In short. A load inventory is a structured list of every electrical load a generator may have to carry, with its kW, power factor, voltage, starting method and operating role. It separates connected load from simultaneous demand, marks which loads must run during an outage, and identifies loads that restart together. Done properly, it is the single most valuable input to generator sizing, because every later calculation inherits its accuracy.
Why a list of nameplates is not an inventory
Adding up nameplate ratings gives connected load, and connected load is almost never what a generator carries. A textile unit near Hyderabad with 800 kW of installed equipment may run between 250 kW and 600 kW depending on the shift, and may never exceed 650 kW. Sizing to 800 kW buys a set that spends its life below 50 percent load. The opposite error is just as common: a cold store with a modest average demand restarts all its compressors within a minute of transfer, and that restart, not the average, decides the set.
An inventory therefore records more than a number. It records how each load behaves, when it runs, how it starts, and what happens to it when the supply fails and returns. That information lets the sizing engineer find the simultaneous demand and the worst transient, and it gives the next reviewer a traceable basis for the decision.
Fields to capture for each load
| Field | Why it matters | Typical source |
|---|---|---|
| Equipment name and location | Identifies the load for later verification and shedding decisions | Plant layout, panel schedules |
| Quantity | Several identical units may start together or in sequence | Site walk |
| Rated kW and kVA | Basis of running demand | Nameplate, manufacturer data |
| Voltage and phases | Single-phase loads create unbalance on a three-phase set | Nameplate |
| Power factor and efficiency | Converts mechanical kW to electrical kVA for motors | Nameplate, measurement |
| Starting method and starting current | Decides the starting kVA and voltage dip | Starter panel, motor data sheet |
| Duty and operating hours | Separates continuous, intermittent and seasonal loads | Operations staff |
| Outage role | Must run, may run, or shed during generator operation | Owner decision |
| Restart behaviour | Automatic restart, manual restart or sequenced by a controller | Control scheme |
For motors, note whether the nameplate kW is mechanical output. Electrical input is higher by the efficiency, and apparent power is higher again by the power factor. A 37 kW motor at 0.92 efficiency and 0.85 power factor draws about 47 kVA at full load (illustrative). The kW to kVA guide explains the conversion.
Connected load, demand and diversity
Three quantities must be kept apart. Connected load is the sum of ratings. Maximum demand is the highest sustained load actually drawn, usually averaged over 15 or 30 minutes as the DISCOM meter does. The largest step is the biggest single increase the set may see at one moment, which lasts seconds and is invisible in demand records.
Diversity is the ratio between simultaneous demand and connected load, and it must be justified, not assumed. Acceptable justification includes metered demand from the electricity bill or a data logger, process knowledge that shows which machines never run together, or interlocks that prevent simultaneous operation. Applying a generic 0.7 across a plant without understanding the process hides risk: an HVAC plant may have a diversity near 1.0 on a hot afternoon, while a machine shop may be below 0.5. The connected load and maximum demand guide goes further into measurement.
Loads that behave differently on generator
A supply failure changes how loads behave, and the inventory should record it. After the transfer switch closes onto the generator, every load with a held-in contactor has dropped out and every load with a latched or automatic restart comes back. Compressors, pumps, chillers and air handlers with automatic restart return within seconds of each other unless a restart delay or sequencing is built into the controls. This group restart is often the hardest event the set faces, and it is far larger than the normal running load of the same equipment.
UPS systems are the other special case. On generator, the UPS carries its load and simultaneously recharges its battery, so its input demand is above its output rating until the battery recovers. Its input current is also non-linear, which the harmonics guide covers. Variable-speed drives, induction heaters and welding machines also deserve a note, because their current waveforms and intermittent duty affect the alternator differently from a plain resistive load.
Marking the outage role
Every load should carry one of three tags: must run on generator, may run if capacity allows, or shed during an outage. The must-run group sets the minimum size; the shed group becomes the load shedding list. This decision belongs to the owner or process manager, not the electrical contractor, and recording who made it avoids disputes at commissioning.
A worked inventory (illustrative)
A pharmaceutical warehouse in the Genome Valley area lists 320 kW of connected load: 110 kW of HVAC with six air handlers and two chillers, 60 kW of cold room compressors, 40 kW of lighting, 30 kW of IT through a UPS, 50 kW of material handling and 30 kW of miscellaneous sockets. The owner decides that HVAC, cold rooms, IT and emergency lighting must run on generator, and material handling and general sockets are shed. The must-run connected load is 240 kW. Logged demand for that group peaks at 185 kW at 0.86 power factor, or 215 kVA. The hardest event is the two chillers restarting within thirty seconds of transfer, each with a 22 kW compressor starting direct-on-line. By adding a staggered restart of sixty seconds between chillers in the BMS, the starting event drops to one compressor at a time, and a 250 kVA set becomes viable where a 320 kVA set would otherwise have been proposed. The inventory, not the generator catalogue, produced that saving.
Keeping the inventory alive
Record the date, the source of each figure and the person responsible. Keep planned equipment on a separate sheet so that future load is visible but not confused with present demand. Revise the inventory when machines are added, when shift patterns change, or when a rental set is mobilised, because rental installations are often overloaded gradually as extra equipment is plugged in over the weeks. A dated inventory also lets a later reviewer understand why the original set was chosen when expansion or replacement comes up.
Related photographs and videos
Common mistakes
- Recording motor nameplate kW as electrical demand, which understates kVA by 15 to 25 percent and leaves the alternator short on every motor-heavy site.
- Applying one diversity factor across all loads without process knowledge, which either oversizes the set or lets a real coincident peak overload it.
- Ignoring automatic restarts after transfer, so the set carries the steady load easily and trips on the group restart it was never sized for.
- Leaving the must-run decision to the installer, which produces a set sized for everything and a shedding scheme nobody agreed to.
What to send us
Send your load list in any form you have, even a panel schedule or a photograph of the main distribution board, together with the last few electricity bills showing recorded maximum demand, nameplate photographs of the largest motors and any UPS, and a note of which loads must keep running when the grid fails. If you are not sure how the HVAC or compressors restart, tell us the make of the controller and we will ask the right questions. Send your application engineering enquiry.
Questions engineers ask
Can I use the electricity bill instead of a load inventory?
The bill gives recorded maximum demand, which is a good anchor for running load because it includes real diversity. It does not show which loads must run during an outage, how motors start or what restarts together, so use it alongside an inventory rather than instead of one.
What diversity factor should I use for generator sizing?
There is no safe universal figure. Derive it from metered demand or from process knowledge of which machines run together. If neither is available, measure for a week with a data logger before committing to a generator size.
How do I handle single-phase loads in a three-phase inventory?
Record the phase each single-phase load is connected to and total them per phase. A generator should normally see no more than about 10 percent unbalance between phases, and heavy single-phase loads such as welding sets may need rebalancing at the distribution board.
Should future loads be included?
Yes, but on a separate line with a date and an owner, and with their starting characteristics stated. A vague allowance inflates the set; a defined future load can be designed for, or deferred to a second set.
Who should decide which loads are essential?
The business or process owner, with input from safety and engineering. It is a decision about consequence and cost, and it should be recorded in the inventory with the approver’s name.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.