Hipot testers are an essential tool for testing the current and insulation resistance of electronic equipment.
The test is performed by sending current through the insulation of the device under testing (DUT).
Hipot testing may determine the rate of loss of current—called leakage current—in the insulation and determine how durable and reliable the insulation is at protecting users.
What is A Hipot Test?
Hipot—high potential—testing refers to the practice of checking and verifying electronics to make sure they can withstand high voltage spikes and resist leakage current.
Hipot testers are used to test the capacity of electrical insulation to handle its load and ensure devices won’t cause electric shock during normal use.
The test is also known as dielectric withstand testing, in which the test device is subjected to the high voltage and duration that would be produced by a fault.
The most important tests a hipot tester can do are low-resistance measurements and low-resistance/high-current outputs.
Electrical equipment manufacturers use hipot testing to test the maximum safe voltage level that the equipment can operate under.
It’s also used as a risk assessment tool to help manufacturers and testing laboratories to ensure that the electrical and electronic equipment they are using is safe.
Why is HIPOT Testing Important?
Electrical safety testing is essential to ensure electrical equipment is safe to use and will not cause injury to the user.
Electrical safety testing is an integral part of the manufacturing process and it’s carried out to ensure that the electrical device is safe.
If the electrical equipment creates a shock hazard, it may not be allowed to enter the market and will not be sold.
It’s important to make sure that a given product you use or sell is completely safe and meets the relevant safety standards.
If you don’t test your product properly, it may create a potential risk to your customers or employees.
Routine inspection and maintenance of sensitive electronic devices is a requirement for meeting NRTL certification standards.
Performing periodic inspection and calibration of hipot voltage and current test machines is also required to maintain your certification.
Hipot Test Standard
OSHA’s NRTL program details the hipot testing specifications for each category of electronics you must inspect on a regular basis.
Here are a few of the wide-reaching standards you need to meet regardless of what sort of tests you’re running:
1. 120,000-Ohm Minimum Tester Tolerance
Your hipot tester for conducting the dielectric withstand test must be adjusted to a sensitivity setting such that when a resistor of 120,000 ohms is connected across the output, the tester does not indicate unacceptable performance for any output voltage above or below the specified test voltage range.
2. No Breakdowns
Some standards don’t use a fixed value limit; they simply state that breakdown shall not occur.
This means the circuit needs a certain amount of resistance between any two points, but that amount can change a good bit.
Dielectric withstand test devices are far more flexible than they used to be determining the limits in a given circuit.
You can find a detailed table of different high-voltage device categories and their hipot test voltage limits in this guide to electrical safety testing.
Hipot Test Procedure
Hipot tests are done by connecting one side of the supply to safety ground and the other side is connected to the conductor being tested.
If you have more than two leads, ground all but one and connect only the last cable to isolate the electrical insulation on the test lead.
Once you’ve applied voltage to the test circuit, wait a short period of time and check the current.
If the insulation is sufficient, voltages between the hot wire and ground line will be close, and the total current flow will be low with a near-zero level of capacitive power discharge.
If the insulation is worn or defective, applying high voltage to one side of the device test cables will cause the circuit to exceed the hipot tester current limit.
AC and DC hipot methods are applied slightly differently, and since you’ll work with both types of circuits, you must know
AC Hipot Testing
With an AC hipot test, you don’t need to set a ramp time.
AC testing also has the advantages of checking both voltage polarities and not needing to discharge the test device or cable after testing is complete.
AC hipot testing is more reliable but carries more operator risk than a DC test.
They’re typically performed with higher-voltage and higher-current devices and cause more stress on the DUT, but since they more accurately detect DUT breakdown and insulation failures, more regulation agencies endorse AC testing for than DC.
DC Hipot Testing
DC testing can be done with lower-power devices making it safer for the operator and putting the test equipment under less stress.
It also may be easier to get accurate measurements on high-capacitance devices using DC hipot testing.
Unlike AC tests, DC hipot gets real-value measurement of leakage currents with nearly zero stress on the DUT’s conductors.
However, it’s harder to get an accurate measurement since DC circuits require you to set a ramp time for testing, and the time varies among devices.
This means that even though DC tester is safer to perform and more affordable than AC testing, it’s not nearly as reliable for checking voltages and currents accurately.
As a result, far fewer safety agencies accept DC testing methods for device safety certification.