After completing your electrical safety testing (EST) and the test laboratory has imposed routine production line testing on your device, did you ask yourself these questions?
As a Regulatory Specialist with more than ten years of experience in conducting safety testing, let me shed light on medical production line testing to help you understand the process and why it’s essential in the successful development of medical devices.
Standards such as 60601-1, Medical Electrical Equipment: General Requirements for Basic Safety and Essential Performance, utilize what is referred to as “type tests.”
Type tests are tests on a representative sample of the equipment to determine if the equipment, as designed and manufactured, can meet the requirements of the standard1. It’s important to note the definition of type tests indicates testing is to be performed on a (single) representative sample.
Although more than one sample can be provided and used for electrical safety testing, more often than not, a single sample is provided for evaluation and is either modified or repaired as necessary to meet the requirement of the standard.
But there’s a problem.
If you’re only testing one sample, what assurance do you have that all devices coming off the production line and entering the market are compliant?
Standards often recommend manufacturers carry out measures during the manufacture of a device to ensure each item coming off the production line satisfies all standard requirements, even if it's only partially tested individually during the manufacture.
My recommendation is to consider employing one or more of the following:
Of the options above, most manufacturers employ the first option, good manufacturing practices via an accredited quality management system such as ISO 13485 Medical Devices – Quality Management Systems – Requirements for Regulatory Purposes, and option 2, routine production line testing.
Director of Regulatory Affairs for Biotex and Laboratory Manager for Criterion
Routine production line testing is conducted on every device that comes off the production line. These tests typically vary from type tests in that they are modified to suit manufacturing conditions and reduce the risk of compromising the integrity (safety) of a commercial device while still provoking the worst-case situation.
For a medical device, routine production line testing should cover critical insulation of the mains part, patient connections, and the insulation or separation between such parts. Often dielectric strength, ground continuity, and leakage current tests are selected because they are good indicators of safety-critical manufacturing errors.
Dielectric strength tests the ability of an insulating material or system to resist breakdown. During this test, a high voltage, typically in the kV range, is applied across the insulation barrier for a period of time. If the insulation breaks down, the test is considered a failure. Insulation breakdown is deemed to have occurred when the current rapidly increases in an uncontrolled manner.
Ground continuity tests ensure grounding is continuous (unbroken) from the fixed wiring, power cord, or appliance inlet to various points of the equipment, typically the chassis, which are required to be grounded. Unlike the ground bond type test, where the grounding scheme is stressed using 25 A, or more, the ground continuity test may be conducted using an indicator light, ohmmeter, or other simple means to show ground is present.
Leakage current is a measurement of the non-functional current which can flow from various parts of a piece of equipment to the ground or from one part of the equipment to another. Under normal conditions, leakage current should flow safely through the ground conductor and away from accessible parts or applied parts; however, when there is a manufacturing issue in the device, leakage current can become accessible and cause an electric shock.
Each device is tested for resistance to breakdown using an ac or dc voltage. If dc voltage is used, the stated ac values suggested below must be multiplied by 1.414.
Tests are conducted between primary circuits (line/neutral) and:
It’s crucial for on/off switches to be in the “on” position during testing for the test to be considered valid.
The current edition of 60601-1 and relevant guidance documents do not provide specific values for production line dielectric strength tests. However, expect the manufacturer to determine appropriate values using their risk management process.
As previously discussed, the intent of production line testing is to detect gross manufacturing errors and not repeat type tests that could damage equipment. As such, and to provide a uniform approach across the industry, many organizations revert to the guidance provided in UL 60601-1:2003 (the US version of IEC 60601-1 second edition). Either test condition A or B of the following table may be used.
Breakdown constitutes a failure. Insulation breakdown is considered to have occurred when the current that flows as a result of the application of the test voltage rapidly increases in an uncontrolled manner. Corona discharge or a single momentary flashover is not regarded as insulation breakdown2.
