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ELECTRICAL SAFETY COMPLIANCE TESTING
Instruments & Systems

Hipot Safety Testers



 

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Hipot / Electrical Safety Testing FAQ's

Design and production engineers trust CHROMA's hipot testers and safety analyzers for their applications. For years, CHROMA has been a go-to supplier of electronic safety test equipment to appliance, commercial, and medical industries and the applications keep growing.

General

The obvious answer is that products are regulated to protect consumers and operators from shock hazards. Shock hazards exist when a potential voltage and current are accessible to the operator with respect to earth ground. Electrical safety tests occupy very little time on the production line, but reduces the risks to operator and consumer considerably.

At the point of manufacture, before the product is available to the end user. Manufactures of electrical and electronic products need to insure that no hazardous voltages or currents are accessible to the user. They need to test their products to determine if they meet minimum safety levels. In order to do this, they need to test against a reference or standard.

Electrical shock is caused by current through the human body. Studies have concluded that the human body can feel the sensation of an electrical shock with as little as 1.0ma of current. Since the human body is not a fixed resistance, the voltage required to produce 1.0ma of current can vary greatly based on the minimum impedance of the human body under various conditions (some models use a human body resistance value of 1K ohms up to 100K ohms).

Primary testing includes four kinds of tests: Dielectric Withstand (Hipot Test), Isolation Resistance Test, Leakage Current Test, and Ground Continuity.

The first step in selecting safety test equipment is to understand your basic requirements. It may be the safety standard your product needs to comply to. The appropriate safety test equipment is not only selected in accordance with safety standards but considers functional product requirements, cost and efficiency. For example auxiliary accessories like HV Guns, fixtures, and software control can increase test efficiency. It is our recommendation to give us a call to help select your equipment.

Almost all DUTs are equipped with a charged capacitor when testing DC Voltage. To avoid electrical hazards it is necessary to discharge the capacitor to a regulated voltage value at the end of the test. However, the higher capacitance value, the longer it takes to discharge, directly impacting the efficiency of the process. Our safety test equipment includes a fast and reliable capacitor discharge circuit to ensure production efficiency and safety.

It may occur DUT no contact or bad contact condition during test procedure, especially in production line of emphasizing efficiency occurs more easily. The DUTs which are no contact, bad contact, test line damage or short circuit will judge no good product as good product or damage the equipment then cause the unnecessary risk cost. Thus, a lot of safety test equipment will judge if there is bad contact by low limit or high limit of current, this method interference factor too much so can’t judge effectively. The excellent safety test equipment filter short circuit DUT or judge circuit bad contact by more accurate judgment method (OSC) to save the production cost of manufacturers.

All personnel of operating test equipment need to accept basic electronic theory training to realize the effect of current on human body and how to avoid electrical shock, familiar with test environment and precaution for emergency condition occurred. Some test equipments are with interlock function to prevent improper operation. When the personnel realize the previous described items then to explain operation procedure and test purpose about the condition of no good product and test fail occurred. Since the safety tests mostly are high voltage or mass current test, the test personnel should be pay more attention while testing.

In Europe, the safety for manufacturers and test personnel of laboratory had performed for many years. The manufacturers and test personnel of electronic appliances, technology product, household appliances, mechanical tool or miscellaneous equipment, there is chapter to regulate in various safety regulations. The contents of UL, IEC and EN include grounding status of test area marking (personnel, instrument and DUT position), equipment marking (marked with "dangerous" specifically or the item in testing), equipment worktable and etc and electrical insulation capability of various test equipment (IEC 61010).

UL

www.ul.com

American Underwriters Laboratories Recognized Administration

ANSI

www.ansi.org

American National Standards Institute

BSI

www.bsi.org.uk

British Standards

CENELEC

www.cenelec.org

European Committee for Electrotechnical

CSA

www.csa.ca

Canadian Standards Association

VDE

www.vde.de

Germany Electronic Electrical Information Association

IEC

www.iec.ch

International Electrotechnical Commission

JSA

www.jsa.or.jp

Japanese Standards Association

IEEE

www.ieee.org

American Institute of Electrical and Electronics Engineers, Inc.

ISO

www.iso.ch

International Organization for Standardization

OSHA

www.osha.gov

American Occupational Safety & Health Administration

TUV

www.tuv.com

German TUV Recognized Administration

CCC

www.cccn.org.cn

People’s Republic of China Enforced Product Recognized Center

NSSN

www.nssn.org

National Resource for Global Standards

BSMI

www.bsmi.gov.tw

Bureau of Standards, Metrology & Inspection, MOEA, R.O.C

Chroma

www.chromaate.com

Chroma ATE INC.

AC/DC Dielectric Withstand Test (HIPOT)

Hipot test is one of safety test being often seen. Often seen dielectric withstand, high potential and hipot test all denote withstanding test. The mainly purpose of hipot test is for testing insulating capability of DUT(Device under Test). When the equipment is operating, apply a high voltage to test point for testing whether insulation breakdown or electrical flashover/ARC are occurred.

