The most important specifications to consider when searching for hipot testers include AC and DC output voltage, AC and DC output current, resistance range, insulation limit, and test time. Output voltage can either be AC or DC. The type of test will determine what level of voltage will be supplied. For example: in hipot testing the output voltage is usually very high. Output current can either be AC or DC. The type of test will determine what level of current will be supplied. For example: in hipot testing the output current is usually very low. Testers can also measure the resistance range. The insulation limit specification determines the voltage range the insulator can withstand. Many tests performed for electrical safety have a test time requirement. This is the overall time of the test.

The testing method for hipot testers can be automatic, semi-automatic, and manual. Some test instruments are fully automated to store and perform testing from a program. They may also have the ability to perform a series of electrical safety tests. Semi-automatic is a combination of automatic and manual testing capability. Manual testing requires that an operator be present to make physical changes to the test parameters.

Displays and interfaces are also important to consider when searching for hipot testers. Display choices include analog meters, digital meters, and LED indicators. Interfaces include GPIB, RS232, printer ports, scanner ports, and printouts. Safety agency ratings that can be applied to hipot testers include CE conformity marks, CSA, IEC, IPC, TÜV Rhineland (US, C, US & C), UL listing, and VDE. Common features for hipot testers include built-in calibration, buzzer or annunciator, front panel lockout, memory or storage, multiple test setup, PLC interface, rapid cutoff, remote control, selectable output frequency, and warning indicator lights.

What makes an Operator Qualified?

NFPA 70E defines qualified persons in the following manner:

“A qualified person shall be trained and knowledgeable of the construction and operation of equipment or a specific work method, and be trained to recognize and avoid the electrical hazards that might be present with respect to that equipment or work method. Such persons shall also be familiar with the proper use of special precautionary techniques, personal protective equipment, insulating and shielding materials, and insulating tools and test
equipment.”

It is the employer’s responsibility to provide safety related work practices, maintain a safe working environment and train the employees implementing those practices. One way an employer can help ensure a safe working environment is by using electrical safety testers with safety agency listings. Recognizing this, OSHA requires that electrical instruments used in the workplace be listed by a Nationally Recognized Testing Laboratory (NRTL). There are a total of 18 NRTLs recognized by OSHA. To ensure that the hipot testing being performed is safe, and to comply with OSHA requirements, it is best to use a safety tester that is listed by one of these recognized testing labs.
The degree of training required for the operators performing the product safety test is highly dependent upon the set up of the
product safety testing workstation. Whenever possible, the workstation should be constructed so that there are no exposed energized circuits and so that it employs some positive means to protect the operator from coming in contact with the device under
test (DUT). When the electrical testing workstation does not employ positive protection, the operator must be trained to recognize and avoid the potential hazards. Figure 1 is an example of a workstation that employs automatic protection against direct contact with the DUT. The hooded enclosure is interlocked to the hipot.

The Dielectric Voltage Withstand Or Hipot Test

The dielectric voltage withstand or hipot test is a routine production line test that can be hazardous if theoperator is not aware of the potential hazards of the higher voltages that he/she is working with. The hipot test is the deliberate application of an excessive amount of voltage intended to stress the insulation of a DUT.

Here are 10 examples of the knowledge of a test operator should have as it pertains to hipot testing with exposed energized circuits:

