating the savings following an installation of Powerstar voltage optimization we offer two options:

1) HHD – Our recommended savings calculation option, that compares half hour data over a three month period from before and after the installation.
This also takes into consideration any changes to the site loading, weather affected loads and how these would affect electricity consumption.

2) Independent verification – Savings results are independently verified by the University of Sheffield statistics department. An accuracy of +/- 1% is guaranteed.

How much can voltage optimization save?

Savings will vary dependant on the individual site – that’s why we always carry out a full site survey first to determine the exact electrical loading characteristics.
In our experience, for a 5% voltage reduction we expect at least 10% in energy savings.

Voltage optimization provides savings in the inductive electrical loads within buildings. Inductive loads being motors, pumps, fans, IT equipment (switch mode supplies) and lighting (non high frequency).

The actual energy consumption savings that can be achieved will completely depend on the electrical loading characteristics of a particular building. A building which has fixed speed devices such as air-handling units, multi stage compressors, pumps and standard switch start fluorescent fittings will achieve higher savings than a building with high frequency lighting, VRV (VSD controlled) chillers and VSD controlled air-handling units.

Powerstar has recorded savings of up to 26.1% in energy consumption, as evidenced in the Guoman Hotel Group Management study.
On average Powerstar saves between 12%-15% on annual energy consumption.

Where can I expect to see the best savings from voltage optimization?

Voltage optimization works best on inductive loads – motors and lighting for example – and significant savings can be achieved on motors in particular, especially if these are not loaded at 100% of the their capacity for 100% of the time.

How long does it take to start making savings from Powerstar?

Once Powerstar is installed, energy savings are instantaneous.

Savings can be monitored by the client themselves via the HMI (human machine interface).

Post installation the client will also be provided with a full savings report which will identify the savings achieved from the installation of the Powerstar voltage optimization system.

Savings will be verified internally and externally.

What is involved in the site survey carried out for Powerstar?

To fully establish the correct solution for each site, an in depth site survey must be completed. The survey is carried out by a qualified engineer who is able to effectively qualify the initial information gathered during the evaluation stage.
Powerstar survey’s are split into three parts:
1) Installation evaluation
The installation section of the survey will look at space restrictions and circuit protection. The information from this part of the survey will be assessed to provide the client with a detailed cost for installation and to inform them where the best location is to locate the Powerstar voltage optimization system on site.
2) Determine the voltage profile on site
By analysing the on-site voltage profile it enables the correct voltage optimization system and the correct optimization settings to be identified, whilst ensuring that all equipment on site will continue to work following the installation of Powerstar.
A minimum of six spot readings are taken on site to determine where the lowest voltage occurs, the voltage drop on the supply and if there are any voltage issues on the supply.
3) Non-eligible load breakdown
The non-eligible load breakdown identifies the loads within a site that will benefit from Powerstar voltage optimization and loads within a site that will not benefit from voltage optimization.
The non-eligible loads are detailed to the client in the proposal and taken into consideration, along with the voltage optimization setting, when calculating a kWh saving percentage. This percentage is used to calculate the payback period and Return On Investment percentage for the client.

How long does the entire process of installing Powerstar take?

The overall process of installing Powerstar, from enquiry through to completion involves a number of key steps.

The shortest completion of all necessary steps from evaluation through to install would be around the 2 month mark.

More information on the key steps involved can be found via How we work

Do you use external contractors to install Powerstar?

Either our own installation team or approved sub contractors will be responsible for installation of the Powerstar voltage optimization system. (All are NICEIC registered and have undergone a competency verification procedure). A list of current approved subcontractors is available on request and we may use any one of them to install Powerstar on your site.

After discussions with the client a delivery date and time is arranged. Appropriate transportation is arranged and the installation team will be on site to receive the delivery of the Powerstar unit and transport this to the install location.

The installation team will remove the packaging from the Powerstar unit and remove from site, recycling material where appropriate.

What is the guarantee period for Powerstar?

Powerstar voltage optimization systems come with up to 15 years warranty.

We guarantee 100% of the savings quoted as a percentage of kWh, as per our proposal.
Our warranty includes parts and labor. Alternatively, in the case that we promise for example 10% but you achieve 9% we will provide a one-off payment to compensate for the loss.

How much does Powerstar cost?

Each Powerstar unit is made to measure, with each unit varying according to site characteristics. For this reason, a set price can not be ascertained until a full site survey and analysis have been carried out. Please contact us to arrange an evaluation



Powerstar strengthens its market leading position with acquisition of UK manufactured transformer company Bromsgrove Winding Services Ltd

Powerstar, the market leading voltage optimisation and energy storage brand has completed the acquisition of Bromsgrove Winding Services Ltd (BWS) and strengthened its portfolio of products and services. As a trusted name for providing engineering led solutions to contribute towards businesses efficiencies, cost savings and Corporate Social Responsibilities (CSR), this acquisition will help Powerstar to...