WhyEVChargingIsanLVProblemFirst
The EV charging conversation in commercial property is dominated by the government mandate and the charger manufacturer's specification sheet — both start at the car park, neither starts at the LV board. Properties are being quoted for EV charger installations their electrical infrastructure cannot currently support, and the gap goes unraised because nobody present has an incentive to flag it. An installation of 20 × 7kW chargers adds 40kW of continuous load to your building: an engineering question that must be answered before a planning application is submitted, a charger manufacturer is approached, or a cable route is excavated.
The main LV distribution board is the starting point for any EV infrastructure assessment. The fundamental question is available spare capacity — the difference between the board's rated current and the installation's current maximum demand. A board operating at 85–90% of its rated capacity has no meaningful spare capacity for additional continuous loads, and any charger installation requires either a new supply, a diversity management solution, or a board upgrade before a single charger can be specified.
EV chargers do not behave like typical office equipment. Where vehicles charge overnight, multiple charger sessions overlap in the same window, eroding the diversity factor the distribution system was designed around. Smart charging manages this through demand scheduling — but the aggregate peak demand must still be within the LV infrastructure's capacity after smart charging is applied.
LV Board Capacity First
Available spare capacity — the difference between the board's rated current and current maximum demand — determines what EV infrastructure is possible before a charger is selected or a cable is routed.
DNO Engagement Timeline
Installations above 69kW require DNO notification under G99/G100. Above 100kW, a formal connection application and capacity assessment applies — start this process before any programme commitment, not after.
Smart Charging Compliance
EV Smart Charge Points Regulations 2021 mandate smart charging functionality for all new domestic and commercial installations. Aggregate peak demand must be within infrastructure capacity after scheduling is applied.
Sub-Metering Architecture
Fleet reimbursement, tenant billing, and HMRC compliance each require specific metering design — these are infrastructure inputs that determine board architecture, not incidental considerations.
LV Capacity and Diversity Assessment
The capacity arithmetic is specific: a board rated at 400A with a measured maximum demand of 340A has approximately 60A of theoretical spare capacity — enough for one or two 7kW chargers before demand management is considered. That is a relatively favourable starting position. Many commercial buildings operate closer to their rated capacity, particularly older premises where load has grown through incremental additions of IT infrastructure, air conditioning, and catering equipment.
Worst-case simultaneous demand is the design scenario that matters most. A car park with 20 chargers installed but only 10 in simultaneous use on any given evening may look manageable under diversity. But the design must account for the realistic worst case — arrival timing during peak evening hours, vehicles with low state of charge all connecting simultaneously, smart charging schedules that concentrate load in the same off-peak window. The smart charging system shapes demand, but it does not eliminate the need to design for the peak it will produce.
Infrastructure Thresholds and Compliance Standards
LV Infrastructure Thresholds
- Load per 7kW AC charger
- 32A single-phase
- Load per 22kW AC charger
- 32A three-phase
- Smart charging mandate
- Mandatory above 3.5kW — EV Smart Charge Points Regulations 2021
- DNO notification threshold
- 69kW aggregate (approx. 10 × 7kW chargers) — Engineering Recommendation G99/G100
- DNO formal application trigger
- Above approx. 100kW — network capacity assessment required; allow several months
Sub-Metering Requirements
- Cost recovery categories
- Fleet reimbursement, tenant billing, energy cost recovery, DNO reporting
- HMRC compliance
- Accurate metering required where workplace charging is an employee benefit — determines taxable value
- Board architecture implications
- Dedicated EV charging distribution board, sub-main cable from main switchboard, metering equipment, CPMS communication links
What This Guide Covers
- 01LV board capacity assessment — rated current, current maximum demand, and available spare capacity
- 02DNO engagement process — notification requirements under G99/G100 and connection application timeline
- 03Cable route planning — sub-main routing from LV switchroom to car park charging zones, groundworks, and fire-stopping
- 04Sub-metering architecture — board design for fleet reimbursement, tenant billing, and HMRC compliance
- 05Future-phase provision — oversized EV board, pre-installed trunking and ducting sized for ultimate charging capacity
- 06Smart charging compliance — EV Smart Charge Points Regulations 2021 and worst-case simultaneous demand design
Common Planning Failures and How to Avoid Them
Infrastructure Capacity Gap Discovered After Commitment
Challenge
Properties commit to EV programmes — and in some cases submit planning applications or approach charger suppliers — before an LV assessment has been completed. When the infrastructure gap is identified mid-project, the cost and programme implications are at their worst: a board upgrade or new supply cannot be accelerated to meet an already-announced programme.
Solution
Commission an LV infrastructure assessment before any programme commitment is made. The assessment covers board spare capacity, supply configuration, DNO obligations, and cable route options — it is the prerequisite that determines what the programme can credibly promise.
DNO Programme Delay from Late Engagement
Challenge
DNO engagement for installations above 69kW is the single most common cause of programme delay in commercial EV projects. When notification under G99/G100 is initiated after a stakeholder programme has been communicated, the months-long DNO assessment process — and any resulting requirement for grid reinforcement or a demand management agreement — cannot be absorbed without slipping the committed dates.
Solution
Start DNO engagement before any programme commitment is made to stakeholders. For larger installations above approximately 100kW, initiate the formal connection application process at the same time as the feasibility assessment, not after a contractor has been appointed.
