EV charging load and substation capacity in planning

Electric vehicle charging is rarely refused on principle. What it does instead is eat electrical capacity, and on a constrained network that turns into a substation you did not plan for, a reinforcement cost you did not budget and a connection lead time longer than your planning determination. Ask the distribution network operator for a budget estimate at feasibility stage, before the layout is fixed. The answer decides whether a package substation has to appear on your site plan, and that is a planning matter even though the capacity question is not.

What the regulations already require

Part S of the Building Regulations deals with infrastructure for charging electric vehicles, and it applies to new dwellings, to residential buildings undergoing major renovation, and to new and renovated non-residential buildings with parking.

For new dwellings with associated parking, the requirement is a charge point per dwelling. For new non-residential buildings above a threshold number of parking spaces, the requirement is at least one charge point plus cable routes to a proportion of the remaining spaces. A cost cap applies to the electrical connection, above which the requirement is limited rather than absolute, and the figures and thresholds are in the Approved Document itself. Read the current edition rather than a summary, because this is an area that has been amended.

The practical consequence for planning is that charge point numbers are already controlled by another regime. A condition simply repeating Part S adds nothing and can be resisted.

Where local policy goes further

Several local plans set higher standards than the Approved Document, and in London the position is set by the London Plan, which requires a proportion of residential parking spaces to have active charging provision with the remainder passive.

Check the adopted policy and the parking standards annexe together. Charging requirements are often buried in a parking standards appendix rather than in the transport policy, and they interact with the overall parking ratio: a lower parking provision with full active charging can need more capacity than a higher provision with mostly passive infrastructure.

Where the local policy conflicts with the Approved Document, the higher standard generally governs what you have to design for, and the Energy Statement should say which one you have applied and why.

Diversified load and how it is estimated

The number that matters is not the sum of the chargers.

A hundred dwellings each with a 7 kilowatt charge point does not create a 700 kilowatt demand, because the vehicles do not all charge at once and most charge overnight over many hours. Diversity factors are applied, and the resulting figure is the basis of the connection application.

Two things push the estimate down. Smart charging, which is now the default position for domestic charge points under the smart charge point regulations, with off-peak defaults and randomised delays that spread the load. And active load management, where a controller limits total draw across the site and shares available capacity between charging vehicles.

Two things push it up. Rapid and fast chargers, which are not diversified in the same way because a vehicle occupies them for minutes rather than hours. And commercial fleet or depot charging, where vehicles do all plug in at the same time by design.

State the diversity assumption in the submission. A load figure with no stated basis is not checkable, and a network operator will apply their own assumptions anyway.

Asking the network operator the right question

Start with a budget estimate. It is inexpensive, it takes weeks rather than months, and it tells you whether the existing network can serve the load or whether reinforcement is needed.

The enquiry should give the site boundary, the total maximum demand in kilovolt amperes, the split between the base building load and the charging load, the phasing, and any load management you intend to apply. A vague enquiry produces a cautious answer, which usually means a larger and more expensive point of connection.

What comes back tells you three things. Whether a new substation is needed on site. Whether off-site reinforcement is required, and roughly what it costs. And the lead time, which in constrained parts of the network can run well beyond a year.

That last point is the one that catches development programmes. Reinforcement lead times do not compress because a contractor has mobilised, so get the enquiry in before the planning application rather than after the permission.

Siting a substation on the layout

If the answer is a new substation, it becomes a planning matter immediately.

A package substation needs a compound with hardstanding, vehicular access for a delivery lorry and a crane, clearance around the enclosure, and separation from buildings. The land is normally transferred to the network operator, so the compound has to be positioned where a permanent third party interest does not compromise the rest of the scheme.

Transformers hum. The sound is continuous, low in level and tonal, which is the combination that attracts a character correction in a BS 4142 assessment. Where the compound is close to dwellings, deal with it in the Noise Impact Assessment rather than leaving it to be raised by environmental health at consultation.

Design the enclosure as part of the scheme. A galvanised kiosk dropped into the middle of a landscaped courtyard at technical design stage is the kind of detail that generates an objection from an occupier long after the permission is issued.

Passive provision and future proofing

Passive provision is the inexpensive half of this exercise and the half most often done badly.

Useful passive provision means ducting from the distribution board to the parking space with draw cords in place, spare ways in the board, labelled terminations at both ends, and recorded as-built information. Ducting that runs to an unidentified point under a block paved car park is not provision.

Also leave headroom in the switchroom and in the substation compound. Retrofitting a second transformer into a compound sized exactly for the first one is a civils job, not an electrical one.

Consider how metering will work. On a shared car park serving flats, the arrangement for billing individual users shapes the cabling design, and changing it later is disruptive. Set it out in the Energy Statement alongside the charging strategy.

Where the site also has a heat strategy, the two infrastructure questions interact. Electrified heat and vehicle charging draw from the same connection, and the article on heat network zoning and what it means for a planning application covers where the heat side of that decision is being made for you.

Conditions and what they should not duplicate

Three condition types are reasonable here.

A condition requiring the active charge points shown on the approved plans to be installed and operational before first occupation of the relevant units. A condition requiring the substation compound to be built and screened in accordance with approved details. And, where off-site reinforcement is needed, a Grampian condition preventing occupation until the works are complete.

What is not reasonable is a condition restating Part S, or one requiring a charging strategy to be submitted when the strategy is already in the application. Offer your own wording, and point to the regulation where a condition would duplicate it.

The charging provision should also be consistent with the Travel Plan, because a plan promoting modal shift and a car park promising universal charging are telling the officer two different stories about how the site will be used.

Enter your postcode on PlanScope to see which energy and transport documents your scheme is likely to need.

This is general guidance, not legal advice; check the position with your local planning authority, your distribution network operator or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.