1. A test operator should have a basic understanding of electricity, voltage, current, resistance, and how they
   relate to each other. A test operator should also understand conductors, insulators and grounding systems.
2. A test operator should have a working knowledge of the test equipment, the tests that are being
   performed, and the hazards associated with the tests, as well as the circuits that are being energized.
3. A test operator should understand the approach distances and corresponding voltages to which they may be exposed.
4. A test operator should be trained to understand the specific hazards associated with electrical energy.
   They should be trained in safetyrelated work practices and procedural requirements as necessary to provide protection from the electrical hazards associated with their respective job or task assignments. Employees should be trained to identify and understand the relationship between electrical hazards and possible injury.
5. A test operator should understand the three primary factors that determine the severity of electric shock, namely:
   A. The amount of current flowing through the body
   B. The path of the electrical current through the body
   C. The duration or length of time the person is exposed
6. A test operator should know that the human body responds to current in the following manner:
   A. 0.5 to 1 mA: perception level
   B. 5 mA: a slight shock is felt, a startle reaction is produced
   C. 6 -25 mA for women and 9 -30 mA for men: produces the inability to let go
   D. 30 – 150 mA: extreme pain, respiratory arrest, ventricular fibrillation and possible death
   E. 10 amps: cardiac arrest and severe burns can occur
7. A test operator working on or near exposed energized electrical conductors or circuit parts should be trained in methods of release of victims from contact with exposed energized conductors or circuit parts.
8. A test operator should understand that the test instrument is a variable voltage power source and the current will flow to any available ground path. A test operator should be aware that contacting the device under test (DUT) during the test can result in a dangerous shock hazard under certain conditions.
9. A test operator should understand that, if the return circuit is open during the test, then the enclosure of
   the DUT can become energized. This can occur if the return lead is open or the operator lifts the return lead from the DUT while a test is in process.
10. A test operator should be made aware of the importance of discharging a DUT. Lifting the high voltage lead from the DUT before the test is complete can leave the DUT charged. When you are performing a hipot test, you are testing the insulation between two conductors which is essentially a capacitor. This capacitor can act as a storage device and hold a charge
    even when performing an AC test. If  the circuit is opened at the peak of the applied voltage, the DUT could hold a charge, even under an AC test. When the test is allowed to finish and the voltage is reduced to zero, the charge is dissipated through the impedance of the high voltage transformer. Most DC hipot testers today employ an output shorting device to discharge the DUT, but the hipot must remain connected to the DUT throughout the test cycle.

This is just a partial listing of the knowledge required for a test operator  to be able to safely perform a hipot test. Many product safety testing workstations are set up for maximum productivity rather than safety. If the test station is not set up with positive
protection against direct contact, then a potentially hazardous situation can result. Even the placement of the test equipment can create a potential shock hazard. For instance, if the operator has to look away from the DUT to observe the test equipment, he/she could inadvertently contact an energized circuit, or a return probe could accidentally slip off resulting in an energized chassis.

Performing a hipot test on a DUT with exposed energized circuits can be much safer when a tester is used that offers the latest technology and safety features. Many testers today have multiple shut down circuits to disable high voltage. These testers use both
adjustable high limit and low limit current sense circuits. The high limit circuit will shut down the hipot within 0.5 seconds if the adjustable current threshold is exceeded. This commonly occurs when there is a breakdown of the DUT’s protective insulation.

A second sensing current is the low limit current sense circuit. During a normal hipot test, the enclosure of the DUT is at or near ground potential (see Figure 2). The low limit circuit monitors the test for a minimum current draw and will shut down the circuit if a minimum current flow through the DUT is not detected. This most often is the result of an open lead or the operator not making a good contact with the return lead (see Figure 3). In either of the above cases, the DUT chassis could become energized present a shock hazard for an operator coming in contact with the chassis.

Increasing Hipot Testing Safety

To offset this potentially dangerous situation, there have been many developments made to increase the safety of hipot testing. One example is the recent development of a GFI circuit into electrical safety testers. This provides operators with an even greater
level of protection from electrical shock. The GFI circuit reduces the risk of the operator receiving an electrical shock when testing an ungrounded DUT, and it can also protect operators who come into direct contact with the high voltage output of the electrical
safety tester. Most GFIs will shut down the high voltage if excess leakage current of 450:A is detected through the ground circuit. This is a high-speed shutdown circuit that disables the high voltage in less than 1 millisecond.

In order for the GFI circuit to properly work in electrical safety testing applications, the safety tester’s return lead needs to be ungrounded or floating. Having the return lead floating means that the case of the DUT, to which the return lead is normally
connected, must also be isolated from earth ground. If the return lead is disconnected or is open, then there is no path for the current to return to its source. If an operator were to come in contact with the DUT case, then he/she could complete the return path. The GFI is designed to eliminate this situation.

