Static load limiting vs dynamic load balancing

Choosing a fixed EV charging limit or a live site-capacity control without confusing the two.

Static load limiting sets an EV chargepoint to a fixed maximum current. Dynamic load balancing changes charging in response to a live measurement of the property’s demand.

Both can keep a design within an electrical-supply constraint. The difference is how much unused capacity they can recover when other loads are off.

Static limit

With a static limit, the charger never exceeds the commissioned setting. If the design can safely spare a fixed current at all relevant times, this is simple and predictable.

Its weakness is conservatism. A setting low enough for the worst credible combination of household loads can leave capacity unused for most of the night. It also depends on the maximum-demand assessment remaining valid when new loads are added.

Static control can be implemented in charger configuration, a protective controller or a site-management system. The important evidence is that the limit is access-controlled, survives restart and cannot be casually overridden through an owner app.

Dynamic limit

Dynamic control measures site import or phase current and varies EV demand around the remaining capacity. When another large load starts, charging falls. When it stops, charging can rise.

This normally needs a CT, meter or gateway at a point that sees the relevant loads. On a three-phase site it must protect each phase, not hide an overloaded phase inside a safe-looking total.

Dynamic control can deliver more energy during the same parking period, but it adds dependencies:

sensor placement and calibration
phase and direction mapping
a communications link
control response time
safe behaviour when the measurement is missing
coordination with solar, batteries and other flexible loads

Do not use vendor labels as definitions

Manufacturers use load limiting, balancing and management in different ways. A product called a “load balancer” may divide a fixed allowance between chargers without measuring the rest of the building. Another may monitor the grid connection continuously.

The operating description needs:

the measured quantity and its measurement point
whether the ceiling applies per phase, per charger or across the site
whether non-EV building demand is included
equal or priority-based allocation between chargers
behaviour after a meter, network or cloud failure

Choosing the site limit

Neither method makes an unsafe supply adequate by itself. The designer must establish the actual connection capacity, cut-out and service arrangement, maximum demand, consumer-unit capacity and circuit rating.

The setpoint may need headroom for measurement error, response delay and loads that change faster than the charger can reduce. It should also reflect DNO conditions or an agreed import capacity where those apply.

As at 22 July 2026, electrical installations should be designed to BS 7671:2018+A4:2026. The standard permits appropriate load control to form part of maximum-demand design, but the complete control and its failure state must support the assessment.

Multiple chargers

Several chargepoints can share a site allowance statically or dynamically. A fixed arrangement might give each outlet a permanent portion. A dynamic system can allocate more to vehicles that are connected, have priority or need to leave sooner.

The design should state:

maximum site and per-phase current
minimum allocation at which a vehicle can keep charging
whether a paused vehicle resumes automatically
how user priority is decided
whether an offline charger has a local cap
whether the combined fallback can exceed the site limit

OCPP can carry charging profiles between a management system and compatible chargers. It is not inherently fast or reliable enough to be the only protection for every site. A local controller or direct meter link may enforce the hard limit while OCPP handles allocation.

Solar and stationary batteries

Net grid import can be low while gross household load is high because PV or a battery is supporting the site. A control strategy based only on net import may allow charging that later becomes excessive when a cloud passes or the battery stops discharging.

The response needs to be quick enough, or reserve enough headroom, for those transitions. It should also prevent one controller charging the EV from energy another has just discharged from the home battery unless that is intentional.

Import load management is not G100 export limitation. The latter is a DNO-approved scheme controlling generation export and has separate compliance evidence.

Commissioning and later changes

Test the system by applying and removing substantial site loads, not only by viewing an idle dashboard. Confirm the charger reduces, pauses and recovers as designed, then interrupt the measurement or communications link and verify the fallback.

Record the static ceiling, dynamic site limit, sensor position and failure mode. Reassess them when adding another EV, heat pump, electric heating, PV, battery or supply upgrade.