The insulation is divided into four types: Basic, Supplementary, Double and Reinforced. Because product inside may be over dirt, wet or other reason cause discharge along surface, thus judge if circuit design inside product has problems of distance along surface or insulation insufficiency by hipot test.

Please notice that may has difference between total current and real current cause by partly internal capacitive reactance. The curent is outputting, if capacitive reactance is higher and reactive is higher, this makes real current lower relatively. If the user can’t measure output current accurately, it will cause a blind spot in testing.

DC hipot test usually need to add ramp time and fall time, because mostly DUTs are with capacitance and causes charging current generated(figure 3). For charging current steady, ramp time is needed for buffering then leakage current won’t over high because of charge current and judge as FAIL.

Because hipot test will cause DUT discharge, thus need a period of time for discharging after hipot test is ended. A fine hipot test equipment will descrease fall time to the minimum and mark danger warning before reaching discharge standard for protecting the testers from electrical shock.

Flashover is an electrical breakdown of a gas that produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. Vasily V. Petrov, a Russian scientist who discovered it in 1802, first described the phenomenon.

The test voltage of standard is the mainly factor for judging good product in hipot test. A lot of hipot test equipment convert low voltage into high voltage by transformer then output it, but internal impedance of instrument will cause divider especially in some bad quality hipot test equipment, its actual output voltage can't reach safety standard. For avoiding error to judge as good product and cause unnecessary trouble, fine hipot test equipment will auto gain compensation to modify and compensate voltage to needed voltage value and design the voltmeter on the output terminal for measuring accurately whether output voltage is insufficient.

Ground Bond Testing

Ground protection testing consists of two methods: Ground Continuity test (GC) and Ground Bond test (GB). The purpose of ground protection testing is for protecting users from electrical hazards as touching equipment when unsuitable current is created and flows to the earth.

Insulation Resistance Testing (IR)

Insulation resistance test and DC withstand test are very similarity, apply DC voltage (50~1000V) to two points of connecting for judging good and no good product. Insulation resistance test is nondestructive test and can detect if insulation is good. Some regulations require insulation resistance testing first, then withstand testing. When an insulation resistance test doesn't pass usually withstand voltage test will also fail.

Leakage Current Testing (LC)

In low voltage and electronics Leakage Current is any current that flows when the ideal current is zero. In medium and high voltage applications it is the current that flows either through the body or over the surface of an insulator. The difference between leakage current test, withstanding voltage test and grounding protection test is equipment testing under running status. The leakage current adds a human body simulation impedance circuit in testing, it can simulate the quantity of leakage current through human body under real conditions.

Whatever national standard regulation or region standard regulation, the standard of leakage current is different by the insulation types of products. “CLASSI, II, III” are mainly in consideration of the insulation system of product which derived from IEC system, brief descriptions are as below:

  • CLASS I indicates anti-shock protection of product not only depends on basic insulation but also includes grounding method.

  • CLASS II indicates anti-shock protection of product not only depends on basic insulation but also includes additional precaution. For example double or reinforce insulation but without grounding or installation condition for relying precaution.

  • CLASS III indicates anti-shock protection of product depends on power voltage is safety extra-low voltage (SELV) and it don’t generate danger voltage.

The leakage current with different test mode by various safeties and different leakage current standard by various test point. The most often seen is that the current flows through DUT to E terminal of power, the human body touches E terminal of product will cause induction we called it earth leakage current. When earth leakage current is testing input 110% rated voltage to add human simulation circuit and judge if the current value of flowing through human simulation circuit is over the limit value of leakage current. In addition, there are Patient Leakage Current, Patient Auxiliary Leakage Current and etc leakage tests.

The definition of medical equipment is the physical or electrical contact with patients (mostly regulations denotes human being, Europe regulations denotes human being and animal), applies to the equipment of diagnosing, treating and monitoring. The leakage current testing of medical equipment emphasizes on Applied part under normal using status by physical method to contact patient or accessories and facilities the patients need to touch such as probe, electrocardiogram, blood pressure bar and operating table. All types of leakage current will cause electrical hazards to patients and operators.

The current flows from the power terminal through DUT to E terminal of power as product running.

The current flow from two kinds of power terminal through DUT to accessible part of chassis, touch point and screw products, created inductance as human body touch, we called it enclosure/touch/chassis leakage current.

Patient leakage current consists of three kinds of test. The first test is the current flow from power terminal through applied part to earth terminal as product operating;Another test of patient leakage current, power source applies to MD by 110% the highest operating voltage. Make the current flows through applied part, accessible part then to earth terminal;The third test of patient leakage current, power source applies to SOP/SIP by 110% the highest operating voltage. When the product is operating, the current flows from two kinds of power terminal through applied part, MD then to earth terminal.

When the product is operating, the current flows from test point of applied part through MD to another test point of applied part then to earth terminal.