A GFI in an electrical safety tester works in the following manner. One point of measurement senses the current returning from the DUT through the return, while the other point of measure is return current combined with current coming back through earth ground. With a good DUT that is floating, these measurements should be almost identical since very little current should return through the ground connection. If there is a condition whereby the operator comes into contact with the high voltage circuit and completes a path to ground, the GFI will sense an excessive differential between these two points and shut down. However, if the DUT is grounded, all the current returns directly through the ground point thereby bypassing the other leg of the GFI. This results in a difference in measurement between these two points, causing a false GFI failure indication. If  you have to test a grounded DUT that will require the return to be grounded, then the GFI circuit must be manually disabled.

There are also some GFI circuits on the market that integrate so-called “smart” technology. In cases where the DUT is earth grounded, such devices will allow the “return ground sense” circuit to automatically disable the GFI circuit and the instrument operates in a grounded return mode of operation. This mode allows the user to perform their tests normally without the operator
having to manually change the instrument’s configuration. When test conditions change from grounded return back to a floating return, these “smart” GFIs will automatically enable themselves, allowing the tester to monitor the return condition of the
DUT itself without manipulation of the GFI circuits by the test operator.

Many testing applications are very versatile and production lines can quickly be re-configured to manufacture and test a wide range of different products. In some cases, these products might be grounded via a production roller platform, requiring the return of
the electrical safety tester to be grounded and on others the return may be floating. Smart GFIs ultimately provides the most effective safety protection since it is an active circuit monitoring the configuration of the return connection which automatically
sets itself accordingly. By eliminating the operator from the equation, such devices work as an effective safety circuit because they do not require human interaction that could invite operator error.

Other Steps Toward Safe Testing

The test operator should be trained in the care, use and inspection of any personal protective equipment and insulating tools required to do the job. The test operator should also perform a daily visual and functional verification test on the test equipment. This is done to certify that the equipment is functioning properly and to verify that the equipment will detect a fault condition. A common way of performing functional verification tests is the use of an external verification box or external resistor bank. While these verification procedures do perform their intended purpose, they also represent an extra piece of equipment that must be
hooked up to the safety tester.

In order to help satisfy this requirement, some companies like HARREXCO offer safety testers with a built-in self verification feature, since today’s safety testers contain microprocessor-controlled technology and software driven circuits that allow for verification to be built-in to the instrument. If available on your instrument, this verification test should be performed at
every shift change. Likewise, if personal protective equipment such as high voltage gloves are in use, then they must be
inspected before each use and electrically tested at a minimum of every 6 months. Any defects must be reported immediately
and the defective item must not be used.

Summary

Preventing against the risk of injury while performing hipot tests should be a primary concern of any manufacturer.

Fortunately, through the use of engineering and work practice controls, this risk can be greatly reduced. These controls should be automatically in place and enacted each time a hipot test is performed. A secondary precaution that can be taken is the use of safe and up-to-date electrical safety testers. Safety agency listed hipot testers ensure that the test equipment and workstation being used is safe. In addition, technology has been developed that enhances safe testing. GFI circuitry has greatly reduced the risk of operator shock, and maintaining functional checks and calibration schedules of the hipot tester are now being built into safety testers themselves. These developments, coupled with operator training and a proper work station set-up, have made performing electrical
safety tests much easier and safer for manufacturers.

Reference: www.conformity.com

The test applies high voltage to the product to check the insulation between the live conductors and exposed metal surfaces. For Class I equipment, the high voltage is applied between conductors and earth. For Class II equipment, the high voltage is applied between the conductors and the outer surface of the product.

Developments

Although there have been few noticeable alterations in the hipot testing requirements of most standards in recent years, many changes have been made to the technical specifications of electrical and electronic products. Such modifications have been prompted by technical standards such as the Electromagnetic Compatibility (EMC) Directive. For example, EMC considerations have required the introduction of circuit devices on the supply input to prevent emissions back into the mains.

These devices often take the form of resistive and capacitive circuits. When tested using an ac hipot test, these circuits often prove problematic because the capacitive part can induce leakage currents in excess of the capacity of the test instrument. Situations such as these have led to a substantial increase in the use of dc hipot testers that are unaffected by this capacitive effect.

