Electric vehicle charging stations: four trade-offs that secure your
Four technical trade-offs structure your EV charging sizing
A poorly sized charging station costs more in Enedis meter reserve than in hardware: EV charging infrastructure operating overruns most often stem from initial undersizing, not from the choice of charging stations. For an Energy Manager committed to a trajectory of reducing tertiary-sector consumption, the real trade-off is not 7.4 kW versus 22 kW, it is the scalability of the upstream supply over 10 years. Kytom has been designing and installing your charging infrastructures since 2006, with a typical lead time of 12 weeks depending on the electrical upgrades required. Our Qualifelec IRVE level 2 qualification covers the obligations arising from decree no. 2017-26 and the LOM law, with more than 1200 projects delivered from our 11 agencies in France and Spain. In concrete terms, we secure four technical decisions that determine the trajectory of your tertiary-sector consumption: unit power versus density of points, scalable meter reserve, single- or three-phase balancing in accordance with NF C 15-100, interface with the existing main LV switchboard. Here is how we structure these trade-offs, where we see recurring mistakes, and in which cases our integrated approach is not justified.
The framework
EV charging sizing involves four trade-offs rarely addressed together at the preliminary design stage. This is where most of your 10-year operating cost is decided.
Unit power versus density of points. 6 charging stations at 7.4 kW serve more long-charge users than a fleet of 3 charging stations at 22 kW for an equivalent budget, but they saturate the switchboard during the morning peak. On our sites, 7.4 kW charging stations cover the vast majority of office uses (parking longer than 4 h) with significantly less switchboard saturation. The market over-values 22 kW as a future-proof standard, wrongly so in office tertiary settings.
5 to 10-year scalability. Anticipating fleet growth requires reserving a significant power margin at the meter from the design stage, otherwise costly upgrades will be needed post-installation. True scalability is decided on the upstream meter reserve, not on the charging station’s unit power.
Single- or three-phase balancing. The mix of light vehicles (7.4 kW single-phase) and utility vehicles (11 or 22 kW three-phase) determines phase distribution in accordance with NF C 15-100. An imbalance overlooked at the design stage is paid every month on the supplier bill.
Interface with the main LV switchboard. Direct connection or dedicated EV charging sub-meter: this choice determines your billing that can be passed on to occupants and the exclusion of mobility kWh from the baseline.
Scalable infrastructures represent an additional initial installation cost, but significantly reduce the total cost of ownership over ten years by avoiding costly upgrades.
Your risks
Three mistakes account for most post-installation upgrades
Across the EV charging projects delivered by Kytom, three mistakes account for most costly upgrades. They directly affect the energy consumption reduction trajectory set for tertiary-sector buildings.
Undersizing the upstream supply. Planning only for instantaneous power without anticipating growth forces a complete overhaul of the electrical switchboard as soon as 2 or 3 charging stations are added. Quantified consequence: an unbudgeted increase in Enedis subscribed power (€1,500 to €25,000 depending on the tier) and a 12 to 18-month delay in your tertiary-sector reduction objective.
Phase imbalance in three-phase systems. Uneven distribution of single-phase charging stations across L1, L2, L3 causes nuisance tripping of the main circuit breaker and supplier penalties on the power factor, visible every month on your energy bill.
Layout not coordinated with traffic flows. Positioning charging stations without mapping deliveries and accessible parking spaces generates permanent usage conflicts and ground-marking rework.
The trap no one flags. EV charging consumption appears in your annual declaration as soon as it is supplied by the building’s meter. Dedicated EV charging sub-metering is not a management convenience, it is a prerequisite for excluding these kWh from the reduction baseline under mobility uses. An EV charging project without sub-metering mechanically penalises your -40% trajectory by 2030.
Our safeguard: a usage audit before design, whose cost represents a modest fraction of the overall project and which helps avoid most costly post-installation upgrades.
Commercial honesty
When our integrated approach is not justified
Our full method is not universally justified. Two configurations call for lighter sizing, and we tell you so frankly during the audit phase.
Fleet of fewer than 6 points with no growth prospects. If your site is stable (permanent headquarters, no company vehicles planned within 5 years), over-reserving meter power generates an oversized Enedis subscription whose annual extra cost exceeds the savings from avoiding future upgrades. Strict sizing based on current use remains preferable. In that case we calibrate a 2 to 4-point installation with no scalable reserve.
Meter reserve already comfortable (above 50 kVA) for fewer than 4 points. A structured forward-looking audit becomes disproportionate. A simple main LV switchboard reading is enough, and commissioning a 10-year usage study adds to the total cost with no measurable benefit.
In both cases, we steer towards a short intervention: main LV switchboard reading, targeted quote, installation and Consuel, with no forward-looking study phase. Our commitment: to tell you when our integrated method adds value, and when it would represent an unjustified extra cost for your situation.
Method
- Upstream technical audit
We measure the power available at your Enedis delivery point, the condition of the main LV switchboard, the residual capacity of the cable trays and the earthing constraints. This technical snapshot determines everything else: without it, the risk of post-installation upgrade rises from 20% to 80% across our portfolio. Deliverable: EV charging capacity note, within 2 weeks. - Forward-looking usage study
We map your current needs (fleet, frequency, parking durations) and project a 5-10 year trajectory incorporating the regulatory obligations applicable to tertiary-sector buildings and car parks. This projection determines whether we reserve 30 to 40% additional power or whether we size strictly to current use. Deliverable: quantified scenarios with avoided upgrade cost. - Integrated power and civil works design
We optimise the trenches, coordinate with existing networks and choose the appropriate laying method (cable trough, drawn-in conduit, technical trunking). The design-build integration eliminates the back-and-forth between electrician and civil engineering, which adds 3 to 5 weeks in separate lots. Deliverable: power execution drawings, civil works drawings, detailed schedule. - Charging station and supervision technology selection
We favour the OCPP 1.6 J or 2.0 protocol depending on your operating roadmap, to guarantee multi-operator interoperability and compatible energy supervision. In 90% of tertiary cases, OCPP 1.6 J is sufficient and opens up a wider catalogue of charging stations. Deliverable: charging station shortlist, supervision architecture, occupant re-billing plan. - Coordinated execution and Consuel
We orchestrate the installation, progressive commissioning, Consuel certification and user training. Target lead time: 6 to 10 weeks versus 12 to 16 in separate lots. You receive an installation compliant with NF C 15-100, qualified Qualifelec IRVE level 2, and an onboarding kit for your occupants.
