The DG Set Is Installed and Tested. The Inspectorate Still Has Not Cleared It.

A diesel generator arrives as a packaged product. It is craned into place, connected, load-tested, and everyone treats it as commissioned. Then someone asks whether the electrical inspectorate has cleared it, and the answer is usually that nobody filed anything.

Where a DG installation falls within the inspectorate's scope — which it commonly does, particularly when synchronised or connected through a changeover to the main supply — it is an electrical installation requiring approval before energisation, not equipment you simply buy.

What the inspectorate is actually looking at

Very little of it is the generator itself, which arrives with its own type certification. The scrutiny is on how it has been integrated:

• The single-line diagram — how the DG connects to the distribution, where the changeover sits, and how backfeed to the grid is prevented. This is the document that decides most outcomes.
• Protection and its settings — the protective devices on the DG side, and whether they discriminate correctly against upstream and downstream devices. A schedule of actual settings, not a catalogue extract.
• Earthing — the neutral earthing arrangement for the generator, earth electrode design and measured earth resistance, evidenced rather than asserted.
• Clearances and access — physical space around the set and its panel for safe operation and maintenance.
• Cabling — sizing and routing between the DG and the panel, sized for both current and voltage drop.

Why files stall

The pattern is consistent: files stall on missing evidence rather than on bad engineering. The installation is frequently fine; the submission does not prove it.

The sequencing trap

DG approval is often left until the plant is otherwise ready, on the assumption it is a formality attached to a purchased product. It then sits on the critical path at the worst moment — a finished facility that cannot legally energise, carrying full capital cost and no output.

The related trap is a DG bought and positioned before the electrical design is settled, leaving the changeover, protection and cable route to be worked out around a machine that is already bolted down. Where a synchronising arrangement is involved, that constrains the design considerably. We covered why a second engine is not automatically redundancy in DG synchronisation and parallel redundancy.

Where to start

Establish whether your installation is in scope before assuming either way — triggers vary by state and by rating. Our CEIG readiness checker gives an indicative read on applicability and how close your file is to inspection-ready, and the full process is in the CEIG approval guide. Sizing is a separate question — the DG sizing calculator covers that. Confirm current requirements with your state inspectorate.

What we do differently

Under CEIG approval consultancy we prepare the drawings and calculations the inspectorate actually reviews — SLD with protection settings, earthing design with measured values, discrimination study — then file, answer the queries and attend the inspection, so energisation is not the thing holding up a finished plant.