Will the grid cope? The question your installer hopes you don't ask.

A facilities manager at an industrial site in Yorkshire took delivery of four shiny new 50kW DC chargers in February. They sat in their crates for fourteen weeks. The reason: nobody had submitted a G99 application to the local Distribution Network Operator before procurement, and when they finally did, the DNO came back with a £180,000 transformer upgrade quote as the price of connection. The installer had quoted £75,000 for the chargers and called the job done. The DNO bill — paid by the customer, not the installer — was bigger than the original project.

The villain is the installer who quotes for chargers but stays silent on grid capacity. They're not necessarily malicious. They're often just optimistic, or they assume the DNO will say yes, or they don't want to scare you off the deal. The result is the same: a project that doubles in cost in week six and stalls for fourteen weeks while the wrong solution gets unpicked.

Here's the punchline up front. That £180,000 transformer upgrade in our example wasn't necessary. The same four chargers could be installed with a Flexible Connection agreement, an Active Network Management (ANM) interface, and load management software — for zero reinforcement cost. The chargers throttle output by 11% during roughly 8 hours per month of peak grid overlap. Customers don't notice. Saving: £180,000. The DNO got paid for the application. The installer got paid for the chargers. Nobody had to buy a transformer.

This post is the conversation your installer didn't have with you in week one.

What a DNO actually does

A Distribution Network Operator owns and operates the lower-voltage distribution grid in your region — typically the network from the local substation down to your meter. There are six DNOs covering the UK (UK Power Networks, Northern Powergrid, SP Energy Networks, Electricity North West, National Grid Electricity Distribution, SSEN). Their job is to keep the local grid stable, which means they have a veto on any new connection or significant load increase.

If you install an EV charger above a certain trivial threshold, you need their permission. Two routes: G98 and G99.

G98 vs G99 — the threshold that defines your project

G98 (formerly G83/2) covers small connections — a single device of 16A per phase or less. In practical EV terms, that's a 3.6kW domestic charger or a single 7kW unit on a single-phase supply. G98 is a notification process, not an application: you (or your installer) tell the DNO within 28 days of installation. They almost never object. The connection is fast-tracked because it's small.

G99 (formerly G59) covers everything else. Multiple chargers. Three-phase chargers. Any DC fast charger. Any battery storage that can export. Any solar above 16A/phase. Almost every commercial EV install you'll ever do is G99 territory.

A G99 application is a formal process under Engineering Recommendation G99 (latest revision 2024). The DNO has 11 working days to respond with a connection offer for straightforward cases. Complex cases can take up to 65 working days. The offer details:

• Whether your existing supply can take the load (capacity headroom)
• What reinforcement, if any, the DNO requires you to fund
• What protection settings, monitoring and grid-code compliance you must meet
• Any operational restrictions on export, if you're connecting battery or solar

You can submit a G99 yourself. Your installer can submit it for you. We strongly recommend the installer does it — but only if they've actually done one before. Ask explicitly.

What trips a reinforcement quote

Three things, broadly. Get all three right and reinforcement isn't an issue. Get one wrong and you're in for an unpleasant surprise.

1. Existing supply transformer headroom. Most commercial sites run their supply at 70-85% of peak utilisation. Adding heavy EV chargers — particularly DC rapids — tips the local transformer into overload territory. Common sites: anything with industrial process load, anything with kitchen cooking load (hospitality), anything with HVAC-heavy summer profiles (offices and retail in warm regions). DNO will spot it from your half-hourly meter data and demand reinforcement.

2. Peak coincidence. Your chargers don't run flat-out 24/7, but the DNO has to assume worst case unless told otherwise. Four 50kW chargers all running simultaneously is 200kW of load. If that 200kW lands during your existing site peak, you've doubled your supply demand on paper. Reinforcement quote follows.

3. Phase imbalance and quality. Even if total headroom looks fine, large single-phase loads (rare) or harmonic distortion from rapid charger inverters can trigger DNO concerns. The DNO will quote remedial costs.

The traditional answer to all three is: pay for transformer reinforcement. £45,000 to £350,000 depending on scale and how far the work goes upstream. Twelve to twenty-six weeks of works. Sometimes road closure. Sometimes the DNO finds the wider network can't take it and you're looking at a primary substation reinforcement starting at six figures.

There is a much better answer.

Flexible Connections and ANM — the cheat code

Since 2018 every DNO has been required to offer Flexible Connection agreements alongside traditional firm connections. These changed everything for EV charging at sites with constrained supplies. Two terms to know:

Flexible Connection. A connection agreement that allows you to connect more capacity than the grid can firmly support, on the basis that your load can be curtailed at the DNO's instruction during peak periods. You pay for the capability to interrupt; the DNO doesn't pay for transformer kit they don't actually need. The trade is: you give up the right to run at full power 100% of the time in exchange for a much smaller upfront connection cost.

