Whether your premises needs a three-phase supply depends on your maximum demand, the equipment you run and what your distribution network operator (DNO) can provide. An upgrade from single-phase to three-phase usually takes several weeks to several months from first enquiry to completion, and it involves two separate workstreams: the DNO’s network assessment and connection work, and the electrical installation work on your side of the meter. This guide explains how the process works, what affects timescales and cost, and what to plan for afterwards.<\/p>\n
Single-phase is the standard 230V supply found in homes and many small shops and offices. It uses one line conductor and a neutral, with a single main fuse and a single-phase meter.<\/p>\n
Three-phase power uses three line conductors (L1, L2 and L3) plus a neutral, with three main fuses and a three-phase meter. It provides 400V between phases and 230V between any phase and neutral. Because the three phases are offset from one another, power delivery is smoother, which suits motors and larger plant.<\/p>\n
In practice, three-phase gives a much larger supply capacity than a single-phase connection and lets heavy loads be spread across three phases. Motors, commercial kitchen equipment, larger air conditioning and heat pump plant, and some production machinery are commonly designed to run on three-phase.<\/p>\n
Look at maximum demand first. If your existing single-phase supply is regularly running close to the rating of its main fuse, or new equipment would push it over, an upgrade may be needed. An electrician can carry out a maximum demand assessment using your load schedule and, ideally, logged readings.<\/p>\n
Equipment is the next test. Many larger items are only available in three-phase versions, including some commercial kitchen ranges, compressors, workshop machinery and larger heating and cooling plant. Faster AC electric vehicle chargers, such as 22kW units, also need a three-phase supply.<\/p>\n
Growth planning matters too. A fit-out, additional charging points or new plant will only increase demand. Before assuming an upgrade is the answer, have the existing supply capacity and load profile checked. Sometimes redistributing circuits or managing loads is enough.<\/p>\n
Start by identifying your DNO, the company that owns and runs the local electricity network. For most of Essex, Suffolk, Norfolk and London this is UK Power Networks, but you can confirm it from your postcode. Your energy supplier is a different company and does not carry out network upgrades.<\/p>\n
Your electrician will usually help prepare the application, including the maximum demand you need and details of any large loads. The DNO then assesses whether the local network can support the additional capacity and provides a quotation for its work.<\/p>\n
Depending on that assessment, the DNO may simply change the service head and metering arrangement, or it may need to lay a new service cable or reinforce the local network. That work happens on the DNO side of the installation, so it is carried out by the DNO or an independent connection provider, not by your own electrician.<\/p>\n
Several weeks to several months is a realistic expectation from enquiry to completion, not days. The DNO portion and the on-site electrical work run as separate stages, and the network assessment is often what sets the overall programme.<\/p>\n
Where new cables, groundworks or local reinforcement are needed, the DNO programme can extend significantly. That work sits outside your electrical contractor’s control.<\/p>\n
On-site work such as a new distribution board, submains and containment can often be planned in parallel. The final connection still depends on the DNO, so build contingency into any fit-out or equipment delivery date and start the application as early as possible.<\/p>\n
Beyond the DNO’s service head and meter, the installation side usually needs a three-phase distribution board or switchgear, new or revised submains and containment, and redistribution of existing circuits across the phases. Load balancing across L1, L2 and L3 matters, because a badly balanced installation undermines the point of upgrading.<\/p>\n
The new work must be designed, installed, inspected and tested to the current edition of BS 7671 and certified with an Electrical Installation Certificate, including schedules of circuits and test results. That gives you a clear record of what is connected where and confirms the installation is safe to put into service.<\/p>\n
Delta First’s commercial electrical contracting<\/a> team designs, installs and upgrades three-phase distribution, lighting, power and containment. For sites with plant and motor loads, our industrial electrical services<\/a> cover fault-finding and motor control work. A single accountable contractor keeps the on-site programme moving while the DNO completes its part.<\/p>\n Costs vary widely. There is no fixed UK price for a three-phase upgrade, and any figure given before the DNO has assessed the network is guesswork.<\/p>\n The main cost drivers are the DNO’s connection charges, any new service cable or network reinforcement, the distance from the network, the new distribution board and submains, containment, and testing and certification. Network reinforcement is often the largest and least predictable element.<\/p>\n Get the DNO quotation before committing to a budget. Ask for the DNO charges and the installation charges as separate line items so you can see where the money goes. That also helps when comparing contractor quotes, because the DNO element will be the same whoever does the on-site work.<\/p>\n A three-phase installation is still a BS 7671 installation, so periodic inspection and testing continues at intervals suited to the premises and its use, recorded on an Electrical Installation Condition Report (EICR). The Electricity at Work Regulations 1989<\/a> require electrical systems to be maintained so as to prevent danger. Delta First carries out commercial EICRs in Essex<\/a> with clear C1, C2, C3 and FI coding.<\/p>\n Planned maintenance catches phase imbalance and loose connections before they cause downtime. A board under uneven load runs hotter and less efficiently, so routine checks matter. Thermographic surveys are useful for spotting hot joints on higher-capacity switchgear, and Delta First can arrange them as part of a commercial electrical maintenance<\/a> programme.<\/p>\n Keep the DNO connection paperwork, certificates and schedules of circuits together with your compliance records, so the next inspector or contractor has the full picture.<\/p>\n Yes. Your electrician can usually prepare and submit the application with the load information the DNO needs, but the DNO decides what network work is required and quotes for it directly.<\/p>\n A planned shutdown is normally needed while the supply is changed over and the new installation is connected. A good contractor will plan this outside your working hours where possible.<\/p>\n Not always. 7kW chargers run on single-phase, but faster AC chargers such as 22kW units need a three-phase supply, and several chargers together may need extra capacity whichever type you choose.<\/p>\nWhat does a three-phase upgrade cost, and what drives the price?<\/h2>\n
What ongoing inspection and maintenance obligations apply after the upgrade?<\/h2>\n
FAQs<\/h2>\n
Can my electrician apply to the DNO on my behalf?<\/h3>\n
Will I lose power during the changeover?<\/h3>\n
Do I need three-phase for an EV charger?<\/h3>\n
Key takeaways<\/h2>\n
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Useful sources<\/h2>\n