DG Set Installation Guide: kVA Sizing, CPCB IV+, Earthing & AMF

Size a DG set by adding up the running load you want to back up in kW, dividing by the power factor (usually 0.8) to get kVA, and then adding headroom for motor starting and future growth. For example, 24 kW of running load at 0.8 power factor needs about 30 kVA before any margin.

Starting current is where most undersized generators fail. Motors, pumps, lifts, compressors and air conditioners draw several times their running current for a few seconds when they start — a direct-on-line motor can pull roughly 6–8 times its rated current. If several large motors start together, the generator's voltage dips, contactors drop out and the set can stall. Staggering motor starts, or using soft starters and star-delta starters, lets you choose a smaller set.

Aim for the generator to run at roughly 60–80% of its rating under normal backup load. A heavily oversized set spends its life lightly loaded, which causes incomplete combustion, carbon build-up and "wet stacking" (unburnt fuel in the exhaust), while an undersized set overheats and struggles on every start.

The right rating depends on your actual load list, but these ranges give a realistic starting point before a site survey.

Almost every new DG set up to 800 kW sold in India today must comply with the CPCB IV+ emission norms, which came into force in July 2023 and replaced the older CPCB II standard. CPCB IV+ sets use cleaner engine technology with electronic controls and exhaust after-treatment, so they emit significantly less particulate matter and NOx.

Gensets are also expected to come in an acoustic enclosure (canopy) that meets the CPCB noise limits. A silent canopy houses the engine, alternator, control panel and usually the fuel tank in a weatherproof, sound-insulated box, which makes it suitable for residential areas, commercial complexes and hospitals.

When buying, check the set's type-approval and conformity documentation for CPCB IV+ and noise compliance. Because CPCB IV+ engines depend on electronics and after-treatment, using the right fuel quality and following the service schedule matters more than it did with older sets.

Place the DG on a level, reinforced concrete plinth in a well-ventilated spot with clear access on all sides for servicing, as close to the main panel as practical to keep cable runs short. The plinth should be slightly larger than the set's footprint, raised above the surrounding floor so rainwater doesn't collect under it, and cured properly before the set is placed.

Anti-vibration mounts (AVMs) between the base frame and the plinth stop vibration travelling into the building structure. Flexible connections on the exhaust and fuel lines, and flexible cable glands, prevent vibration from cracking pipes and loosening terminals over time. For rooftop or terrace installations, a structural engineer should confirm the slab can carry the set's weight and vibration.

The exhaust must be routed away from windows, doors, air intakes and occupied areas, with the discharge point high enough to disperse fumes safely. CPCB guidelines set a minimum stack height for DG sets based on the building height and the generator rating, so the exhaust pipe on a society or commercial set often has to be carried well above the roofline. Long exhaust runs need the right pipe diameter, minimal bends and support brackets to avoid back pressure, which cuts power and raises engine temperature.

Enclosed DG rooms need enough fresh-air inlet and hot-air outlet area to keep the engine cool and stop it re-breathing its own hot air. Canopy sets placed outdoors still need clearance around the air intake and radiator discharge.

The fuel tank should be sized for the backup duration you need, fitted with a level indicator and drain, and kept clean. Large external fuel storage is subject to petroleum and fire safety rules, so it is usually easier to plan runtime around the set's built-in tank plus a safe top-up arrangement.

The changeover decides how your building switches between grid and generator, and it must make it impossible for the DG to back-feed the grid. CEA safety regulations require a generator connected to an installation to be interlocked so it can never energise the supply company's lines — which protects linemen working on the network.

A DG set needs its own dedicated earthing, and common Indian practice is two separate earth pits: one for the generator neutral and one for the body. Larger sets often get additional pits for each so that one failed pit or connection doesn't leave the set unprotected. The neutral earth provides the reference point for the generator's star point, while the body earth carries fault current from the frame, canopy and control panel so a fault trips the protection instead of making the enclosure live.

Keeping neutral and body earths separate at the pits (and bonded as the system design requires) keeps neutral-to-earth voltage low, which protects sensitive electronics and inverters running on DG power. Earth pits for DGs are usually pipe, plate or chemical earthing, tested after installation and at least once a year.

Power cables from the DG to the changeover and main panel must be sized for the full-load current of the set, the length of the run and the installation method, with proper glands and lugs. The DG output should have its own breaker (MCCB or ACB, depending on rating) with overload and short-circuit protection coordinated with the downstream breakers.

Commissioning should cover a no-load run, a step-load test, a check that voltage and frequency hold steady as load is applied and removed, a test of every safety shutdown (low oil pressure, high temperature, over-speed), changeover or AMF operation, and earth-resistance readings. A handover should include these readings and a clear starting and shutdown procedure for whoever operates the set.

A standby DG fails most often because it sat idle — so regular test runs under load matter as much as oil changes. Follow the manufacturer's schedule for oil, oil filter, fuel filter, air filter and coolant, based on running hours and time, whichever comes first.

Electrons handles DG set installation end to end for homes, societies, shops, hospitals and industry across Zirakpur, Panchkula, Chandigarh and Mohali. We visit the site, prepare a load list and size the set in kVA, plan the plinth, anti-vibration mounting and exhaust route, wire the manual changeover, ATS or AMF panel, install dedicated DG earth pits and power cabling, and test and commission the set with you. After handover, we can look after servicing through an AMC, with 24/7 emergency call-outs if the set lets you down.