Active Network Management (ANM). The technical interface that lets the DNO send curtailment signals to your site automatically. Your chargers (or your EMS) listen for ANM signals and reduce output when the grid is constrained. Modern OCPP-compliant chargers and energy management platforms handle this natively.

The pattern that works for commercial sites: a Flexible Connection allows you to install 2-4x the firm capacity of your existing supply, with the agreement that you'll throttle if and when the DNO needs you to. In practice, throttling events happen for a few hours a month at most, almost always between 4pm and 8pm in winter, and your load management software can absorb the curtailment by reducing charger output by 10-15% during those windows. Drivers don't notice.

Load management as the operational layer

Even without a Flexible Connection, load management software changes the maths. The principle: your site has a peak supply limit. Your chargers can each pull up to their nameplate rating. Without management, all chargers can hit nameplate simultaneously and breach the supply. With management, the software dynamically allocates available capacity across active charging sessions, slowing some sessions to keep the site under the supply limit.

Specifically, look for these capabilities:

• Dynamic load balancing across charger groups
• Time-of-day throttling linked to a tariff or DNO ANM signal
• Vehicle prioritisation (fleet vehicles ahead of visitors, for example)
• Power capping with smooth ramp-down to avoid drivers getting "charge interrupted" warnings

The combined effect: you can connect three or four times the nameplate charger capacity your firm supply would support, because the chances of all chargers running at full power simultaneously are effectively zero — and the software guarantees they won't, even if they tried.

The worked example

Site: Industrial unit, North-West, 400kVA three-phase supply, currently running at 75% peak utilisation (peak load ~300kW). Plan: install 4 × 50kW DC rapid chargers for staff and visiting HGV drivers (200kW combined nameplate).

The naive path:

• Submit G99, DNO sees existing 75% utilisation + 200kW new load = 125% of supply capacity at peak.
• DNO offer: £180,000 transformer reinforcement (upgrade to 800kVA + cable upgrade + protection), 18-week delivery.
• Total project: £75k chargers + £180k DNO + £40k install/civils = £295,000.

The Flexible Connection path:

• Submit G99 application with Flexible Connection request and load-management commitment.
• DNO models curtailment: with site peak existing 300kW and chargers limited dynamically, the combined load only exceeds 400kVA for ~8 hours/month in winter peak windows.
• DNO offer: Flexible Connection with ANM interface, zero reinforcement, 4-week delivery.
• Site installs load management software (~£8,000) that auto-curtails chargers by 10-12% during DNO-signalled windows.
• Total project: £75k chargers + £8k load management + £40k install/civils + £0 reinforcement = £123,000.

Saving: £172,000. Project delivered 14 weeks faster. Same four chargers. Same user experience for 99.5% of charging sessions.

This isn't a clever trick. It's the standard pattern your installer should have proposed in week one. They didn't because most installers don't know how to write a Flexible Connection application, or they don't have a load management platform partner, or they make better margins selling you a £180k transformer upgrade.

What your installer should be doing in week one

A competent commercial EV installer follows this sequence — before they quote your chargers, not after:

1. Pull 12 months of half-hourly data from your supplier and analyse it for peak coincidence, load profile and headroom.
2. Confirm your DNO and check region-specific connection charging methodology (ECCR — Effective Connection Charging Rules).
3. Calculate two scenarios: firm connection requiring reinforcement, vs Flexible Connection with load management. Present both with capex and timeline.
4. Submit G99 in week one if proceeding, not week six. The clock starts when the application lands, not when you decide.
5. Specify load management software in the original quote, not as an upsell when reinforcement quotes come in.
6. Pre-engage with the DNO for any site over 200kW of new load. A 20-minute phone call in week one saves four weeks of formal back-and-forth later.

If your installer can't do all six, you're hiring the wrong installer.

The short version

DNO applications fall into G98 (single small unit, notification only) and G99 (everything commercial, formal application, 11-65 working days). The default fear scenario — reinforcement costs of £45k to £350k+ — is often avoidable with a Flexible Connection agreement plus ANM interface plus smart load management software. Our worked example saved £172,000 against the naive transformer-upgrade path on a 4 × 50kW rapid install. Get your G99 in week one, not week six, and demand that your installer model both firm and flexible scenarios before they quote the chargers. The DNO bit isn't the project killer it's made out to be. The installer who doesn't talk about it is.

Want us to do the maths on your site?

Book a site survey at /site-survey. We'll pull your half-hourly data, talk to your DNO before we touch a charger spec, and model the Flexible Connection scenario against the firm one. With real numbers in pounds. (Including the bit about the £180k transformer. Especially that bit.)