In short. A warehouse can have the lights on and still be stopped, because dispatch depends on the warehouse management system, the network, scanners, dock equipment and security as much as on illumination. Backup power should carry the digital and safety loads first, the handling equipment needed for the operating model next, and treat forklift charging as deferrable. Size from the shift profile, not the connected load, and plan cable routes around vehicle movement.
What actually stops when a warehouse loses power
Logistics sites in the corridors around Hyderabad, Medchal, Shamshabad and along the Vijayawada highway are built around flow: goods in, put away, pick, pack, dispatch. An outage interrupts the flow in ways that are not obvious from the electrical drawing. The warehouse management system server or its link to the cloud drops, so no pick lists are issued. Wireless access points go dark, so handheld scanners cannot confirm anything. Dock levellers and shutter doors stop mid-travel, so vehicles cannot be loaded. Conveyors and sorters stop with parcels on them. Barcode and label printers reset. CCTV and access control fail at the moment when the site is most exposed. A modern fulfilment centre with automated storage or a sorter is more fragile still, because its control system must be re-homed before anything moves.
The engineering consequence is that the backup scope must be built from the operating model rather than from a list of electrical equipment. Ask what must keep running to receive, pick and dispatch during an outage of the expected duration, and what can wait.
Classify the loads by what they do for dispatch
| Function | Typical equipment | Consequence of loss | Priority on generator |
|---|---|---|---|
| Life safety | Fire pumps, sprinkler controls, emergency lighting, smoke vents, PA | Statutory and safety exposure | First, by design |
| Digital control | WMS servers, network switches, access points, scanners, printers | No transactions, no dispatch | UPS, then generator |
| Security | CCTV, access control, gate barriers, perimeter lighting | Theft and audit exposure | Early |
| Dock operations | Levellers, shutter doors, dock lights | Vehicles cannot load or unload | Early, sequenced |
| Material flow | Conveyors, sorters, vertical lifts, cranes | Throughput loss | Depends on operating model |
| Task lighting | High-bay LED in active aisles | Picking stops | Active zones only |
| MHE charging | Forklift and reach-truck chargers | Deferrable for hours | Shed, restore later |
| Temperature-controlled zones | Chillers, cold rooms | Product loss | See cold-storage guidance |
| Offices and canteen | Air conditioning, pantry | Inconvenience | Last or excluded |
Where the site includes cold rooms or a frozen zone, the refrigeration plant changes the sizing entirely and has its own rules, which are covered on cold-storage power. The general method of ranking loads is on critical-load classification.
Sizing from the shift profile
Warehouse demand moves through the day. Inbound peaks in the morning, picking and packing through the shift, dispatch in the evening, and the forklift fleet charging overnight. The generator should be sized for the loads that will run together during backup operation, which is rarely the site’s metered maximum demand, because charging and offices are shed. Measure or log the demand for a week if a meter is available, then subtract the deferrable and excluded loads and add the starting demand of the largest motor in the retained set, usually a conveyor drive, a sorter or a chiller compressor.
S_gen = (P_retained / PF) + S_start
In this expression S_gen is the indicative generator kVA, P_retained is the running kW of the retained loads, PF is their power factor and S_start is the transient apparent power of the largest motor start once the base load is on the bus. For a 20,000 square metre dry warehouse with 110 kW of retained lighting, IT, security, docks and conveyors at 0.85 PF, and a 22 kW conveyor drive started direct-on-line, S_gen is about 130 kVA plus roughly 170 kVA of transient, pointing to a 200 to 250 kVA set depending on the acceptable voltage dip (illustrative). If the same site insisted on charging 40 forklifts during the outage, the figure would double, which is why charging is normally deferred. The full method is on generator sizing.
Battery charging as a managed load
Forklift chargers are large, numerous and tolerant of delay. A fleet of lead-acid trucks charges for eight hours overnight; lithium fleets use opportunity charging through the shift. In both cases a load management scheme that blocks chargers on loss of mains and releases them in groups once the generator has capacity avoids a much larger set. If the generator is a paralleled plant, chargers become the lowest priority step in the controller’s shedding table; see load management.
Fire load and generator location
Warehouses carry a high fire load in packaging, pallets, plastics and stored goods, and the fire authority’s requirements for the sprinkler and hydrant pumps often set a minimum generator capability regardless of commercial preference. The generator itself and its fuel storage should be located so that they are not inside the storage hazard, with the CPCB stack height, ventilation and acoustic requirements met, and with vehicle protection where trucks reverse nearby. The room or enclosure needs maintenance access that does not require closing a dock. Installation considerations are set out on installation planning.
Temporary and rental power on a working site
Many logistics sites take a rental set for an HT shutdown, a transformer change or a peak season, and the problems are rarely electrical. The set must be placed where trucks do not reverse into it, cable routes must cross yards and docks without becoming trip or crush hazards, and the connection point must be agreed with whoever controls the main switchboard. Define cable routes and ramps on the actual site plan, agree who operates the changeover and who refuels, and confirm the site’s operating hours so that testing does not coincide with the dispatch peak. Practical points are on rental and temporary power and rental cables and distribution.
Common mistakes
- Backing up lighting and leaving the network cabinet on the mains. The building is lit and nobody can pick, pack or dispatch.
- Including the forklift charging room in the generator scope. The set is sized for a load that could have waited eight hours.
- Starting conveyors, sorters and dock equipment together after transfer. The combined inrush trips the generator and the control system must be re-homed.
- Placing the rental set and cables in the truck apron. A reversing vehicle damages a cable or the set in the first week.
- Assuming the fire pump is on the generator because it is in the building. Fire pump supply arrangements are statutory and must be designed, not assumed.
What to send us
Send a site plan showing docks, yard and the main switchboard, a load list grouped by function with motor ratings for conveyors, sorters and any refrigeration, the IT and network loads, the number and type of charging points, and your metered demand data if available. Tell us whether the requirement is a permanent standby set, a rental for a shutdown or season, or both. Send your warehouse power requirement.
Questions engineers ask
What size generator does a warehouse need?
It depends on the retained loads, not the floor area. A dry warehouse that retains safety, IT, security, docks and some conveyors often needs 150 to 300 kVA (illustrative), while adding refrigeration or full charging can multiply that. Measure, decide what is shed, then size.
Should forklift chargers be on the generator?
Normally no, or only as the lowest priority with automatic blocking. Charging is deferrable for hours, and including it forces a much larger set that runs lightly loaded the rest of the time.
Do WMS servers and network equipment need a UPS as well as a generator?
Yes. The transfer gap of 10 to 15 seconds would drop servers, switches and access points, and the restart would take far longer than the outage. A small UPS bridges the gap and the generator carries the load afterwards.
How should a rental generator be placed on a busy logistics site?
Outside the vehicle apron, with barriers, with cable routes that avoid dock traffic or are protected by ramps, and within reach of a connection point agreed with the switchboard owner. Agree refuelling, operation and test times around the dispatch schedule.
Can a warehouse generator also serve a future cold room?
Only if it was sized for the compressor starting and running load. Refrigeration changes the scope substantially, so plan for a second set or a larger room now if cold storage is on the horizon.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.