Complete GeneratorInstallation

Every downstream size starts from the generator's full-load current (FLC), derived from its kVA rating and the system voltage. The cable, the breaker, the changeover and the earth are all sized from this current, with margins for continuous operation (125%) and for the real installation conditions (heat, grouping, burial) that derate a cable's capacity. Our AutoSmart sizer above does this instantly; the formula below is what it applies.

The automatic transfer switch (ATS / changeover) is the heart of a standby installation: it switches the load between the grid and the generator, break-before-make, and it must be rated for the full load current with the right number of poles (3- or 4-pole, the 4th switching the neutral where the earthing scheme requires it). Sized too small, it overheats; chosen without the right transition type (open vs closed), it either drops the load briefly or requires utility agreement to parallel.

The cable is sized by two tests, and the larger wins: it must carry the design current (ampacity after derating), and it must keep the volt-drop over the run within limits (typically ≤2.5% so the load sees good voltage). A long run between a remote generator and the building can force a larger cable purely on volt-drop — which is exactly why the sizer asks for the cable length, not just the rating.

A generator is rated in kVA but does real work in kW, linked by the power factor (typically 0.8 for the set). A site full of motors at a poor power factor draws more current than its kW suggests, so the installation — cable, ATS, breaker — is sized on the kVA/current, not the kW. Where the load's power factor is poor, power-factor correction at the main board reduces the current the whole installation must carry and can let a smaller set and smaller cables do the job.

For any meaningful autonomy, the set needs an external (bulk or day) fuel tank sized to the run-time required — built bunded (a containment volume to catch a leak), vented and protected against theft. The sizer estimates the tank from the fuel burn and your target autonomy hours.

The exhaust must be sized so back-pressure stays within the engine maker's limit (an undersized pipe chokes the engine and overheats it), fitted with a residential or industrial silencer to meet the site's noise target, and routed with proper supports, a condensate drain and safe termination away from intakes and people. The generator cage / canopy protects the set and attenuates noise, and it sits on a reinforced concrete plinth raised ~150 mm above ground, sized to the set with anti-vibration mounts between machine and base. The sizer gives indicative canopy and plinth dimensions for your rating.