Withstand Voltage

Withstand Voltage (also known as Dielectric Withstand Voltage or Hi-Pot) is a critical specification that guarantees the safety and reliability of power supplies and electronic instruments. It indicates the maximum voltage capability of the insulation barrier, ensuring protection against electric shock and fire hazards.

Fundamentals of Withstand Voltage

Withstand voltage defines the maximum voltage that an insulation barrier can endure for a specified duration without breaking down.

Insulation prevents unwanted current flow between circuits, such as between the AC input and the output, or between internal components and the chassis. If the applied voltage exceeds the insulation's limit, Electrical Breakdown occurs, allowing current to pass through. The withstand voltage specification guarantees that the product has been tested to verify it does not fail below a specific voltage level.

Interpreting the Specification

On product datasheets, withstand voltage is typically specified as a test condition:

Input to Output: 1500 VAC for 1 minute: Guarantees that the insulation between the input and output terminals can withstand 1500 volts AC for one minute without failure.
Input to Chassis: 1500 VAC for 1 minute: Guarantees the insulation performance between the input terminals and the metal enclosure (user-accessible parts).

A related parameter is Voltage to Ground (or Maximum Floating Voltage). This specifies the maximum voltage at which the output terminals can be safely operated relative to earth ground. This is crucial when connecting power supplies in series or floating the output.

Withstand Voltage Test vs. Insulation Resistance Test

While both tests evaluate insulation, they serve different purposes in ensuring product safety.

Feature	Insulation Resistance Test	Withstand Voltage (Hi-Pot) Test
Purpose	Checks insulation quality (detection of degradation or moisture).	Verifies insulation strength (stress test against breakdown).
Analogy	A "Health Check"	A "Stress Test"
Applied Voltage	Lower DC voltage (e.g., 500 VDC).	High AC or DC voltage (e.g., 1.5 kVAC or higher).
Measurement	Resistance (MΩ). Higher is better.	Leakage current or Pass/Fail (No breakdown).

Withstand Voltage vs. Working Voltage

It is important to distinguish between the testing voltage and the continuous operating voltage. In some technical contexts, the term "Isolation Voltage" is used, but its meaning can vary. To ensure safety, engineers must clarify the difference between temporary stress limits and continuous ratings.

Withstand Voltage (Test Voltage)

Definition: The maximum voltage applied for a short duration (typically 1 minute) during safety testing.
Purpose: Confirms safety margins and manufacturing quality.
Key Concept: Represents temporary durability against transient spikes or faults. It is not a rating for continuous use.

Working Voltage (Continuous Isolation Rating)

Definition: The maximum voltage that can be continuously applied across the isolation barrier during normal operation.
Purpose: Defines the safe operating limit for the product's lifespan.
Key Concept: Represents continuous safety. This value is typically much lower than the withstand voltage.

Note: In general electronic specifications, "Isolation Voltage" often refers to the Withstand Voltage (test value) rather than the Working Voltage. Always verify whether a specification refers to a "1-minute test" or "continuous operation" before system integration.

Summary

Term	Definition	Application
Withstand Voltage	Short-term stress limit (e.g., 1 minute).	Production testing and safety certification (Hi-Pot).
Working Voltage	Continuous operating limit.	System design and normal operation.

Understanding the distinction between Withstand Voltage (momentary test) and Working Voltage (continuous use) is essential for selecting the correct power supply and ensuring long-term system reliability.

Related Terms:

Insulation Resistance Test
Withstand Voltage (Hi-Pot)
Dielectric Strength

Related Terms