Each device that has a provision for grounding is tested using an indicating device, as explained in the previous section. The indicating device is connected between the terminal used for connecting to the supply mains ground and any accessible dead metal parts of the device that are likely to become energized in the event of a fault. If all accessible dead metal parts are contiguous, only one test needs to be conducted; otherwise, multiple tests of each of the accessible dead metal parts will need to be conducted.
The ground wire should be flexed along its length during this test while observing the continuity indicator. If there is no continuity or a change in continuity, then the ground connection may be damaged. The test should be considered a failure, equipment quarantined, and additional investigation should be conducted to determine the root cause.
Note: Ground continuity is not required for devices that are permanently connected by fixed wiring since such a device would need to be installed by a qualified electrician, and ground would be verified during installation.
Leakage current is measured in series with the ground pin or terminal of Class I (grounded) equipment. If the device is Class II (ungrounded) but contains functional earth, it needs to be tested as if it were Class I equipment.
A suitable measuring device, such as the one illustrated in Figure 12 of IEC 60601-1, must be used to measure leakage current accurately.
Terminals “Z” are connected in series with the ground conductor for the equipment, as shown below:
The test setup illustrated above utilizes a custom switch box for more advanced testing. For production line testing, it is recommended the measuring device be constructed to incorporate an AC mains inlet and AC mains outlet, which will simplify the test setup and reduce setup errors.
Utilizing the device's highest-rated mains supply voltage, measure the voltage across capacitor C1 with a volt meter having a resistance greater than or equal to 1 MΩ and a capacitance greater than or equal to 150 pF. Using the value of R2 and Ohm's law, calculate the leakage current.
Leakage current over 5 mA constitutes a failure. Equipment should be quarantined, and additional investigation should be conducted to determine the root cause.
As a medical device manufacturer, you should have a quality management system. This system can be utilized to document the required testing, perhaps in an assembly procedure, and the test records can be saved in a traveler or quality form. If your device carries an NRTL Mark (UL, CSA, TUV, Nemko, etc.), these records will be of particular interest to them when they perform onsite audits of your facility two to four times per year.
There are a few reasons why production line testing may not have been required or may have changed for your previous device:
1. None of the tests were applicable. For example, if your device is internally powered, there is no ground, so ground continuity testing would not be appropriate. The test points previously indicated for dielectric strength and leakage current are also not present; therefore, no testing is required.
2. The level of certification you requested from your test laboratory did not require production line testing. You can get a few different levels or types of certifications for a product. To simplify, we will discuss the NRTL Mark and self-declaration style or CE-type reports. If you requested an NRTL Mark, the issuer of the mark takes some stake in assuring continued compliance of your device. As such, they are interested in ensuring every device coming off your production line is identical to the device they tested in their lab. One way to do this is to require, you guessed it, production line testing. You are solely responsible for continued compliance with a self-declaration style report, so the test lab most likely did not mention anything about production line testing.
3. The standard changed. Yeah, that happens! Take UL 60601-1:2003, for example. This standard contains Annex DVB, a US national difference covering the requirements for production line tests. This annex calls out three specific tests: dielectric voltage-withstand (dielectric strength), ground-continuity, and single suspension (only for suspension systems without a safety device). ANSI/AAMI ES60601-1:2005 & A1:2012 & A2:2021 is the US version of IEC 60601-1 third edition, which is the most current edition of the 60601-1 standard. In the US version, there are no national differences addressing production line tests; as such, the testing is imposed on a case-by-case basis, as indicated in the previous point, or the manufacturer follows the recommendations set forth at the beginning of this article.
At Criterion, we know production line testing requirements and their application can be confusing. We hope this article clarifies any questions you have, but if you still have questions or would like to request free datasheets for production line testing, please reach out to us at criterion@biotexmedical.com
Wade is the Director of Regulatory Affairs for Biotex, Inc. and the Laboratory Manager for Criterion, a Biotex, Inc. service. He has worked in compliance for over 14 years, including standards development and electrical safety evaluations with a specialty in medical devices. Throughout his career, Wade has worked for Certification Body (CB) and Nationally Recognized Testing Laboratory (NRTL) test laboratories and medical device manufacturers.
