In the world of electrical safety (such as IEC 62368-1 or IEC 60601-1), a Single Fault Condition (SFC) is a specific scenario where one—and only one—component or safety measure in the system fails. Common Examples of Single Faults When a safety lab tests a power supply, they intentionally "break" it in specific ways to see what happens. Common single faults include:
Open Protective Earth: The ground wire is disconnected. The device must still be safe to touch (no high "leakage current").
Interruption of a Supply Conductor: One of the main power lines (Line or Neutral) is cut.
Short Circuit of Insulation: A single layer of "Basic Insulation" is bypassed or fails.
Component Failure: A single capacitor, diode, or transistor is intentionally short-circuited or opened.
Blocked Cooling: A fan is intentionally stalled, or air vents are covered. The device must shut down safely without melting or catching fire.
State | Description | Description |
Normal Conditon (NC) | Everything is working as designed. | Zero risk to the user. |
Single Fault Condition (SFC) | One safety barrier or component has failed. | Still zero risk to the user (though the device might stop working). |
Safety labs generally do not test for "Double Faults" (two independent things breaking at exactly the same time), as the statistical probability is considered low enough to be acceptable.