Strategy for determining which components from a system should be "ME EQUIPMENT" -- home healthcare environment

#1
Hello everyone,

First post here, so I just want to say thanks for the wealth of information which is available on this forum. Greatly appreciated!

Onto the question -- I'm looking for some insight / feedback to a strategy I'm formulating for carrying out the EMC / safety testing for a medical device my company is developing. Specifically which items which are included in the purchase of our kit would be best to consider "medical equipment," and therefore be subjected to full 60601 testing.

The device itself is a small wireless gadget which is powered internally at 3.7V, and physically attaches to a patient using an adhesive. No electrical contact is made from the device to either the patient, or any sort of base station (data transfer is handled via bluetooth). This part obviously must be considered ME EQUIPMENT.

However, when the device is purchased it will also include a wireless charging pad and a 5V USB adapter w/ USB-C cable. Basically the mat is powered from a normal phone charger and there are no data ports etc. The only electrical connection on the entire pad is the female USB-C port which leads to mains.

From what I gather about accessories / ME SYSTEMS / external power supplies from reading 60601 and browsing this forum, it doesn't seem like it will be necessary to test the charging mat to 60601 fully. Reasons for this are:
  1. There are no "applied parts" on the charger (although it is going to be aimed at home healthcare clearance so the operator could also be the patient)
  2. The device cannot be used while being charged (it physically needs to be removed from the charger to expose the adhesive surface and stick to the patient)
  3. Maybe something else I'm missing?
My questions, then, are these:
  1. Am I correct in assuming that the charger will not need to be 60601 certified? (I realize it will require some consumer certification, like 62368-1)
  2. Is there any benefit which a full 60601 certification on the charger might buy me which a normal consumer certification will not?
  3. If I DO have to do full 60601 certification on the charger, how do I involve the USB adapter / cable in the testing? I.e. since the charger will be plugged into mains, will there be significant impacts to the structure of the charger safety tests, when compared to an internally powered device. Or, since the USB adapter and cable will meet relevant consumer standards (62368-1 for the adapter), can we consider it not to be a mains-connected part?
Thanks everyone for the help!
 
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Peter Selvey

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#4
For simplicity, it makes sense then to apply IEC 60601-1 to "set" of the charging pad and the patient device. It's easier for the paperwork and also having only one standard to apply.

It might seem that there is nothing critical in the charging pad but there are still relevant items such as correct design of parameters associated with a charging a Li-ion cell, testing of cell overvoltage/overcurrent protection (which may need to be done with the transmission side), temperatures during charging, impact of faults and abnormal conditions on either side (tx/rx) and so on, as well as basic labelling (identification of the manufacturer, model, other legal requirements).

When it comes to the "separate power supply" care is needed in interpretation in IEC 60601-1. There is nothing special required as there is no contact with the patient, so a generic approved USB supply (e.g. to 62368) can be assumed for the purpose of testing. The power supply should not be in the "scope of test" however obviously a power supply will be needed to perform the tests (e.g. testing what temperature the charging circuits get to). A good test report will identify which power supply is used in the tests. However, that should not be mistaken as meaning the power supply is the scope of tests, as long as it can be shown that the test results are not impacted by the power supply.

The operation manual should include the specifications (e.g. USB minimum current), a reference to being approved, and also it be limited to 3A to avoid flammability requirements. It makes sense to have a warning to the effect that any USB supply used should be purchased from a reputable manufacturer/store, noting that "fake" USB supplies bought from e.g. flea markets have been reported as starting fires/shock etc. That's nothing special for medical though.

If you plan to take the set to a test lab, you should discuss in advance and make sure they don't want to include the USB supply in the scope of test (even though it may be needed for testing).
 
#5
Thanks for the quick responses Peter, very helpful so far. I've been continuing to map out the standards which will apply to our system as a combined "set" as you recommend -- charger and device as separate pieces of ME equipment in an ME system.

I think I'm getting close to determining our exact test plan, but one thing I'm still getting hung up on is where the scope of testing ends exactly with ME EQUIPMENT; there are two angles on this I'm curious about specifically, both of which relate to one particular aspect of the charger piece. I have created and attached a diagram to represent my current thinking about the classification of different parts in the ME SYSTEM and aid with visualization.

The characteristic of the charger which is tripping me up is the fact that it does connect to a supply mains, but only by virtue of an accessory. Specifically an accessory which qualifies as 1 MOP between the charger and earth by virtue of it being a 62368 certified part. So, I'm curious if the charger pad itself qualifies as a MAINS PART or not? I am thinking that it does not, since it really only requires a plain 5V input at its appliance input, but am unsure.

