Medical device powered by IEC 60950-1 and IEC 62368-1 and IEC 60601-1-2 applicability

[FelipeSchneider]

Hello everyone,

I am making a test plan for a medical device that has the following characteristics:

• Battery-powered while performing the treatment.
• Charged in a receptacle, therefore, not able to perform the treatment.
• The charger is powered by an IEC 60950-1 and IEC 62368-1 compliant AC/DC wall power supply.

I am wondering if some IEC 60601-1-2 EMC tests still apply such as:

• Harmonic emissions (IEC 61000-3-2).
• Voltage fluctuations (IEC 61000-3-3).
• Electrical fast transients/Bursts (IEC 61000-4-5).
• Surge (IEC 61000-4-5).

For the emission tests (the first two of my list), I see no problem adding them to my test plan, but for the latter 2, I believe that they will damage the power supply since the limits required by IEC 60601-1-2 may be higher than those of IEC 62368-1.

Any thoughts?

 

[FelipeSchneider]

Additional info: checking similar devices IFUs, they state that as Not Applicable all EMC tests that are directly related to their power supply (which I believe is an IEC 62368-1 power supply).

So basically the 4 there I mentioned earlier + Voltage dips (IEC 61000-4-11) and Conducted RF (IEC 61000-4-6). This does not make any sense to me because the results of these last 2 tests are highly dependent on the device itself.

 

[Peter Selvey]

There's more at play here than you might think. It's not a matter of what the medical device manufacturer thinks is applicable because the medical device manufacturer is not the manufacturer of the power supply. Only the manufacturer of the power supply is responsible to decide what safety, EMC and other standards are applicable to their device, they are solely responsible for applying controls in both design and production to ensure continued compliance in regular production, not just the sample that was sent to a test lab.

Of course, anybody can send a sample to a test house for EMC testing for whatever criteria somebody dreams up. But without the responsibility for design and production control, which is legally tied to the entity that puts their name on the label of the object, it's just a floating test result with no practical meaning. It's not possible to refer to this as a "TYPE TEST" (which incorporates the manufacturer, responsibility, design and production controls in the definition) nor is it something that can be any part of a "declaration of conformity" which again is based on a sole entity that is responsible for controls to ensure continued compliance, not just the one off test report.

OK rant over

What does this mean for the medical device manufacturer? If the power supply is placed on the market together with the medical device, there is a responsibility to check the credentials of the power supply manufacturer and vet them to make sure they are legit and reliable, and to consider the risks that could arise from using an off the shelf IEC 62368-1 power supply. None of that means that the medical device manufacturer takes over as the manufacturer of the power supply, unless they go to the extent of relabelling the power supply under their name, which happens sometimes, but is a huge logistical exercise, not to be taken lightly. Assuming the normal light route is taken, the medical device manufacturer should just be spit balling possible issues and if appropriate, putting risk control measures IN THE MEDICAL DEVICE, where design and production controls with responsibility are possible. For example, if there's concern about voltage dips, add a bunch of 470µF capacitors or a battery or store vital info in non-volatile memory, all of which can be designed, tested and production controlled by the medical device manufacturer independent of the power supply manufacturer.

Sorry, I'm ranting again.

If you are looking at the standards and FDA guidance, they can suggest that the medical device manufacturer is somehow responsible for the power supply. Ignore the suggestions. Check the detail. It's not possible for one manufacturer to be responsible for another manufacturer's product.

 

[FelipeSchneider]

I understand your point, Peter.

I believe that the medical device in question is safe and that the team is doing a good job on the documentation and specification side. However, at the end of the day, I also have to consider what the FDA will think about the tests I have performed and what the Lab Engineer will think about the requirements that I have set.

The crux of my question is that it is clear to me that I can use a non-medical device power supply to power the charger since the medical device will not be in contact with the patient and only the operator will have access to it during that usage phase. BUT, this same power supply may not withstand some of the IEC 60601-1-2 immunity tests, which is somewhat problematic in my mind. Maybe I am mistaken about the applicability of these tests.

 

[Peter Selvey]

The original issue is a worry that if you test IEC 60601-1-2 on the system of PSU + MD, some items could fail, and anyhow the results seem to be highly dependent on the power supply, which is not made by your company. What I'm saying is when faced with issues like this, it should be a flag that something fundamentally is wrong in the way of thinking. EMC won't be the only case like this. While it's important to consider the system when analysing compliance (standards, regulations, risk management), in the end, the output of the analysis should be specifications and criteria for the individual device, not the system. If you end up with a criteria that applies to devices outside of your responsibility, then something has gone wrong with the analysis.

Unfortunately, at this time the standards and FDA guides don't really understand this, and we have things like ME SYSTEMs being tested for safety EMC, but I expect this will get fixed in the future. There are internal conflicts within the standard (definition of manufacturer, type test, selection of samples) which can't be met for systems that contain items from other manufacturers, and legally and logically it doesn't make sense. The concerns you have raised are just one of many logistical and legal issues that arise when testing a system that contains items that are placed on the market by different manufacturers. It's all a massive fudge.

For now: I don't keep the latest versions of EMC standards, but there is a clause 4.2 in the 2014 edition. This states that non-ME equipment used in an ME system should comply with the EMC standards for the non-ME equipment (makes sense), and if EM ENVIRONMENT of use could result in a loss of basic safety or essential performance, then the system should be tested for IEC 60601-1-2. In your case, you could reasonably argue that it's not possible to affect basic safety or performance since it's only used for charging only.

There is an argument that since the charger is for (presumedly) Li-ion batteries that basic safety is still applicable and hence the test is required. But here again there is a logic error: if the exploding batteries is really a concern, would you just rely on an EMC test on one sample? No reasonable person would do this. In reality there are multiple levels of protection in a battery charging system (cell protection, PCMs, charging circuit design, thermistors etc.) that are independent of and don't rely on the power supply to function. That's the way it should work, in a system of PSU + MD, there is a risk of exploding batteries but the analysis shows the risk control measures are reasonably be implemented in the MD, and can be specified and verified totally independent of the PSU.