What is a Hi-pot test and how does it work

What is a Hi-pot test and why Hi-pot test is needed

A hi-pot test a test which is conducted to check the isolation, The hi-pot test is done to make sure that there is no current flow from one point to another, so the hi-pot test is considered as the opposite of the continuity test. Hi-pot is the abbreviation for high voltage test. Mostly the hi-pot test is conducted by applying a high voltage between the conductors which is isolated and the flow of current is checked usually there won’t be much current flow, if the current flow is high then the points are not well isolated. By doing the hi-pot test we can ensure that the isolation is properly done or not. Hi-pot test can be also called a dielectric withstand test the strength of the insulation can be checked by this. The strength of the insulation can be checked by applying a high voltage to the chassis of the device and by measures the leakage current which flows through its insulation. Mostly this test is done by applying higher voltage than the product usually operates so if this test is cleared then this device can run under normal operating conditions.

Electric tester and its use


What is the purpose of Hi-pot test and why high voltage test is required

Hi-pot test is done to make sure that there is good isolation between the parts of a circuit. If the electrical circuits have good isolation then the quality will increase. Hi-pot test is capable to find nicked or crushed insulation, stray wire strands or braided shielding, conductive or corrosive contaminants around the conductors. These problems could cause the failure of the device.

How does a Hi-pot test work

During Hi-pot testing one side is connected to the ground and the other one will be connected to the conductor which is tested. The conductor can be connected at two places they are high voltage or ground. If more than two contacts are needed to be Hi-pot tested, then we must connect one contact to high voltage and all the other contact to the ground, by doing this we can ensure that all the contacts are isolated from each other. If we apply a high voltage between the conductors that are separated by the proper insulation, then there will be a flow of very small current and there won’t be any breakdown of insulation.

What are the types of Hi-pot test

There are three types of Hi-pot test they are

  • Dielectric breakdown test
  • Dielectric withstanding test
  • Insulation resistance test

What is a dielectric breakdown test

A dielectric breakdown test is done to know how much voltage can be applied between the wires before the insulation fails. Voltage is increased until the current increases suddenly. By doing this test we would be able to know the highest voltage that the cable can stand. Dielectric breakdown test is used for product design and qualification stages, the maximum voltage of the design can be achieved by this.

What is a dielectric withstand test

By doing dielectric withstand the test we could know if the cable can withstand a required voltage for a required time. Dielectric withstand test is needed for every cable which is produced this test is conducted at about seventy percent of the typical breakdown voltage. By this test we can ensure the safety, this test has many advantages like it is sensitive to arc and corona so it can detect terminal spacing problems, over-mold problems…

What is Insulation resistance testing

This test is conducted to check if the resistance of the insulation is high enough. This test is done by applying the voltage and current measurements. Insulation resistance can be calculated by using ohm’s law. This test is done for every cable, mostly this test is done at 300 to 500 Vdc with 100 to 500 Mega-ohms resistance. By doing this test in each cable will help to detect the contamination changes in the manufacturing process.

Is Hi-pot testing dangerous

During the Hi-pot test, we could be at risk, we can decrease the risk by using a tester. To reduce the risk of electrical shock we must make sure that the hi-pot equipment follows certain guidelines.

  • The total charge that we receive in a shock must not exceed 45 uC
  • Hi-pot energy must not exceed 350 mJ
  • Current must not exceed 5 mA peak
  • Fault current must not stay longer than 10 mS
  • Avoid touching cable during hi-pot testing
  • We must remove the cable only after completing the hi-pot test
  • Use insulation gloves

What is the difference between megger and hi-pot

Megger is used to measure the insulation resistance, but the hi-pot testing can determine the excessive leakage current that flows through the insulation of the product.

What is the test voltage for Hi-pot testing

Hi-pot test can be done by using either AC or DC voltage, both the AC and DC hi-pot test has certain advantages and disadvantages according to the product which is being tested

What are the advantages of AC hi-pot test

  • Due to the polarity change slow ramping of the test voltage is not needed
  • After AC test there is no need to discharge the DUT
  • In AC testing the insulation will be stressed at both polarities


What are the disadvantages of AC hi-pot test

  • AC hi-pot testers are costlier and bigger than the DC tester
  • Because of their bigger size they are not suitable for field testing

What are the advantages of DC hi-pot test

  • DC test can be done at the very low current level, so power can be saved and the operator would be safe
  • We could get the leakage current measurement very accurately by the representation of the real current
  • Certain circuit components such as diodes, capacitor, etc has only DC testing option

What are the disadvantages of DC hi-pot test

  • DC test will cause space charging at the weak points of the insulation
  • DC test can’t change test polarity, and no partial discharge can be initiated
  • In order to provide accurate test results the cable that is to be tested must be at ambient temperature.
  • DC hi-pot test must be started with test voltage that must be higher than eighty percent of the cables rated AC RMS phase to phase voltage.