In general, am I right in thinking there will be a large difference in testing the charger pad based on the answer to this question? As I interpret section 8 of 60601, this distinction would:
  1. Make a difference in determining which components MOOPS must be placed between (between enclosure & wall plugin VS. between enclosure & appliance inlet)
  2. Affect the working voltages of the system from which dielectric strength / creepage clearance requirements are derived.
  3. Probably a few others I could dig up by re-reading section 8
To focus down a bit more, I'm also curious specifically about its application to interpreting the following a specific section of 60601-1-2:
  • 60601-1-2 -- section 8.1, figure 2 (see attached pic)
    • This figure shows which type of ports present on the ME Equipment must be subjected to specific EMC tests
    • There are both A.C. input ports, and D.C. input ports labelled in this figure
    • My question is whether or not testing would be required at the A.C. port of the USB wall plugin, or just at the DC port where the USB cable attaches to the charger pad
Please let me know what you think, and thanks again for your time!
 

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Peter Selvey

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#6
Hmm ME systems ... don't get me started. Oh well. Coffee is in hand.

The original idea of a ME system as covered by Clause 16 was to address the possibility of cumulative leakage currents when there is more than one mains powered device in a system. For example, a dialysis machine that connects to a PC via a LAN connection and picks up the leakage from workstation PC, or a power board with 6 items plugged resulting in 2mA of earth leakage going down a single earth wire. It's the same problem that hotels need to deal with when you have 150 TVs all plugged into a single arial, the combined leakage can be huge.

In other words, not for the simple case of a 5V device powered by a single external power supply with just one connection to the wall supply.

However, the standard has evolved to so that the term "ME system" now appears throughout the standard and covers wider issues such as EMC.

This is legally dubious (or just outright wrong) and not feasible in practice.

Legally, a manufacturer is responsible for individual devices, as determined by the name that appears on the label. Separately, there is some responsibility for systems, but it is very limited in scope and does not rely on "type testing" the system (such as safety or EMC tests).

Consider that there are two devices X and Y by different manufacturers, Xm and Ym. Then, Xm instructs the user to connect X and Y to make a system. Legally, Xm should worry about compatibility and risks associated with interconnection, and take action to mitigate those risks. However, any action shall only apply to X. Xm does not and cannot take any responsibility for Y, such as electrical safety, EMC and other regulatory requirements.

Moreover, Xm cannot consider any tests (e.g. EMC test) of the combination of X+Y as a "type test" of the system. The reason is that a "type test", by definition, is intended to be representative of regular production. Unless Xm and Ym have a close contractual relationship where Ym agrees to provide all design and production data, risk analysis, design changes, factory locations, quality system controls etc etc etc, then there is no way that Xm can know if a test on a particular combination of X+Y is representative of all combinations of X+Y that are placed on the market.

But ... the IEC authors and the FDA scream ... how can you know if the system is safe if you don't test the system?

That's just life. For society the flexibility afforded by allowing X+Y without making Xm responsible for X+Y is preferable than the alternative. For example, Xm may specialise in ECG diagnostics while Ym in power supplies. Allowing them to work independently generally produces lower cost, greater options, higher quality systems than making Xm responsible for X+Y. Plus there is the huge overhead if Xm is responsible for X+Y, and society ends up paying for that.

So IEC & FDA need to suck it up. Xm still needs to consider compatibility/combination issues, but only actions that are practical for Xm to take are needed as risk controls. Making Xm responsible, for example, for EMC emissions of Y is not practical.

Now ... in actual tests on item X, it may be necessary to use X+Y to establish normal condition. This is different. The type test is still for X, and Y is just an ancillary item to get things up and running. The presumption here is that Y does not affect the tests. If Y does affect the results, it may be necessary to replace Y with a dummy device that representative of the worst case or modify Y so that it does not influence the result.

Example #1: Y is a USB power supply with a nominal output of 5V, and tolerance of ±0.2V. When testing X, this tolerance should be considered for each test. For example, in a temperature rise test, the temperature in X could be different at 4.8V vs 5.0V or 5.2V. If so, Y should be replaced by a variable power supply and adjusted to 4.8V, 5.0 and 5.2V to see the effect.

Example #2: It is planned to test EMC emissions of X. If X+Y is tested together and the emissions are below limits, obviously X alone is OK. Or, Y can be placed outside the test chamber or shielded, ferrites used to reduce noise from Y. Or Y can be replaced with a special low noise power supply.

Finally, it's important for Xm to have a good play with X+Y, so as to know if there are any potential issues arising from the combination. The key point is that any actions arising from this "play" should then appear as design solutions for X (for example, instructions on setting up a system, specifications for Y, design features in X to detect or minimise possible problems from Y). These can then be verified for implementation by Xm.

And the coffee is all gone!
 
Last edited:
#7
Alright, Peter, I think I definitely owe you a coffee now hah! Thanks for the lengthy and informative answer to my question.

Its good to know that there is a bit of stakeholder tension in the 60601 standards world regarding this type of use use of accessories, and also good to know what the best practices are from the manufacturer perspective.

This reasoning/testing strategy was something that myself and others in my company were converging towards, but struggling to find some concrete evidence for. You've provided some nice confidence that we shouldn't be expanding the scope of our testing responsibilities beyond the charger pad itself. I also feel like I have a much better level of knowledge that I can take into discussions with test labs etc..

Thanks for your time and effort!
~Walker
 
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