The test is designed to ensure the safety of the product and to ensure that manufacturers meet legislative demands in relation to product liability and due diligence. Hipot testing, ground-bond testing, and insulation-resistance measurement are probably the three core tests for electrical safety testing.

Identification and Traceability

The hipot test can be regarded as a negative test on the basis that a good product most likely does not provide a measurable flow of leakage. With the development of modern instrumentation using microprocessor control and data-logging software, it is now possible to produce fully traceable records of testing undertaken.

Knowing why flash testing is necessary is important, but being able to prove that electrical or electronic products comply with the various standards is also vital—particularly if a subsequent failure or fault is identified.

The only effective means of demonstrating that a product has been tested properly is through sufficient documentation. The latest available testers automate the testing process on the production line and retain results in an internal memory for later download or print out. Documentation through automated hipot testing minimizes liability and provides effective proof at the end of the manufacturing process that a product is safe.

Test Conditions

Two distinct forms of testing are usually recognized: type testing and production line testing.

Type-testing levels vary according to the relevant product-specific standard. Class I equipment normally requires between 1000 and 1500 V applied for 1 minute with a trip level of up to 100 mA. Some standards specify that “no flashover shall occur,” suggesting that the trip level should be 0 mA. But, because all devices have a small amount of leakage, 0 mA is not practical. A low level of between 3 and 5 mA is usually selected. A higher level should be used if the device under test (DUT) has large capacitive leakage.

For Class II equipment, voltages are usually between 2500 and 4200 V, but with timing and trip settings similar to Class I equipment. The same criteria for the fault-trip levels are applied to both Class I and Class II products.

Production line hipot testing requires special considerations in terms of conditions such as duration and voltage levels. On the production line, the need to have faster, but equally rigorous, tests is addressed by applying 10% overvoltage, but reducing the test duration to a few seconds. Therefore, a type test with a voltage rating of 1250 V would be carried out at 1375 V on the production line, with trip levels of 5 mA. Often, the annex section of a standard advises routine testing. When a recommendation is not available, the manufacturer must apply a suitable test-voltage level to ensure that the device is safe to be offered for sale.

One note of caution is that it is possible to get an apparently satisfactory result when the equipment under test is switched off or not properly connected. It is imperative to ensure that the equipment is switched on and properly connected. Even for experienced operators, this can be a challenge. In a production line situation, such problems are greater because of the greater throughput of products. Solutions include:

• A simple continuity test, applied on live and neutral, built in to the test program prior to the flash test.

• The detection of capacitive leakage that occurs whenever an ac hipot is applied. If no leakage is detected, a warning is initiated.

• Regular fault simulation at the test connection point.

Pass-Fail Criteria. The test itself is not quantitative, and “fail” is recorded if a breakdown of insulation or a flashover between components occurs. Most testers indicate pass or fail via a warning light or sound that activates when 5 mA of leakage occurs.

Hipot and Insulation Testing. On first examination, these two tests appear very similar. However, hipot testing is designed simply to detect gaps or clearances between conductive parts and earth, pinholes in insulation, and other degradation. Insulation resistance testing is designed to provide an actual quantitative measurement of the insulation quality.

If a wire were positioned 1/2 mm from exposed metal, an insulation test—conducted in dry air—might easily provide a pass reading. A hipot test, however, is more likely to detect this situation as dangerous. Similarly, if insulation were somehow contaminated, a hipot test would produce a pass, whereas an insulation test would highlight a deficiency. For example, the normal minimum insulation resistance value for Class I appliances is 2 M(omega). With a 1500-V hipot test, the current would be 0.75 mA and would not be detected by the 5-mA trip that must accommodate the capacitive losses that occur. Obviously a dc hipot test with a leakage meter can provide insulation resistance monitoring because the capacitive component is overlooked after the initial inrush.

Test Duration. The best way to maximize productivity is to minimize the time taken to apply all of the safety and functionality tests. By using an integrated test station and enclosure connection to the DUT, only one test sequence is required. Establishing a connection is often the most time-consuming part of production line testing, so combining four or five tests at an integrated test station can significantly reduce test times.

