Large-consumer connections — indirect metering via current transformers

A horticultural business with assimilation lighting, climate installations and its own CHP generation (see the CHP grid connection guide) often has a connection that lies far above the threshold of a regular "small-consumer" connection. From a certain connection capacity onward, not only the tariff and market model changes, but also the way of metering itself.

The threshold: greater than 3×80A

Connections larger than 3×80A fall under "large consumer" in the Netherlands and, unlike small-consumer connections, are not metered directly. Instead, the electricity meter is connected indirectly via current transformers (CTs): the main current does not flow through the meter itself, but through the primary winding of the CTs, which pass a reduced, proportional secondary current to the meter.

Why indirect metering is needed

For large-consumer connections, the currents are too large to run practically and safely straight through a meter (both in terms of the meter's construction and safety during replacement/maintenance). Current transformers make it possible to reduce a large primary current to a standard secondary value (often 1A or 5A) that a regular meter can process safely and accurately.

Accuracy class

The current transformers applied must, in terms of accuracy class, match the requirements of the main connection: the combination of CT and meter must deliver a reliable, verifiable measurement across the full expected load range of the connection. The specific requirements for CTs (accuracy class, transformation ratio, load capacity) and for the indirect metering setup as a whole are laid down by Netbeheer Nederland in the Meetcode Elektriciteit.

Note: the precise transformation ratio and accuracy class per CT follow from the design of the specific connection (by the grid operator/metering-responsible party) — this article gives the principle, not a universal figure that applies to every connection.

Practical consequence for the installation owner

The metering equipment (CTs + meter) is installed/managed by the metering-responsible party (often the grid operator or a recognised metering service), not at the discretion of the installation owner.
On extension or modification of the connection (for example by adding own generation such as CHP or battery storage), the metering setup must be reassessed — a CT that was correctly sized for the old situation may no longer be so for a new load or feed-back situation.

Common mistakes

Assuming that a large-consumer meter is "just a bigger version" of a small-consumer meter — the indirect metering setup with CTs is fundamentally different in design from a direct meter.
Intervening in or replacing CTs/metering equipment oneself without involving the metering-responsible party — this falls outside the authority of the installation owner and can jeopardise metering accuracy/legality.
Failing to have the existing CT setup checked, in the case of own generation (CHP, battery storage), for whether it still correctly measures the changed (bidirectional) current profile.