Views: 0 Author: Zhejiang Shengxian Electric Technology Co., Ltd Publish Time: 2026-07-21 Origin: Zhejiang Shengxian Electric Technology Co., Ltd
The maximum current a switchgear can carry continuously under normal operating conditions without overheating or damage. This is the cabinet's everyday workload — a measure of its thermal capacity under continuous service.
The current that spikes far beyond normal levels when a fault occurs. Short-circuit current isn't something you "choose" for the cabinet — it's an external shock imposed by the grid's structure that the cabinet has to survive.
In short: rated current is how much the cabinet does day-to-day; short-circuit current is how much impact it has to withstand when something goes wrong on the network.
Parameter | Meaning | What it measures |
|---|---|---|
Rated short-time withstand current (Ik) | The RMS value of short-circuit current the switchgear can withstand while closed, for a specified short duration (standard: 4s or 2s) | Thermal stability — can it survive the heat without burning out |
Rated peak withstand current (Ip) | The peak value of the first major half-cycle of the short-time withstand current, roughly 2.5× the short-time withstand current | Dynamic (mechanical) stability — can it survive the electromagnetic force without deforming |
Rated short-circuit duration (tk) | The time period over which the switchgear must carry the short-time withstand current, standard value 2s or 4s | Determines how long the busbar and structure must be designed to hold |
Example: a switchgear rated "31.5kA/4s" means it can withstand an RMS short-circuit current of 31.5kA for 4 seconds after a fault without damage (thermal stability), while its instantaneous peak current tolerance is roughly 31.5kA × 2.5 ≈ 78.75kA (dynamic stability).
This is where buyers often slip up:
Rated current determines whether the conductor cross-section and heat dissipation design can handle daily load
Short-time withstand current determines whether the busbar cross-section and structural strength can handle the instant of a fault
If you only check whether the rated current is sufficient without verifying that the short-circuit withstand rating matches the local grid's short-circuit capacity, the cabinet may burn out or deform when a fault actually occurs — with potential safety risks.
Confirm the project load and calculate normal operating current to select the right rated current class (e.g. 630A, 1250A, 2000A)
Check the system short-circuit capacity at the connection point with the local utility or grid design authority
Compare against the cabinet's short-time withstand current rating, ensuring it meets or exceeds the actual grid short-circuit level with a safety margin
Verify the peak withstand current meets the dynamic stability requirement (usually specified alongside by the supplier, no separate calculation needed)
Confirm the short-circuit duration rating (2s vs 4s) matches local standard requirements (this varies slightly by country)
Scenario | Parameter to check |
|---|---|
How much load can the cabinet carry day-to-day | Rated current |
Can the cabinet survive a grid short-circuit fault | Rated short-time withstand current + rated peak withstand current |
How long can the cabinet hold up during a fault | Rated short-circuit duration |
Selection shouldn't stop at "is the rated current enough" — short-circuit withstand capability is the parameter that actually determines a switchgear's safety, which is why properly labeled cabinet nameplates list rated current and short-time withstand current separately.
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