Load shedding should follow an agreed understanding of which functions must remain available and which can be deferred. The responsible facility team should define these priorities and the consequences of removing each load. A power rating alone does not establish its operational importance.
Connect shedding to available capacity
The control strategy needs to consider the generating capacity actually available and the conditions that trigger action. Restoration is a separate decision: reconnecting several loads can create a new demand event. Define both removal and reconnection behaviour within the approved operating philosophy.
Triggers can be based on project logic
- generator loss
- available capacity
- frequency condition
- system state
Restoration
Load shedding is not losing loads accidentally. It is preserving the highest-priority loads deliberately.
Define restoration as well as shedding
For each load group, establish what may be disconnected, the condition for restoration and any restart constraints. Returning all loads simultaneously can create a new transient demand. The sequence needs to follow the approved operating priorities and available capacity.
Keep operational authority clear
Settings and priorities should be documented and changed through an authorised process. Verify the sequence against the agreed scenarios and record the result. Operators need to understand the supported configuration and what to do when facility demand or process priorities change.
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Related guidance
Engineering intent
Load Shedding should be evaluated as part of the complete power system rather than as an isolated catalogue item. Operating duty, connected load, interfaces, protection, controls, installation conditions, testing requirements and lifecycle consequences determine whether the arrangement is appropriate.
Engineering considerations
The required reserve depends on the actual plant and reliability philosophy. “What happens if the largest operating generator trips?” Sometimes preserving the parallel plant requires controlling the load. Load shedding can therefore be a deliberate resilience function. An engineered system may use frequency-related information as part of a load-management strategy. If reserve becomes inadequate, the plant can take an appropriate programmed action. This can be more intelligent than waiting for every generator to reach an emergency condition. Shedding load is only one half of the control problem. The system should also determine when loads can safely return. Restoration may need to be staged to avoid:
Selection and design considerations
Removing capacity without confirming reserve can create instability when the next load step arrives. Additional unit brought online when demand or reserve requirement justifies it. Do not use fixed lead/lag logic without considering actual operating duty. Duty rotation can balance operating hours across generators. A generator due for service, in alarm, low on fuel or unsuitable for the current load should not be blindly selected. When available capacity becomes insufficient, the system may shed lower-priority loads. Load shedding should not be viewed automatically as failure. In a properly engineered system, selective load shedding can prevent total blackout. After generators are online, loads should not always reconnect simultaneously. This protects the generator plant from excessive step load.
Integration and protection considerations
A correctly sized generator does not compensate for unsafe temporary distribution. Mobile generators may sometimes be connected temporarily to existing facilities. The transfer architecture should prevent unsafe source interaction. Mobile Power Should Protect the Right Loads — Not Automatically Every Load During contingency or project operation, available generator capacity may be limited. A temporary system does not always need to reproduce the facility’s entire normal electrical demand. It needs to support the defined operating objective. Connecting every load simultaneously can create a large step demand. The final steady-state demand may be acceptable even though simultaneous restart would not be. Intentional load shedding can improve reliability when generating capacity becomes constrained.
Testing, commissioning and verification
If load shedding forms part of the design, commissioning should verify that lower-priority loads are removed according to the intended logic. Do not assume load shedding works because it exists on a drawing. Where required by the project, commissioning may include black-start or dead-bus logic. Such tests require explicit planning and safe procedure. Commissioning may need to verify how the system responds after a generator trip or abnormal event. Where permitted and safe, utility-failure simulation can verify the automatic standby sequence. It should not create unnecessary risk to live operations. The end of the event matters as much as the start. Emergency stop functions may need verification where applicable. Do not perform emergency stop testing without an approved procedure and safe conditions.
Operating and lifecycle considerations
A building can contain many loads with different consequences. An automatic generator system should understand the defined emergency operating requirement. Not every load necessarily needs to be connected immediately—or at all—during generator operation. This can reduce a severe instantaneous load step. After a utility outage, multiple motors may simultaneously request restart. The generator may be large enough for the final running demand but unable to accept all starting transients simultaneously. If available generating capacity becomes inadequate, selected systems can deliberately remove lower-priority loads. Properly engineered, it can be a system-preservation function. While supplying the facility, the system can monitor relevant conditions. Not every abnormal condition should necessarily create the same response.
Direct answer
Load shedding should follow an agreed understanding of which functions must remain available and which can be deferred. The responsible facility team should define these priorities and the consequences of removing each load.
The practical decision for Load Shedding should be based on verified load, equipment, interface and site information. Where equipment-specific data, regulatory applicability or a project study is required, this guidance does not replace that verification.