The service entrance has three limits, not one
When someone asks how many chargers fit in their plant, they usually think of the transformer. It is the first limit, but not the only one. There are three, and the lowest of them sets the project.
The first is physical capacity: the transformer's kVA, the size of the feeders and the capacity of the switchboard that will take the new circuits. The second is contractual: the demand you have contracted with CFE. The third is economic, and it is the one almost nobody checks: how much your bill goes up if the month's peak changes time or size.
The Regulations of the Electricity Sector Law (Reglamento de la Ley del Sector Eléctrico) put it in a useful way. Article 196 defines 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. In other words: the charger is the last piece of an installation, not the whole project.
The sum nobody does
A 22 kW AC charger looks small next to a plant's load. Ten of them no longer do: 10 × 22 kW = 220 kW if they run at the same time. Two 150 kW DC chargers add up to 300 kW, and those do often run at the same time, because they are used when there is a rush.
The right question is not how many chargers you have, but how many will be delivering power at the same time, and at what hour. That figure is added to the peak your plant already records, not to the average.
What a load peak does to your GDMTH bill
On the GDMTH tariff you pay for energy and power separately. Power is charged on the maximum demand recorded in fifteen-minute intervals, and that maximum sets the capacity and distribution charges for the period even if it lasted a single interval. We explain it in detail in how to read the demand charge on your bill.
For vehicle charging this has a direct consequence: a shift that arrives and plugs in all units at once can set the charge for the whole month. The energy those chargers delivered was small; the power they left on record was not.
There is a second effect, on the installation side. NOM-001-SEDE-2012, in article 625-21, treats charging equipment as continuous duty and requires overcurrent protection of no less than 125 % of the equipment's maximum load. A 32 A charger calls for protection of at least 40 A (illustrative: 32 × 1.25). Ten of them take up far more of the switchboard than their average consumption suggests.
Chargers that share the power
The cheapest way out is almost never a new service entrance. It is setting a cap. The e-mobility provisions issued by the former CRE (Resolution A/108/2024) define a smart charger as one that communicates through protocols such as OCPP or OCPI. In practice, that lets you set a maximum power for the whole group and have the units share it according to each vehicle's departure time.
With a well-set cap, ten chargers can coexist with the current service entrance: they do not deliver 220 kW together, they deliver what fits under the contracted demand at that moment. The cost is charging time, and in a fleet that sleeps in the yard that time is usually more than enough.
The LSE Regulations, in article 197, also allow e-mobility load centers to register as Controllable Demand (Demanda Controlable), under the provisions the CNE issues together with the Ministry (SENER). It is worth keeping in mind when choosing equipment: a charger that cannot be controlled closes that door.
What gets measured before buying
Twelve months of bills, to see each month's peak and how it compares with the contracted demand. Seven days of metering at the switchboard that would feed the chargers, to see when the peak occurs and how much margin is left in the hours when the vehicles would be plugged in.
And the vehicles' operation: how many, how many kilometers per day, what time they arrive and what time they leave. With those three pieces of data you know whether the project fits on the current service entrance with load management, whether it needs a load increase with CFE, or whether it needs a new substation.
Sources
Regulations of the Electricity Sector Law, DOF October 3, 2025, articles 196 and 197.
Resolution A/108/2024, general administrative provisions on e-mobility, issued by the former CRE, DOF September 10, 2024, item 3.6 (smart charger). After the 2025 reform the regulator is the CNE: it is advisable to confirm the current procedure with it.
NOM-001-SEDE-2012, Electrical installations (utilization), DOF November 29, 2012, article 625-21.
Structure of CFE's GDMTH tariff (energy, capacity and distribution charges). This article does not use rates.
If your measured peak plus the power of the chargers that will coincide stays below the contracted demand during charging hours, you do not need construction work: you need a well-configured power cap. Measure the peak and its time first. If it is two or three vehicles that sleep at the plant, one AC charger per unit, on a programmed schedule, is usually enough.
