In short. Retail backup power needs a clear answer to one question: whose loads are actually on the standby bus. A mall combines landlord services, tenant supplies and shared infrastructure under different contracts, so the generator scope must be drawn as a boundary on the single-line diagram, not left in a lease clause. Life safety and public movement come first, tenant essential supply is metered and billed, escalators and HVAC are restored in steps, and decorative loads are shed.
Three owners of load under one roof
A shopping centre in Hyderabad or Visakhapatnam is electrically three facilities. The landlord owns the common areas: lifts, escalators, car park ventilation, fire systems, central air conditioning, common lighting, water and sewage pumps, security and the building management system. Tenants own what is behind their meters, from a jewellery store’s lighting to a food court kitchen to a multiplex with projectors and its own UPS. Anchor tenants often negotiate dedicated feeders and a guaranteed generator allocation. Each has different interruption tolerance and different ideas about who pays for backup, and an outage exposes any ambiguity immediately.
The engineering task is to turn those commercial relationships into an electrical boundary: which feeders are on the essential bus, how much each tenant is allocated during generator operation, how that allocation is enforced, and how the units are metered. Without this, the mall discovers during its first long outage that the standby plant is carrying loads nobody intended and dropping ones that were promised.
Landlord load classes and the restoration order
| Group | Loads | Restoration | Notes |
|---|---|---|---|
| Life safety | Fire pumps, smoke extraction, staircase pressurisation, emergency lighting, PA, fire lifts | Immediately on transfer | Statutory; defined by the fire design |
| Public movement | Lifts, selected escalators, atrium and corridor lighting, car park lighting and CO ventilation | Within the first minute, staged | Escalators restarted in groups, not together |
| Operations | BMS, CCTV, access control, parking barriers, water and sewage pumps, security office | Early | UPS for BMS and CCTV recorders |
| Tenant essential | Allocated kVA per tenant for lighting, POS and refrigeration | After landlord essentials | Metered for DG billing |
| Food court and anchor kitchens | Cold rooms, exhaust hoods, selected cooking equipment | Sequenced | Food safety and fire interlocks |
| Comfort cooling | Chillers, AHUs, tenant air conditioning | Stepped by load management or excluded | Largest decision in the plan |
| Shed | Façade and decorative lighting, digital signage, fountains, non-essential escalators | Not restored on generator | Blocked by control, not by goodwill |
Comfort cooling is the same hard choice it is in any commercial building, with the added point that a mall without air conditioning empties quickly, so many operators retain part of the chiller plant through a paralleled generator plant with load management. The ranking method is explained on critical-load classification, and the stepping logic on load management.
Peak restoration is the sizing event
A mall’s running load during an outage can be carried by a plant sized sensibly for it. What breaks the plant is the first minute after transfer, when escalators, lifts, car park fans, pumps and chillers all try to start together. Escalators and lifts have high inrush; chillers are the largest single step; car park fans are large motors often started direct-on-line. The arithmetic is simple, but it must be applied to the restoration sequence rather than to the equipment list.
S_plant = P_landlord-essential / PF + Σ S_tenant-allocation + S_largest-step
In this expression S_plant is the indicative standby plant kVA, P_landlord-essential is the running kW of the landlord’s life-safety, movement and operations groups, Σ S_tenant-allocation is the sum of the tenant allocations in kVA, PF is the power factor and S_largest-step is the transient kVA of the largest start after the base load is connected. For a mid-sized centre with 450 kW of landlord essential load, 600 kVA of total tenant allocation, PF of 0.85 and a 55 kW car park fan starting direct-on-line, S_plant is roughly 1,130 kVA plus about 430 kVA of transient, which suggests two 750 kVA sets in parallel with comfort cooling excluded, or three or four sets once chillers are added (illustrative). A paralleled plant also allows one set to be serviced during trading hours; see generator paralleling and N+1 generator plants.
Escalators and lifts
Escalators should restart in groups controlled by the BMS or the load management controller, with a delay between groups. Lifts should be released floor by floor by the lift controller once the generator is stable. Both regenerate energy on descent, which a diesel plant cannot absorb; the lift and escalator drives must have braking resistors active in generator mode or the plant’s reverse-power protection will operate. Inrush figures for these drives are discussed on starting kVA.
Tenant allocation, enforcement and metering
A tenant allocation that exists only in the lease is unenforceable. Each tenant feeder on the essential bus should have a protective device or a load-limiting relay set to the allocation, so that a tenant who switches on more than agreed trips their own supply rather than the mall’s plant. DG units are typically metered by dual-tariff or event-logging meters that record consumption while the generator is running, and billed at a declared rate that recovers fuel, maintenance and capital; the metering and control arrangement should be part of the electrical design and the fit-out guide, not a dispute after the first bill. Distribution design points are on cables, busbars and distribution.
Working in an occupied retail environment
Testing, maintenance and electrical work in a mall affect many businesses at once. Define the distribution boundaries so that isolation for work on the essential bus does not take down tenants unnecessarily, agree work windows in the hours after closing, publish a monthly transfer test time, and name a single contact on the landlord side who authorises isolation and restoration. The generator proposal itself should state its coverage in plain terms, listing the groups and tenants it supports and the ones it does not, so that store managers do not assume protection that was never designed. Testing practice is described on load-bank testing.
Common mistakes
- Sizing the plant for the mall’s maximum demand. The owner buys and maintains two or three times the capacity the restoration plan needs.
- Promising tenant allocations without a load-limiting device. One tenant’s extra air conditioning overloads the plant and every tenant loses supply.
- Letting the BMS restart all escalators and lifts together after transfer. The combined inrush trips the plant and shoppers are stranded twice.
- Leaving signage, façade lighting and fountains on the essential bus. Decorative load is carried while a food court cold room is shed.
- Never running a sequenced live test because trading cannot be disturbed. The restoration logic is first exercised during a real outage on a festival weekend.
What to send us
Send the mall’s single-line diagram with the essential bus marked, a load list of landlord services with motor ratings and starter types for lifts, escalators, fans, pumps and chillers, the tenant allocation schedule in kVA, the existing or proposed DG metering arrangement, and the trading hours and work windows available for testing. For an existing plant, include nameplate photographs and the controller and synchronising panel details. Send your mall power requirement.
Questions engineers ask
How much generator capacity does a shopping mall need?
Mid-sized centres commonly run standby plants of 1,500 to 3,000 kVA in two or more paralleled sets, and large malls far more (illustrative). The figure follows from the landlord essential load, the sum of tenant allocations and the largest motor start, with comfort cooling the biggest variable.
How are tenants charged for generator power?
Tenant feeders on the essential bus carry meters that record units during generator operation, and the landlord bills those units at a declared DG rate. A load-limiting device set to the lease allocation prevents a tenant drawing more than agreed.
Why do escalators trip the generator after a transfer?
Because they all start together, and because escalator and lift drives regenerate on the down direction. Group restarts with delays and braking resistors active in generator mode solve both problems.
Should the chillers be on the standby plant?
Partially, in most malls, through load management that adds chillers after essential loads are stable and sheds them first when capacity is short. Full chiller backup is a commercial decision that typically doubles the plant size.
How often should a mall generator plant be tested?
A monthly transfer test on real load at a published early-morning time, an annual load-bank test of each set, and a sequenced restoration test at least once a year so that the BMS and load management logic is proven, not assumed.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.