Why does it matter if my system is classed as HV?

If your system is classed as HV, you have stricter safety, maintenance and competency requirements, so it must be managed by suitably trained specialists.

How is HV different from LV in the UK?

LV covers everyday supplies like 230 V and 400 V, while HV operates at much higher voltages and needs specialist equipment, controls and procedures.

Do I have HV equipment on my site?

If you have a private substation, incoming 11 kV supply or ring main units, you probably have HV equipment and should seek professional advice.

Who is responsible for maintaining HV equipment?

Responsibility is usually defined in your supply agreements. Site owners often control and maintain their own HV assets, with support from specialist contractors.

Can my in house maintenance team work on HV systems?

Only if they are properly trained, authorised and equipped. Most businesses use specialist HV contractors like Lyons Electrical for this work.

How often should HV equipment be tested?

Intervals depend on equipment type and environment, but HV systems are typically inspected and tested on a regular planned schedule agreed with your contractor.

What are the risks of poorly maintained HV systems?

Poor maintenance can lead to insulation failure, arc flash, fire, unplanned outages and serious safety incidents that may breach legal duties.

Will HV work disrupt my operations?

Some HV work needs planned shutdowns, but careful coordination, out of hours work and temporary supplies can reduce downtime.

Can Lyons Electrical design a new HV installation?

Yes, Lyons Electrical can design, install and commission new high voltage systems tailored to your site, load and future expansion plans.

Can you upgrade old HV switchgear?

We can assess existing HV switchgear, advise on condition and safety, then plan upgrades or replacements that improve reliability and compliance.

Do I need HV for EV chargers or solar?

Large EV charging schemes and solar farms can affect HV supplies. Lyons Electrical can confirm whether your project impacts the high voltage side.

How do I know if my supply includes HV equipment?

Signs include on site substations, 11 kV labels, ring main units and agreements mentioning high voltage. We can review documents to confirm this for you.

What information helps before an HV survey?

Single line diagrams, previous test results, supply agreements and access details all help us plan a safe and efficient HV survey.

Can you work with our DNO during HV projects?

Yes, Lyons Electrical routinely liaises with UK distribution network operators to coordinate shutdowns, new connections and protection settings.

Is high voltage always on the customer side of the supply?

Not always. In some cases the DNO owns the HV equipment. We help you understand where the boundary of responsibility sits on your site.

What is the first step if I am unsure what is classed as HV in the UK on my site?

Contact Lyons Electrical with your site details. We can review drawings, visit your site and explain clearly which parts are classed as high voltage.

Can Lyons Electrical help with both HV and LV systems?

Yes, we work across high and low voltage, so we can design and maintain a complete solution from your HV intake down to final circuits.

How do HV regulations affect my business?

Regulations require HV systems to be designed, operated and maintained safely by competent people. We help you comply through design and ongoing support.

Why choose Lyons Electrical for HV work?

Lyons Electrical offers practical advice, end to end project delivery and clear communication, helping you manage high voltage systems with confidence.

HV Or Not? What Is Classed As HV In The UK

Q: What is classed as HV in the UK?

In the UK, high voltage usually refers to systems operating above standard 400 V three phase supplies, often in the 3.3 kV to 33 kV range.

Lyons Electrical
Dec 3, 2025
4 min read

What is classed as HV in the UK?

If you are planning new infrastructure, upgrading your supply, or taking over a commercial site, it is natural to ask what is classed as HV in the UK. HV simply stands for high voltage, but where that line is drawn matters for safety, compliance, and how your system should be designed and maintained.

In simple terms, low voltage in the UK usually refers to the supplies most businesses know already, such as 230 V single phase and 400 V three phase. High voltage covers systems operating much higher than this, commonly in the 3.3 kV, 6.6 kV, 11 kV or 33 kV range. You do not need to remember the exact figures. What matters is whether your site has equipment that operates at these higher levels and therefore needs specialist HV expertise.

If you have a private substation, an incoming 11 kV supply from the network operator, or your own ring main feeding multiple buildings, it is very likely that part of your installation is classed as high voltage. When clients ask what is classed as HV in the UK for their particular site, our priority is to translate the technical details into clear, practical advice.

Why HV classification matters for your business

Understanding what is classed as HV in the UK on your site is not just a technical detail. It affects your legal responsibilities, your maintenance strategy, and even your insurance.

Diagram explaining what is classed as HV in the UK for businesses

Safety and compliance first

High voltage equipment carries a much greater potential for serious injury, arc flash and damage if something goes wrong. UK regulations expect HV systems to be managed by competent, trained people working to formal procedures. That typically includes documented switching rules, permits to work and a clear definition of who is in control of each part of the system.

If you are responsible for a site with high voltage equipment, you need to know where your duties start and end. Lyons Electrical helps duty holders, facilities teams and business owners understand which parts of their network are classed as HV and what that means day to day.

Reliability and continuity of supply

HV networks often sit at the heart of a site’s power infrastructure. When they fail, the whole operation can go down. Correctly specified high voltage switchgear, transformers and protection settings reduce the risk of unplanned outages, increase asset life and keep your production or services running smoothly.

By identifying what is classed as HV in the UK within your network, we can advise on condition, risk and practical steps to improve reliability, from routine testing to planned upgrades.

High voltage switch room showing clearly labelled UK HV equipment

Typical HV equipment you might have on site

Many businesses are not completely sure what equipment they have. You may only see a locked metal room marked “Substation” or an outdoor compound with “Danger of Death” signs. Behind those doors could be your private high voltage network.

Common HV assets include incoming 11 kV supplies, ring main units, HV switchboards, transformers that step voltage down to 400 V, and associated protection and metering. If your site has more than one building fed from the same intake, or you share an HV supply with other units on an industrial park, then high voltage is almost certainly involved somewhere.

Lyons Electrical can review your single line diagrams, as-fitted drawings and network operator information. From there we explain clearly what is classed as HV in the UK for your installation and which parts sit under your control rather than the local DNO.

How Lyons Electrical supports HV systems

Practical advice in plain language

High voltage should not be mysterious. Our engineers talk you through your network in everyday language, whether you are planning a new connection, expanding production or simply trying to understand what you already have.

As part of our wider electrical contracting service, we design, install, upgrade and maintain HV equipment to suit your site. That might include new switchgear, transformer replacements, protection upgrades or planned shutdowns for inspection and testing. Every project is scoped around your operational needs, budget and future growth.

End to end project delivery

From the first survey to final energisation, Lyons Electrical coordinates the whole process. We liaise with the network operator, other contractors and your in-house teams so you always know what is happening and when. Our focus is on creating a safe, robust HV system that is easy to manage and document.

Because we work across both high and low voltage, we can also make sure your LV distribution, controls and plant are correctly integrated with your HV equipment. That gives you a joined up solution rather than a collection of separate jobs.

Do you need HV help or is LV enough?

You might be unsure whether your project touches high voltage at all. Perhaps you are adding large machinery, planning EV charging, installing solar, or extending an existing building. In each of these cases, it is important to understand what is classed as HV in the UK and whether your new load will affect the high voltage side of your supply.

Lyons Electrical can assess your plans, talk to the DNO where required and confirm if HV works are needed. If they are, we explain your options clearly so you can make informed decisions with no surprises.

Talk to Lyons Electrical about your HV project

Contact the team today to discuss your project, arrange a site survey or simply get straight answers to your HV questions. We are here to give you clear guidance, practical solutions and confidence that your electrical infrastructure is in safe hands.