Generators for Apartments and Gated Communities: Lifts, Pumps, Common Areas and Flat Backup

In short. An apartment generator usually backs up lifts, water pumps, common lighting, security and the fire system’s support loads — and, in many communities, a limited supply to each flat. The sizing questions are how many lifts may run at once, how pumps start, and how much each flat is allowed to draw on backup. Without a per-flat limit, a few air-conditioners can overload a set sized for lights and fans.

Who this page is for: For apartment associations, facility managers and builders: decide what the community generator should back up, how much each flat can draw, and how to keep the set reliable and fair to all residents.

What the community set usually carries

Worked example: 120-flat block (hypothetical)

Hypothetical figures to show the method.

Running load ≈ 87 kW. At 0.8 PF and no more than 80 % loading: 87 ÷ 0.8 ÷ 0.8 ≈ 136 kVA, before checking pump and lift starting. A 160 kVA set may suit; if flats were allowed 1 kW each, the flat load alone would roughly double. The per-flat limit is the biggest decision the association makes.

Association backup-policy sheet

Placement, noise and safety

• Exhaust discharged well away from windows, balconies and air intakes
• Acoustic canopy and placement that respects neighbouring blocks
• Fuel stored safely, with spill containment and no ignition sources nearby
• Earthing designed and tested; access restricted to trained staff

When the usual assumptions fail

• “Only lights and fans in flats.” Without a limiter, residents will connect ACs. Enforce it electrically.
• Lift regeneration. A set that trips when a full lift descends at night is usually seeing regenerated energy, not overload. The lift and generator must be set up together.
• Light-load running. Large sets that carry only common lighting at night run very lightly; schedule meaningful-load exercise.

Questions for the association’s managing committee

• What per-flat backup limit is fair, and how will it be enforced?
• How many lifts must run during outages, and do their drives suit generator supply?
• Who runs the monthly test, and who records hours and fuel?
• How is generator cost shared — by flat, by backup meter, or in maintenance charges?
• Is the set’s canopy and exhaust acceptable to residents nearest it?

Checking motor starting: lifts and pumps

Running load decides whether the set can carry the community; starting load decides whether it can get there. A motor draws several times its running current while it accelerates, at a poor power factor, and the generator’s voltage dips while it does. If the dip is deep enough, lift drives drop out, contactors chatter and lights flicker in every flat.

Compare the largest single starting step with the alternator’s motor-starting capability on the data sheet, which is stated as starting kVA at a given voltage dip. Then make sure no two large starts can happen together: a timer that holds pump restarts for a minute or so after changeover, while lifts settle, costs very little and removes the worst case. Our motor starting page explains the dip calculation in depth.

Diversity: why 120 flats do not draw 120 limits

Diversity describes how far the group’s actual maximum demand falls below the sum of every flat’s limit; the 60 % figure in the 120-flat example above means about 60 % of that sum is drawn at the evening peak. Not every flat uses its full backup allowance at the same instant. In the evening, when lights, fans, televisions and refrigerators are all on, diversity is lowest — that is the hour to size for. At 2 am it is very high and the community draw may fall to a small fraction of the evening figure. Measure both: one evening reading and one late-night reading from the set’s meter tell the association more than any estimate.

Choosing a flat-backup scheme

How the association shares backup decides fairness, generator size and the number of complaints the committee receives. All of these schemes must be designed and installed by a licensed electrical contractor, with the mains and generator sources interlocked so they can never be connected together.

Residents must never connect a home generator or inverter output into the building’s common wiring or a neighbour’s supply. Back-feeding can energise cables that maintenance staff believe are dead.

The night light-load problem

A 160 kVA set carrying 15 kW of common lighting through a night outage runs at under 12 % of its rating. Diesel engines held at such light loads for long periods do not reach full working temperature; unburnt fuel and oil collect in the exhaust (wet stacking), fuel consumption per useful kW rises, and lift regeneration is more likely to trip the set because there is so little load to absorb it. Remedies, in order of effort: run the monthly test at a meaningful load rather than idling it; keep pumps scheduled to refill tanks during long night outages; arrange a periodic load-bank run if the logs show long light-load hours; and, for new projects, consider two smaller sets so that one carries the night load.

Maintenance governance across committee changes

Generator problems in apartments are as often administrative as mechanical. Managing committees change every year or two, and knowledge leaves with them. Keep a single generator file that passes to each new committee: the set’s data, service contract scope and dates, the running-hours and fuel log, test records, the flat-backup limit decision and the lift company’s confirmation that drives are set for generator supply. A simple fuel sanity check catches leakage and pilferage: a healthy diesel set at moderate-to-high load typically uses roughly 0.25–0.3 litres per kWh generated, so litres used ÷ kWh recorded should stay steady month to month.

A second worked example: the borewell pump that dimmed the towers

Illustrative case. A two-tower community has a 200 kVA set. During an outage the set is carrying 90 kW when a 15 HP (11 kW) borewell pump starts direct-on-line. Lights dip across both towers and one lift stops between floors and re-levels.

The set is not overloaded; the running figure is comfortable. The problem is a sudden 88 kVA step at low power factor on a set already carrying over half its rating (90 kW of the 200 kVA set’s 160 kW at 0.8 power factor); the resulting transient dip is enough to trip this lift drive’s under-voltage protection. Fitting a soft starter halves the step, and a restart timer keeps the pump from starting within the first minute after changeover. Buying a larger generator would have been the expensive and less effective answer.

Common mistakes

• Sizing from the total sanctioned load of all flats instead of measured demand with diversity.
• Forgetting the lifts’ and pumps’ starting current when choosing the set.
• Running a large set all night on common-area load alone, which causes light-load damage.
• Leaving maintenance to whoever is on duty, with no log, no AMC and no tested changeover.

What to send us

Send the number of blocks and flats, lifts (number and motor size), pumps, common-area loads, how backup is shared with flats today, the existing set’s kVA and age if any, and the typical outage pattern. Use the application engineering enquiry, or WhatsApp the details and photographs.

Related pages

• Prime Power Generators
• AMF Panels
• Generator Summer Precautions

Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer. Last updated 3 November 2026.