Production Line Safety. Type tests often call for high levels of high voltages to be applied for up to 1 minute. This is not practical in production facilities. In many facilities, a 1-minute test would adversely affect productivity. The call for a 100-mA trip level can be potentially lethal. In addition, voltage levels and test procedures realistically demand a skilled operator.

Because production line hipot testing is conducted with reduced test times, it reduces the risk to operators. Effectively designed test instruments mean that the required operator skill level can be reduced, and the use of high trip levels can be protected by a key system for which only qualified operators have access.

Safe Test Areas. With the integration of electrical safety testing standards in EN 50191, specific safety conditions have been specified for all locations where electrical testing is carried out.1 For example, the use of test enclosures on the production line is advisable to maximize the safe working area around the points where flash tests are to be applied.

The type test, with its high-level leakage limits at 100 mA, is potentially lethal to the human body. Hence, type testing is carried out in a laboratory and not on a production line. The test is also only to be carried out by a skilled person who is aware of the potential hazards and who is following procedures clearly defined before any test is applied. The ideal situation is for the DUT to be enclosed in a safety-test enclosure with automatic isolation of the test points on the enclosure opening. This enclosure protects the test technician from electrical sources as well as from airborne particles caused by an unforeseen failure of the DUT that terminates in an explosion.

Class II Equipment

In Class II equipment, the absence of an earth requires protection via primary and secondary insulation. Hipot testing of Class II equipment involves much higher voltage levels, typically between 2500 and 4200 V. A common problem, particularly on new equipment, is that failure can be detected on the primary insulation that is undetectable by a hipot test on the outer surface, which tests the secondary insulation only. Testing programs must include both tests.

To test the primary protection, the selected method must access the primary insulation. This is essentially a contradiction in terms, because this connection needs to be inaccessible metal. However, experience shows the following options are feasible:

• Test the primary insulation prior to final assembly. Be sure to check that on assembly no degrading of this protection takes place (e.g., screws penetrating the insulation).

• Design the product with an access that can be permanently sealed after testing. This is often an element that product designers fail to anticipate.

• Design test jigs and probes that allow access through the enclosure, ensuring that the integrity of the product (in terms of the relevant standard finger tests) is maintained.

Testing also needs to be carried out on the secondary protection. Standards generally require that the product be wrapped in aluminum foil so that high voltages can be applied to all outer surfaces. This test may be practical for laboratory situations, but it is impractical for production testing, because of both the complexity in test setup and time required and because the outer surfaces of the product must be easily marked. The use of conductive foam in a special jig creates a nest or envelope around the outer surface of the product; test voltages can then be applied. Although this method is not quoted in standards, the standards authorities recommend this procedure.

Does Hipot Testing Degrade Insulation? The view that hipot testing is essentially a destructive test is often an area of discussion. This view originates from the use of flash in type testing where the long time period required provides potential for the degradation of insulation. However, in terms of production line testing, the reduced time period and the 5-mA trip setting significantly reduce this risk. The fact remains that many manufacturers successfully conduct the test without witnessing any degradation. Under certain circumstances, an ac flash test could corrupt sensitive electronic components.

Sensitive Equipment

In situations in which ac hipot testing could corrupt sensitive electronic components, the following solutions are possible:

• Use a dc hipot test. The voltage must match the specified peak ac voltage, which is achieved by multiplying the specified ac voltage by 1.414. A discharged facility following application ensures that no residual voltage remains.

• Use a soft dc hipot test. This test requires ramping up to the required voltage. In some instances, this test can benefit from ramping down as well. This process involves a slow ramp up from zero to the required value, and then holds for a timed period before ramping back down to zero and discharging the unit under test.

Suppression Devices

The advent of measures to control EMC has increased the use of suppression devices, but these can cause problems for hipot testing. It should be noted that most designers of such components have upgraded their products to meet the specified tests. However, in some cases the following solutions may be necessary:

• Disconnect such components. Some standards allow disconnection for safety testing. However, it is important to note that disconnection is often impractical for production line testing.