Cable Route Cost Underestimated at Outset
Challenge
Clients and programme managers typically focus planning attention on charger specification and quantity. The sub-main cable route from the LV switchroom to car park charging locations — through occupied buildings, across ceiling voids, down risers, and potentially involving excavation and reinstatement across car park surfaces — is frequently the largest single cost element and the one most likely to carry a programme risk that was not modelled at the outset.
Solution
Include cable route survey and groundworks assessment in the initial feasibility scope. Where resurfacing or major access works are already planned within 12–18 months, design EV cable ducting provision into that programme — the marginal cost is a fraction of excavating a completed surface retrospectively.
8-Question Infrastructure Guide
Step 01
What is the rated current of your main LV distribution board and what is your installation's current maximum demand? Available spare capacity is the baseline
if there is none, your options are a new supply, load management, or a board upgrade before any charger is specified.
Step 02
Has your installation had an Electrical Installation Condition Report within the last five years? An EICR surfaces existing deficiencies that must be resolved before adding new continuous load. Proceeding without one means adding EV load to an infrastructure whose condition is unknown.
Step 03
Does your site have a three-phase supply to the LV board? Three-phase supply is required for 22kW AC chargers. Single-phase sites are limited to 7kW per charger
and if the aggregate load of multiple 7kW chargers exceeds board capacity, a supply upgrade may still be needed.
Step 04
What is the distance from the LV switchroom to the proposed charger locations? Cable route length directly affects conductor sizing, voltage drop calculations, and installation cost. Charger zones in remote car parks, separated from the building by roadways or landscaping, can make cable routes a dominant cost driver.
Step 05
Are there existing cable ducts, containment routes, or service trenches to the car park? Existing ducting eliminates groundworks. Its absence means trenching, reinstatement, and programme time
often the element that most surprises clients who have focused their planning on the charger cost.
Step 06
Is your aggregate planned charging load above 69kW? Above this threshold, DNO notification under G99/G100 is required. Above approximately 100kW, a formal DNO connection application and network capacity assessment may apply
allow several months, and start the process before any programme commitment is made.
Step 07
Do you need sub-metering for fleet cost recovery, tenant billing, or HMRC compliance? Sub-metering requirements determine the distribution board architecture and communications design
they affect how the main switchboard needs to be configured, not just where the charger sits in the car park.
Step 08
Is any car park resurfacing, landscaping work, or major access works already planned within the next 12–18 months? Installing EV cable ducts during planned groundworks is significantly more cost-effective than excavating a completed surface. If resurfacing is planned, design the EV ducting provision into that programme now.
Infographic
NEXGEN ELECTRICAL · EV CHARGING INFRASTRUCTURE GUIDE
The Commercial EV Charging Infrastructure Guide
8 questions every property manager must answer before commissioning EV chargers — covering LV board capacity, DNO thresholds, smart charging mandates, and sub-metering requirements.
nexgen-electrical.co.uk/ev-charging-infrastructure-guide.pdf
Download the free 8-question infrastructure guide: nexgen-electrical.co.uk/ev-charging-infrastructure-guide.pdf
Key Takeaways
- 01An EV charger installation is an LV infrastructure project first — the charger is the last item specified, not the first; the LV board determines what is possible
- 0220 × 7kW chargers adds 40kW of continuous load to your building — check board spare capacity before approaching any charger supplier or programme manager
- 03Smart charging is mandatory above 3.5kW and manages demand peaks, but does not eliminate them — aggregate peak demand must still be within infrastructure capacity after scheduling is applied
- 04DNO engagement for installations above 69kW can take several months — start it before making any programme commitments to stakeholders, not after
- 05Sub-metering requirements (fleet reimbursement, tenant billing, HMRC) are infrastructure design inputs that determine board architecture — they are not incidental to the charger installation
- 06Provision for future phases at the design stage — oversized EV board, pre-installed ducting — costs a fraction of retrospective reinforcement in a finished car park
Client Testimonial
The question we hear most often is 'can we add chargers to our car park?' The correct first question is 'what can our LV board currently support?' The answer to the second question determines whether the first is straightforward or a full infrastructure project.
Commission the Assessment First
The commercial EV charging market has a structural communication problem. Charger manufacturers sell chargers. Charge point management software providers sell software. Installation companies quote installation. Very few parties in those conversations have an incentive to raise the LV infrastructure question early — because doing so complicates the sale, extends the programme, and may require work that the party raising it is not equipped to deliver. The consequence is that property managers and fleet managers are committing to EV programmes against a backdrop of infrastructure constraints they were not told about, discovering them mid-project when the cost and programme implications are at their worst.
The DHL Reading Distribution Hub project illustrates what an LV infrastructure designed with headroom looks like in practice. The 800A TPN main distribution board Nexgen installed isn't solely the power supply for today's conveyor systems — it is the electrical backbone that supports future load growth across the facility, including EV infrastructure as DHL electrifies its fleet operations. Infrastructure designed with future capacity in mind is always cheaper than infrastructure retrofitted under pressure. The principle applies as directly to a commercial car park as to a distribution warehouse.
The eight questions in this guide are a structured starting point, not a substitute for a full assessment. A commercial EV charging feasibility study by a qualified LV engineer — covering board capacity, DNO requirements, metering architecture, cable routes, and phasing strategy — costs a fraction of the downstream expense of identifying an infrastructure gap after a programme commitment has been made and a car park has been dug up. Commission the assessment before you commission the chargers.
