| Q. |
What is a Hipot? |
| A. |
A Hipot (which is an acronym for high potential) is a testing instrument used to verify the integrity
of an electrical product’s insulation.
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| Q. |
What is a Hipot test? |
| A. |
This test, also known as the Dielectric Withstand test, is used to stress the insulation of a product
far beyond what it would encounter during normal operation. High voltage is applied from the mains-input
lines to the chassis of the product for a specified length of time to check the integrity of the insulation
by monitoring resulting leakage current. The hipot test is a 100% production line test and can be performed
using either an AC or a DC voltage.
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| Q. |
What is a Dielectric Voltage Withstand test? |
| A. |
A Dielectric Voltage Withstand test is another name for a Hipot test. The two terms are used interchangeably
in the industry.
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| Q. |
How do I determine the proper Hipot test voltage for my application? |
| A. |
The best way to determine this is to check the specification you must comply with for your tests.
Typically the “rule of thumb” for an AC test voltage is (2 * operating voltage + 1,000 volts). So if your
products operating voltage is 115 volts AC the answer would be (2 * 115) + 1,000 = 1,230 volts. Test voltages
may vary depending upon the classification of the product.
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| Q. |
How do I determine the proper Hipot current trip point for my application? |
| A. |
Unlike the case of test voltage, there is no leakage “rule of thumb” for the current trip setting.
Sometimes acceptable leakage levels are determined by testing a sampling of products that can provide
acceptable ranges. Some UL specifications call for a leakage adjustment to be made with a 120kΩ resistor
across the Hipot test leads. Contact your local safety agency office or our Technical Services department
for more information.
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| Q. |
What is the difference between leakage, breakdown and arcing? |
| A. |
Leakage is the current that is leaking through product’s insulation system. Breakdown is a disruptive discharge
through or across the insulation system resulting in a sudden large increase in current through the insulation.
Arcing occurs when the insulation system fails in a given area of a DUT and the voltage flashes over from one conductive
surface to the other.
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| Q. |
How do I determine if I need to test with an AC or DC voltage? |
| A. |
The type of test voltage you must use during a test may or may not be specified by the safety agency’s
standard you are using. If it is not specified, you may usually use either an AC or DC output voltage. However,
there are different considerations to take into account when using a DC voltage. Contact your local safety agency
office or our Technical Services department for more information.
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| Q. |
What is the difference between a grounded return and a floating return? |
| A. |
Usually these terms refer to the return side of the Hipot tester. Some Hipot testers have the return side
of the instrument referenced to ground while others have a lifted or floating return. Floating the return
bypasses stray leakage to ground making leakage readings more accurate. If you ground your DUT during a test
you cannot use a Hipot with a floating return as the leakage current through the DUT will be bypassed around
the current meter and the failure detection circuits. You must un-ground the DUT or the testing line before
testing, or you will not be able to get any current meter reading.
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| Q. |
Should the power switch of my product be turned on during a Hipot test? |
| A. |
Yes. In order to be sure current flows throughout the entire insulation system, all power switches must
be set to the on position.
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| Q. |
What is the VA rating of a Hipot? |
| |
The VA or (Volt-Amp) rating is the power output of the instrument and is determined by multiplying the maximum
output voltage by the maximum current. For example 5,000 volts * 100 milliamps = 500VA.
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| Q. |
Is the AC output of a Hipot indicated in RMS? |
| A. |
AC output can be monitored in peak, peak-to-peak or RMS voltages. Since most DUT’s operate on RMS
voltages during normal operation the Hipot test should also be measured in RMS.
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| Q. |
Is there a difference between DC and AC Hipot tests? |
| A. |
Yes. The difference becomes most noticeable when testing highly capacitive DUT’s. Since AC
voltages cannot charge a capacitive load, reactive current flows instantly and remains consistent regardless
of the time the voltage is applied. DC voltages will charge the capacitance of the DUT so you may see an inrush
of current upon initial application of the voltage but gradually the readings will dissipate as the DUT becomes
charged. As a result of this phenomenon, current readings will usually differ between an AC and DC Hipot test.
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| Q. |
How can I determine if my Hipot is functioning properly and how often should I check it? |
| A. |
Verifying the failure detection circuitry of electrical safety testers is required by safety agencies.
This test is normally required to be performed at the start of each shift to validate that the instrument
is functioning correctly. Some Hipot testers must be verified using an external load bank, while others
can be verified through a Verification feature.
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| Q. |
What is GFI protection and why is it used? |
| A. |
GFI stands for Ground Fault Interrupter. A GFI detector has a sensing circuit that will disable the
tester’s high voltage output when excessive leakage current (> 500 µA) flows to ground. This is a safety
feature added to many Hipot testers to protect the test operator from accidental electric shock.
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