Charging Port as an Accessible Part and Required MOP

[ktsourapas]

Hi all,
We have designed a medical-grade wristband that needs to comply with the IEC60601-1 standard.
The device operates with a rechargeable battery and cannot be used while charging.
As a result, I have already implemented 2-MOOP in the charging cable that was adequate till now. The patient is not able to touch the charging port during use.

The problem is that the manufacturer has increased the charging port's dimensions due to manufacturing limitations (the port was not big enough to hold the cable in position). As a result, the patient is now able to touch the metal pins of the charging port. From my perspective, the port is now considered an accessible part and requires 2 MOPP according to the finger test. This results in a huge redesign that I would like to avoid. So, I have asked the manufacturer to make the pins not accessible somehow e.g. making the pins shorter than the surface.
However, the manufacturer insists that additional protection is not required and that we just need to limit the voltage and the current of the charging IC.
Am I missing something?

 

[Peter Selvey]

The port is always an accessible part regardless of whether the pins are accessible or not, and the accessibility of the pins does not change MOOP into MOPP. That decision is based on the intended purpose and normal use. If during charging, the "medical device" is not in use on the patient, then charging mode can be considered to be operator only (the patient becomes an operator for that phase of use).

There are various options to handle the accessible pins. One option is to treat the charger as a non-medical device, and only needs to comply with IEC 62368-1 (or IEC 60950), which allows the contact with the pins. Or if it's preferred (e.g. for simplicity, marketing) to have the charger tested to IEC 60601-1, you can make use of 8.4.2c which allows contact with low voltage pins (e.g. 5Vdc) that are 2MOOP from mains. It's a bit messy but the pins are totally safe to touch.

 

[ktsourapas]

Hi Peter,

Thank you for your quick reply. Your comment regarding charging by the operator is clear.
Based on the lack of use while charging, we have implemented a 2 MOOP in the charging cable to isolate the pins of the charger from mains and protect the operator/patient.
However, this has to do with the charger and the cable while charging.

My concern has to do with the device and the exposed pins of the charging port while the device is worn.
As you mentioned, the complete housing, including the charging port, is considered an accessible part.
Before the update, the pins were not accessible and the 2MOPP requirement was fulfilled by the air clearance value.
Now, the patient can directly touch the exposed pins, and there is not enough clearance. How can I justify that this is not an issue for the patient's safety?

 

[Peter Selvey]

Ahh OK, I was thinking it was the charger side pins. Often charging devices have the male pins on the charger side, which then connect to the actual device by spring loading or clips. Also these days many designs just use USB connectors, like Type C or B. Anyway, I get it, the device itself has accessible contacts.

This is still not a safety issue as the voltages are safe in the real world. However, it can be a compliance issue, and it will depend a lot on the device itself, e.g. does it have an electrode, what's the internal circuit from the pins e.g. does it have a blocking diode or does the electrode(s) have series resistance, and whether this will be an in-house assessment vs a third party lab that might want to come in hard with 1kV tests and blow up the device, or expect 3.4mm clearance. Assuming the device is totally worn on the patient, this only affects patient auxiliary currents, and normal electrical components can be used to limit currents, not larger MOPP. But that's based on a nuanced argument and not a widely accepted view.

 

[ktsourapas]

Thanks again Peter.
Unfortunately, the case is that we use a third-party lab that will ask for the 2 MOPP...
It is awful to have to perform design changes at this point in production with an already finalized stack-up.
Do you have a suggestion for a component that could minimize the impact in terms of space?

 

[Peter Selvey]

Does the device have electrodes, or is it just a plastic applied part with no electrical contact to the patient?

 

[ktsourapas]

There is one patient connection (1 pair of electrodes) which are implemented in the strap of the wearable (wristband) and are in contact with the patient's skin. The electrodes fulfill the requirements for the auxiliary current in both normal condition and SFC.