Charging hubs and dynamic load balancing — group capacity instead of summing per charge point

The 722-ev-charging guide covers the installation requirements for an individual charge point: earthing system, RCD type, cable cross-section. This article covers what changes once multiple charge points are combined on a single connection — a charging hub at an office, apartment complex or business park — and why the connection capacity is then not simply the sum of all charge points at full power.

The problem: summing at full power is unnecessarily heavy

A charging hub with, say, ten charge points of 11 kW each would, if the connection were sized for the sum of all charge points at full power simultaneously, require a connection capacity of 110 kW. In practice, rarely do all vehicles charge simultaneously at full power — most charging sessions only partially overlap, and many users do not need full power to charge sufficiently within the available time. A connection sized for the theoretical peak demand is therefore often substantially oversized, and more expensive (both in terms of grid connection and transformer/cable capacity).

How dynamic load balancing solves this

IEC 61851-1 defines, for Mode 3 charging (AC charging with communication), a Control Pilot (CP) signal between the charge point and the vehicle, through which the charge point communicates the maximum permitted charging current to the vehicle via duty-cycle modulation. A group-level load balancing system uses this by:

Reserving a fixed, predetermined group power budget for the entire charging hub (for example 60 kW for the ten charge points in the example above, instead of 110 kW).
Distributing this group power budget in real time across the vehicles currently charging, by continuously adjusting the CP signal for each charge point to the actual available capacity.
Automatically recalculating the distribution whenever vehicles arrive or leave, so that the total group current never exceeds the reserved group capacity, not even momentarily.

Note: dynamic load balancing is an addition to, not a replacement of, the regular installation requirements from the 722-ev-charging guide — the RCD selection, earthing system and cable sizing per charge point remain fully applicable; load balancing only limits the simultaneous sum of charging currents at group level.

What goes wrong without load balancing

Without a load balancing system, the installation must be sized for the sum of all charge points at full power, or part of the charge points must be manually set to a lower, fixed power (with the drawback that this capacity also remains unused when only a few vehicles are charging simultaneously). An installation sized for the full peak demand without load balancing is functionally correct but economically inefficient; an installation connected at a lower, static power without load balancing risks overloading the main connection as soon as multiple vehicles charge simultaneously at full power.

Practical relevance

When designing a charging hub with multiple charge points, it must be established whether the connection capacity is sized for the theoretical peak demand (sum of all charge points) or for a lower, dynamically distributed group power budget — and in the latter case, it must be verified that the load balancing system never actually exceeds the group capacity, not even while individual vehicles connect or disconnect.

Common mistakes

Treating load balancing as a replacement for the individual charge point requirements (RCD, earthing, cable cross-section per charge point) — these requirements from the 722-ev-charging guide remain fully applicable; load balancing operates at group level, not at charge point level.
Setting a fixed, static power per charge point instead of dynamic distribution, and calling this "load balancing" — a static distribution does not optimally use the available group capacity and is not a full substitute for a system that redistributes in real time.
Basing the group capacity on an optimistic assumption of simultaneity without accounting for peak moments (for example all vehicles arriving around the same time) — the chosen group capacity must also remain sufficient for an acceptable charging speed under a realistic worst-case scenario.