Choosing a G100 export-limitation scheme

What a CLS is

A Customer Limitation Scheme (ENA EREC G100) is equipment that holds the net current at the connection point within a declared ceiling — a Maximum Export Limit (MEL) for generation, a Maximum Import Limit (MIL) for demand. It works on the net flow: the house can generate far more than the limit as long as the balance leaving the premises stays under it, with the scheme throttling the inverters when it wouldn’t.

Why bother? Because the DNO plans its network around what can flow at the connection point, not what is bolted to the wall — and G99’s SGI procedures reward a capped export with a lighter process for a bigger installation:

• SGI-2 — up to just under 32 A of installed generation per phase (each unit ≤ 16 A), with a scheme limiting export to ≤ 16 A.
• SGI-3 — up to just under 60 A per phase (each unit ≤ 32 A), with a scheme limiting export to ≤ 32 A — waived entirely when the aggregate is already ≤ 32 A.

One thing a scheme never does is turn G99 into G98: the G98/G99 boundary is Registered Capacity only (see the registered-capacity guide). The scheme decides which G99 procedure, not whether G99.

The choice: inverter-integrated or a stand-alone device

• Inverter-integrated — the proposed inverters themselves are the CLS, using their built-in limitation function with a CT at the connection point. No extra hardware — but every proposed inverter must be registered on the ENA Type Test Register as a Fully Type Tested G100 CLS (the register answers yes/no on every entry). The claim is printed: G100 Form A lists those inverters’ register references as the CLS, under the customer’s signature, so CLRD refuses an inverter-integrated scheme on any proposed inverter the register doesn’t back — and the picker shows a CLS chip so you can see it before choosing.
• A stand-alone device — a separate ENA-registered limiter (the register’s “Stand-alone G100 Device” category) that holds the connection point within the limit by itself, monitoring the supply at the connection point — no integration with the inverters, and no reliance on their own limitation functions. The device’s own register reference is what Form A declares, and CLRD prints it on the form and labels the limiter box on the single-line diagram with it. A stand-alone device is the route when the inverters aren’t CLS-registered, when existing units are part of the picture (an existing inverter is never the new CLS), or when the same device should also hold an import limit — one device can carry both directions, declared as a shared export/import limiter.

Fail-safe by design

G100’s type testing is mostly about what happens when things go wrong, which is why the register flag matters more than a datasheet claim:

• Normal operation — the scheme modulates generation so the net export stays within the MEL.
• Excursion — a temporary breach must be pulled back within 1 minute (3 minutes for slow-acting devices).
• Failure — if a component or its communications fail, the controlled devices must trip or fall to a safe power level within 10 seconds. The scheme fails safe, or it isn’t a scheme.

What the DNO sees

• G100 Form A rides the application: the CLS’s register reference(s), the MEL per phase, and the customer’s signature.
• G100 Form C rides the post-install pack: the CLS installation and commissioning tests, confirming the scheme does what Form A declared. Domestic type-tested schemes are commissioned unwitnessed — the DNO doesn’t attend; the paperwork is the assurance.
• The approval may come back lower. A DNO can grant less export than was applied for (zero is a valid answer). CLRD records the granted figure with the approval, and the post-install pack states the limit the scheme was actually commissioned to, while the application keeps what it asked for.

In CLRD

Declare the scheme in the wizard’s Export Limitation section — inverter-integrated, or a stand-alone device picked from the register with its reference frozen onto the job. CLRD enforces the CLS register check on inverter-integrated schemes, applies the SGI-3 waiver automatically, routes the G100 forms onto the right packs, and draws the limiter (with its reference and limit) on the single-line diagram. An import scheme is declared alongside in the same section — the same stand-alone device or its own — and adds the same Form A / Form C pair wherever the export scheme hasn’t already.