Generator sizing guide UAE
Choose the right generator size for the way your site actually runs.
A load total on a spreadsheet is only the beginning. This guide explains the information we need to check motor starting, load steps, duty and site conditions before selecting a generator.
Step 1
Build a load schedule that reflects operation
Record what runs, when it runs and how it starts. Connected load alone normally overstates simultaneous demand but can still miss a short, severe motor-starting or UPS step.
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| Record for each load | Why it matters |
|---|---|
| Running kW or kVA and power factor | Establishes the steady electrical demand seen by the generator |
| Starting method and starting current | Direct-on-line motors can create a much larger transient than their running load |
| Operating sequence | Shows which loads are simultaneous and identifies the largest accepted step |
| Load type | Motors, UPS systems, drives, welders and resistive loads behave differently |
| Essential or shed-able status | Allows staged loading and load shedding instead of unnecessary oversizing |
-
Running kW or kVA and power factor
- Why it matters
- Establishes the steady electrical demand seen by the generator
-
Starting method and starting current
- Why it matters
- Direct-on-line motors can create a much larger transient than their running load
-
Operating sequence
- Why it matters
- Shows which loads are simultaneous and identifies the largest accepted step
-
Load type
- Why it matters
- Motors, UPS systems, drives, welders and resistive loads behave differently
-
Essential or shed-able status
- Why it matters
- Allows staged loading and load shedding instead of unnecessary oversizing
Step 2
Check motor starting, UPS systems and the largest load step
A generator can carry the steady load and still produce an unacceptable voltage or frequency dip when a large motor starts. Starting method, motor inertia, acceptable acceleration time and the loads already online all affect the result.
UPS systems, variable-speed drives and other rectifier loads can introduce harmonics and a high crest factor. The alternator and control response should be reviewed against the equipment input characteristics rather than treated as a simple unity-power-factor load.
- Identify the largest motor and its starting method
- State the maximum acceptable voltage and frequency dip
- Define staged loading and automatic load-shedding logic
- Provide UPS input data, including harmonic or rectifier information
- Allow for future loads only when the expansion is credible and quantified
- Review alternator excitation and subtransient performance for demanding steps
Step 3
Match the rating to duty and UAE site conditions
Prime and standby ratings are not interchangeable labels. Expected operating hours, average load, overload requirement and maintenance strategy must match the rating definition offered for the selected model.
Standby duty
Define outage duration, annual operating expectation, transfer sequence, exercise regime and required redundancy.
Prime duty
Provide expected annual hours, average load, peak profile, maintenance windows and fuel strategy.
Ambient and altitude
State the maximum design temperature and installation elevation so engine and alternator derating can be checked.
Installation package
Confirm indoor or outdoor location, ventilation, exhaust, acoustic limit, dust, footprint and access.
Step 4
Send a sizing brief we can work from
- 01
Load data
Send the load schedule, single-line diagram, largest step, starting methods and operating sequence.
- 02
Electrical data
Confirm voltage, phase, frequency, earthing arrangement and the downstream switchgear interface.
- 03
Operating duty
State prime or standby use, expected hours, redundancy basis and required autonomy.
- 04
Site data
Provide ambient, altitude, indoor or outdoor arrangement, noise criterion, dust and access constraints.
- 05
Acceptance data
List approved makes, applicable specification, test requirements, documentation and required delivery date.
Frequently asked questions
Common questions
Can’t find what you need? Send us your requirement and our team will help.
Can generator kVA be selected from total connected load?
Not reliably. Connected load is one input, but simultaneous demand, power factor, motor starting, UPS or nonlinear loads, operating sequence, duty and site derating can materially change the required generator.
Should a diesel generator be oversized for future expansion?
A defined future load can be included, but excessive oversizing can create prolonged low-load operation and unnecessary capital cost. Quantify the expansion, timing and operating sequence before adding capacity.
How does UAE heat affect generator sizing?
High ambient temperature can reduce engine, alternator and cooling-system capability. The maximum design ambient and enclosure or plant-room airflow must be checked against the selected manufacturer data.
What information does Patsons need to confirm a generator size?
Provide the load schedule, largest motor or load step, duty, voltage, frequency, site ambient, altitude, package type, acoustic limit, fuel autonomy, redundancy and project specification.