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Application of mains voltage on SIP/SOP connectors of medical device

#1
Hello,
I have a question regarding the application of mains voltage on SIP/SOP connectors of medical device => measurement of touch current on the metal enclosure according to figure 14 from IEC 60601-1 standard. When this requirement is applicable since all SIP/SOP connectors of medical equipment can be connected to secondary side of some other equipment. Can we simulate fault of those other equipment connected to medical equipment via different low voltage cables? Touch leakage current in this case will be FAIL since there is no separation between those SIP/SOP connectors to metal enclosure.
Thank you.
 

Benjamin Weber

Involved In Discussions
#2
I don't really understand your question.

Are you asking, if touch current measurement acc. fig. 14 has to be done with external voltage at the SIP/SOP?
- This depends on cl. 8.1 a), see this discussion: Isolation requirements for USB/Ethernet

Or are you asking, how the test is actually performed?
- If an external voltage has to be applied to the SIP/SOP (see above), it is usually applied to all pins incl. the shield connected together. This may also be mains voltage (see referenced discussion above)! If for example the shield is connected to a metal enclosuse that is protectively earthed (e.g. for EMC compliance), this will lead to excessive touch currents. In this case an SIP/SOP isolator should be used (to separate from secondary circuits, patient connections...) in combination with Y capacitors between SIP/SOP shield and enclosure and PE. Properly chosen Y capacitors will lead to EMC compliance (usually relevant for frequencies much higher than mains 50/60 Hz) and will efficiently isolate the shield from enclosure/PE during touch current measurement. Important note: In this case you have to be aware of the relevant requirements regarding the use of Y capacitors in 60601-1!
 
#3
But what in case that the following note provided within the user manual:
Equipment is intended to be connected to devices and connectors that comply with relevant IEC standards (e.g. IEC 60950-1 for Information Technology equipment, and IEC 60601 series for Medical Electrical equipment). Additionally, all such device combinations forming a system must comply with IEC 60601-1 (3. ed), Chapter 16 Medical Electrical systems. Any person or organization who has formed such a system is responsible for that the system complies with the requirements according to IEC 60601-1 in Chapter 16. If you are not sure, please contact a qualified technician or a local representative.
Is this warning sufficient for restriction as specified under clause 8.1.a???
 

Benjamin Weber

Involved In Discussions
#4
In my opinion this statement is equivalent to "connect only safe equipment - you are responsible" ;)

ISO 14971 has a clear hierarchy regarding the choice of risk control/mitigation measures in cl. 6.2:
  1. Inherent safety by design
  2. Protective measures in the actual medical device and/or manufacturing process
  3. Information for safety, such as labeling and instructions for use

As you can see, you are trying to go with the least favorable option. There are at two other options you should consider first. And eventually you have to convice the notified body, why did not choose those other options (e.g. an isolator as described above)! You will have a problem saying that implementation of such an isolator would be to expensive or complicated. This will most likely be not enough. And probably most test houses will discuss this with you.
 
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