What is "Production Testing" for Product Safety?

Let's say you have a product that requires a product safety evaluation & approval, and you have gotten the product certified - congrats! Are you done? Not exactly...

If your product has a safety approval for North America (often called an "NRTL approval" - i.e. cULus, cETLus, etc) then there are requirements for ongoing safety testing on the production line. In this article, we'll review what those tests are, and what will be checked during factory inspections. If you want to learn more about factory inspections, check out our free article about this topic here: https://www.linkedin.com/pulse/product-compliance-factory-inspections-kevin-eldridge/?trackingId=Rp2trDFMQ5Kw705WSM%2BbJQ%3D%3D

The two main tests that are required during production are the "Hipot" test (aka "Di-electric withstand") and the "Ground Continuity" test.

Hipot test (aka "Di-electric withstand"):

This test is used to test the isolation of circuits.  The test is run by setting a “high potential” between the two circuits, and measuring any current between the two voltages.

WARNING - HIPOT TESTS (“DIELECTRIC WITHSTAND”) USE DANGEROUS VOLTAGES AND CAN CAUSE HARM OR DEATH.  NEVER TOUCH ACROSS THE TEST LEADS (I.E. ONE LEAD IN YOUR LEFT HAND, THE OTHER LEAD IN YOUR RIGHT HAND). 

The safety standard applicable to your product will spell out the exact requirements for isolation between circuits, and the corresponding required test voltages.  A common example of a hipot test:

• Class I product, metal chassis

• Hipot test run betweenLine & Neutral (tied together) of the AC input to the productThe grounded metal chassis

Any safety standard will likely require there to be “basic insulation” between the primary circuits and the grounded metal chassis.  A common voltage used to test basic insulation between primary and ground is 1500V AC.  A corresponding DC value can used by multiplying the AC value 1.414 (rms to peak).

Most standards state that “no breakdown shall occur” to determine whether or not the test passed.  This means no arcing, or measurable current (above a specified value) between the two probes of the tester. 

During the production line test, the test is typically only required to be run between 1 and 10 sections - again, be sure to double check the applicable requirements for production line testing from the applicable product standard. This will typically be listed in the NRTL report for the product. Here's an example:

Ground Continuity Test:

If your product is a “Class I” product (plugs into the wall and uses 3 prongs), the grounding methods within the product will be tested.  During the product approval, this is performed by running a high current through the longest ground path of the product (i.e. from where ground enters the product, to the furthest point of a metal enclosure) and measuring the resistance - this value cannot exceed a value specified by the standard (i.e. 100mΩ ). 

In the production line, this test is typically performed by a simple check of the continuity of the ground path (i.e. use of a simple digital multimeter). However, be sure to check the requirements for production line testing set by the relevant product standard - some may require using a higher test current for a short period of time.

Here's an example of the test verbiage from an NRTL report:

"Each product listed below shall be subjected to a test to determine that there is continuity between accessible dead-metal parts of the product and the grounding pin or blade of the attachment plug."

"If all accessible dead metal is connected, only a single test need be performed. A visual or audible device (ohmmeter, buzzer, etc.) may be used to indicate grounding continuity."

Summary:

By understanding the tests that are typically required during production, you can plan for them and avoid any mistakes / delays during your factory inspections.

That's it! By following the suggestions above, you can avoid problems during factory inspections that can be costly and cause delays. Please let us know if you have any comments or questions!