When reviewing the datasheet for a power supply or electronic instrument, you will find a specification for Withstand Voltage, sometimes referred to as Dielectric Withstand Voltage. This is a critical parameter that guarantees the safety and reliability of the product. It serves as a key indicator that the product is protected against risks such as electric shock and fire, ensuring it can be used with confidence.
The Fundamentals of Withstand Voltage
In simple terms, withstand voltage is the maximum voltage that a product's insulation can endure for a specified time without breaking down.
Electrical components are "insulated" to prevent current from flowing where it shouldn't, such as the instrument's chassis or between the input and output circuits. However, if a sufficiently high voltage is applied, this insulation can reach its limit and fail, allowing current to pass through. This phenomenon is known as Electrical Breakdown. The withstand voltage specification guarantees that electrical breakdown will not occur up to a certain voltage level.
Example on a Specification Sheet
On a product catalog or datasheet, the withstand voltage is typically listed as follows:
- Input to Output: 1500 VAC for 1 minute
- This indicates that the insulation between the input and output terminals is guaranteed to withstand 1500 volts AC for one minute without failure.
- Input to Chassis (Case): 1500 VAC for 1 minute
- This specifies the insulation performance between the input terminal and the metal case, which a user may touch.
A related specification is Voltage to Ground. This indicates the maximum voltage at which the output terminal can be safely operated relative to earth ground, which is particularly important when connecting outputs in series to achieve a higher voltage.
Key Differences: Clarifying Common Terminology
Several tests and terms related to insulation performance can be easily confused. Understanding their distinct purposes is essential.
Withstand Voltage Test vs. Insulation Resistance Test
While both of these tests are indispensable for ensuring product safety, they have different objectives.
| Item | Insulation Resistance Test | Withstand Voltage (Hi-Pot) Test |
|---|---|---|
| Purpose | To confirm that the insulation quality is sufficient (i.e., that it resists current leakage). | To verify that the insulation does not break down when subjected to a specified abnormal voltage. |
| Analogy | A "health check" for the insulation. | A "stress test" for the insulation. |
| Applied Voltage | A relatively low DC voltage (e.g., 500 VDC, 1000 VDC). | A very high AC or DC voltage (e.g., 1500 VAC). |
| Measurement | Resistance value (Unit: MΩ). A higher value indicates better performance. | Pass/Fail. The test confirms that no breakdown or abnormal discharge occurs within the specified time. |
In essence, the insulation resistance test checks the quality of the insulation, while the withstand voltage test proves its strength.
Technical Deep Dive: Isolation Voltage vs. Withstand Voltage
When reviewing technical documents and datasheets from global manufacturers, you may encounter the terms "Isolation Voltage" and "Withstand Voltage." While they appear similar, they often have distinct meanings, especially in the context of international safety standards.
Withstand Voltage
This metric indicates the insulation's ability to endure a temporary voltage stress.
- Meaning: The maximum voltage that can be applied for a short, specified duration (typically one minute) without causing dielectric breakdown.
- Application: Used in production-line testing and safety certification tests (hipot tests) to confirm that a product has a sufficient safety margin. It is commonly specified as an AC RMS value.
- Concept: A value that guarantees the product's insulation strength during a short-term stress test.
Isolation Voltage
This metric indicates the insulation's performance during long-term, continuous operation.
- Meaning: The maximum voltage that can be continuously applied across the isolation barrier during the equipment's normal operation over its entire service life.
- Application: Closely related to the Working Voltage, it serves as the basis for the insulation design for the product's rated operation.
- Concept: A value that ensures safety during routine, daily use.
It is worth noting that in some contexts, "Isolation Voltage" may be used more broadly to encompass all voltage-related requirements for isolation, including the withstand voltage.
Summary: The Difference Between the Two Voltages
| Term | Meaning | Application & Purpose |
|---|---|---|
| Withstand Voltage | The voltage that can be tolerated for a short time (e.g., 1 minute). | Production testing, safety certification. Confirms the safety margin against temporary stress. |
| Isolation Voltage | The maximum voltage that can be continuously applied without issue. | Insulation design for rated operation. Ensures long-term safety and reliability. |
Simply put, Withstand Voltage is a test value that proves momentary durability against a potential fault or transient voltage. In contrast, Isolation Voltage (or Working Voltage) is a rated value that indicates continuous safety during normal use. Understanding this distinction is crucial for accurately interpreting the specifications of any high-performance instrument, from a high voltage power supply or bidirectional power supply to an AC power source.
- Related words:
-
- Insulation Resistance Test
- Withstand Voltage (Hi-Pot)
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