• Set higher trip levels (e.g., 10 or 15 mA). The use of this option should always be accompanied by the use of safety precautions such as key-locked switches, thereby ensuring proper authorization to conduct the test. The safest solution in such circumstances is to conduct the test with the test item housed in an enclosure and with appropriate interlocks. Such precautions do not need to be complicated or expensive to provide maximum operator safety.

• Apply the high-voltage test from a dc voltage source. Almost all standards now provide for this option. The test voltage is the ac level times 1.414 to provide the suitable dc test voltage. A dc voltage will ignore the capacitive leakage levels.

Conclusion

The hipot test is designed to indicate whether a product remains safe when subjected to high voltage and whether the user is protected from danger. Being able to prove that electrical or electronic products comply with the various standards is particularly important if a subsequent failure or fault is identified.

To demonstrate that a product has been tested properly, manufacturers must provide sufficient documentation. Many testers now automate the testing process on the production line and retain the results. Documentation through automated hipot testing maximizes protection from liability and provides effective proof at the end of the manufacturing process that a product is safe.

Reference: CE Compliance Engineering

Most people know what a continuity test is. A continuity test checks for good connections. Continuity tests are done by seeing if currents flow from point to point. If the currents flows easily the points are connected. “Hipot” is short for high potential => high voltage. Hipot testing checks that isolation is good. A hipot test is done to ensure that no current will flow from point to point.

Contnuity test = ensure current does flow from point to point.

Hipot test = turn up the voltage to ensure current does not flow from point to point.

Why test using high voltage?

A  hipot test is done to ensure that isolation is secure ie that no current is leaking out of the circuit. Good isolation guarentees safety to the user of electrical products.

Obviously this safety is a requirement in photovoltaic technology as well.

Common high voltage tests

1. Dieelectric Breakdown Test
2. Dieelectric Withstanding Test
3. Insulation Resistance Test

10.3.1 Purpose
To determine whether or not the module is sufficiently well insulated between current carrying parts and the frame or the outside world.
10.3.2 Apparatus

• a) A d.c. voltage source, with current limitation, capable of applying 500 V or 1 000 V plus twice the maximum system voltage of the module (as marked on the module – see Clause4) according to item c) of 10.3.4.

• b) An instrument to measure the insulation resistance.

10.3.3 Test conditions
The test shall be made on modules at ambient temperature of the surrounding atmosphere (see IEC 60068-1) and in a relative humidity not exceeding 75 %.

10.3.4 Procedure

• a) Connect the shorted output terminals of the module to the positive terminal of a d.c. insulation tester with a current limitation.

• b) Connect the exposed metal parts of the module to the negative terminal of the tester. If the module has no frame or if the frame is a poor electrical conductor, wrap a conductive foil around the edges and over the back of the module. If the module does not have a glass superstrate, also wrap the foil around the front of the module. Connect the foil to thenegative terminal of the tester.

• c) Increase the voltage applied by the tester at a rate not exceeding 500 V⋅s–1 to amaximum equal to 1 000 V plus twice the maximum system voltage (i.e. the maximumsystem voltage marked on the module by the manufacturer, see Clause 4). If the maximum system voltage does not exceed 50 V, the applied voltage shall be 500 V.Maintain the voltage at this level for 1 min.

• d) Reduce the applied voltage to zero and short-circuit the terminals of the test equipment to discharge the voltage build-up in the module.

• e) Remove the short circuit.

• f) Increase the voltage applied by the test equipment at a rate not to exceed 500 V⋅s–1 to 500 V or the maximum system voltage for the module, whichever is greater. Maintain the voltage at this level for 2 min. Then determine the insulation resistance.

• g) Reduce the applied voltage to zero and short-circuit the terminals of the test equipment to discharge the voltage build-up in the module.

• h) Remove the short circuit and disconnect the test equipment from the module.

10.3.5 Test requirements

• no dielectric breakdown or surface tracking during step c);

• for modules with total area less than 0,1 m2, the insulation resistance shall not be less than 400 MΩ;

• for modules with total area larger than 0,1 m2 the measured insulation resistance times the area of the module shall not be less than 40 MΩ⋅m2.