Switchgear Sizing: Load Current and Fault Duty Need Separate Checks
Prepare a selection brief that distinguishes normal operation from fault requirements.
A switchgear assembly can meet the normal load-current requirement and still need further checks before it is suitable for the installation.
Normal current, fault duty and the conditions attached to equipment ratings answer different questions. Keep them separate in the selection brief rather than describing the whole requirement with one ampere value.
Distinguish the ratingsContinuous current and short-time withstand current are not interchangeable.
The load current tells you what the switchgear must carry during normal operation.
Fault duty tells you what the equipment may need to withstand for a defined short duration during an abnormal condition.
A switchgear proposal should therefore be reviewed across multiple requirements rather than judged from one current figure alone.
Gather the project basisPrepare the available project data before starting the sizing review:
system voltage
frequency
load schedule
normal operating current
available fault-study information
short-circuit level
protection requirements
installation conditions
future expansion requirements
Identify whether the information represents the existing network or a proposed system change.
If the fault study or protection basis is incomplete, mark the selection as preliminary rather than filling the gap with a convenient catalogue value.
Compare proposals consistentlyAsk each supplier to identify:
the proposed switchgear assembly
applicable voltage class
continuous-current rating
short-time withstand rating
duration attached to that rating
applicable configuration
supporting technical documentation
Keep any deviations explicit.
Avoid comparing an isolated component rating with a complete assembly rating as though they are automatically equivalent.
The supplier should confirm which ratings apply to the offered configuration.
Begin the Ruhify reviewOpen the Ruhify 11 kV MV AIS Switchgear page with your load schedule and available fault-study data ready.
Check the displayed voltage class, equipment scope and available calculator inputs before applying the workflow to your project.
A useful preliminary sequence is:
System voltage → Load current → Fault duty → Protection basis → Installation conditions → Preliminary selection
You can also use the Ruhify AI Agent to interact with available technical and product knowledge while reviewing the application.
Ruhify AI Search can help users locate relevant switchgear information, engineering content and sizing tools without manually navigating through multiple pages.
Explore the broader platform at Ruhify.
Keep the selection traceableThe useful result is not simply a switchgear ampere rating.
It is a documented selection basis showing:
Normal load → Fault requirement → Equipment rating → Assumptions → Supplier confirmation → Open questions
That record makes it easier for another engineer to understand why a particular switchgear arrangement was considered suitable.
Explore the Ruhify switchgear page with your load schedule and study data available.
This is a preliminary sizing workflow. Final switchgear selection requires validated system studies, applicable standards, manufacturer data and qualified electrical engineering review.