Why scale changes the conversation
An electric car can be charged from a circuit on the plant's switchboard. A freight truck cannot. DC equipment for heavy vehicles is quoted in hundreds of kilowatts, and a yard with several of them has the demand of a small plant.
The arithmetic is simple. Four 150 kW chargers running at the same time draw 600 kW (illustrative: 4 × 150). That power is rarely spare on a service entrance that was not designed for it; it is wise to assume it does not exist until you measure it, and to plan on having to bring it in.
That is why an electric truck project is rarely decided by the charger. It is decided by the substation that feeds it, by the contract with CFE and by the timeline of both.
The path of the energy, from the grid to the connector
The Regulations of the Electricity Sector Law (Reglamento de la Ley del Sector Eléctrico), in article 196, define electric charging for e-mobility as the installations that run from the point of connection with the grid up to the point where electricity is supplied to the charging equipment. That definition describes the real scope of the project well: everything between the CFE meter and the connector.
The e-mobility provisions issued by the former CRE (Resolution A/108/2024, chapter 4) separate the connection by voltage level. Below 69 kV it is handled with the Supplier or the Distributor; from 69 kV upward, with CENACE. In both cases they refer to the load-center connection regulatory manual (Manual Regulatorio de Conexión de Centros de Carga) of the Grid Code (Código de Red).
Expand the existing substation or build a new one
The first engineering decision is whether the yard hangs off the substation the plant already has or gets its own. It depends on four things: the real margin of the existing transformer during charging hours, the physical space, the distance between the substation and the yard, and whether the protection coordination can take the new load without being redone.
Hanging off the existing one is usually faster, because it may not require a new contract, and it almost always means managing charger power so as not to exceed the contracted demand. A dedicated substation gives independence and requires a load increase or a new connection with CFE, which is the procedure that weighs most on the schedule.
In both cases the survey of the current installation comes first. An outdated single-line diagram is the most common reason a project gets redesigned halfway through. That work belongs to substations and load increases.
Where storage comes in
A battery system between the switchboard and the chargers changes the question. Instead of drawing all the fast-charging power from the grid, the grid slowly feeds the battery and the battery delivers the peak to the trucks.
That can reduce the capacity requested from CFE, or let the yard start on the current substation while the increase is processed. It is not free and does not always apply: it works when fast charging happens in short windows with hours between them to recharge the battery. It is sized on the measured operating profile, not on the chargers' nameplate power.
What is needed for the study
From operations: how many trucks, energy per trip, how long they spend in the yard and at what times. That window decides whether slow overnight charging is enough or fast charging between trips is needed, and the difference in power is huge.
From the installation: the up-to-date single-line diagram, twelve months of bills and one week of metering at the substation. A regulatory detail worth keeping in mind: NOM-001-SEDE-2012, in article 625, excludes from the scope of charging equipment vehicles that do not travel on public roads, such as forklifts and cranes. Charging the plant's electric forklifts is treated like any other switchboard load, and is added to the same balance.
With that data the architecture is decided. It is the basis of our service for electric truck charging.
Sources
Regulations of the Electricity Sector Law, DOF October 3, 2025, article 196.
Resolution A/108/2024, general administrative provisions on e-mobility, issued by the former CRE, DOF September 10, 2024, chapter 4. After the 2025 reform the regulator is the CNE: it is advisable to confirm the current procedure with it.
Grid Code (Código de Red), RES/550/2021, DOF December 31, 2021, load-center connection regulatory manual (Manual Regulatorio de Conexión de Centros de Carga).
NOM-001-SEDE-2012, Electrical installations (utilization), DOF November 29, 2012, article 625.
If the trucks spend the whole night in the yard and the energy they replenish fits in those hours at low power, the current transformer may be enough with load management. First measure the transformer's margin between ten at night and six in the morning: if it exists, the project becomes a switchboard project, not a substation project.
