Insulation class II device with metal enclosure

[EMengineer]

Hi everyone. We have device which is powered by external PSU. As most PSU's its output does not have protective earth connection. In our case we have metal enclosure with secondary circuit inside it (voltage up to 24VDC).
Shall the metal enclosure be separated from all circuits by 2 MOP (J.2 insulation example) - no gorunding with enclosure? SIP/SOP is double insulated (for mains voltage). Although SIP/SOP connector may touch the enclosure (in this case it should be plastic or separated by 2 MOP distance?).
Does the separation between secondary and enclosure also would ensure that there is no risk of operator touching the enclosure and the patient at the same time which would deliver too high leakage current?
In this case PSU would be insulation class I and device insulation class II?
Maybe there are points that I missed?

 

[Peter Selvey]

Insulation Class (i.e. Class I, Class II) is purely mains related and specifically the connection to the mains. It lets the user know if they need a two pin plug or three pinned plug. No matter what the insulation strategy is for various parts of the equipment, the equipment remains Class I or Class II (one or the other) in principle based on the mains connection (there are some weird exceptions for functional earths ... but that is another story).

After the mains connection, different strategies can be used as long as they are effective. For example you could bond (deliberately connect) all the metal parts of the enclosure together such that it is not possible for the 24V to get out like a faraday cage. Or at least, bond any metal parts that are near secondary circuits. This is kind of like earthing and probably the most common way. The bonding needs to be good enough that it can carry the maximum current from the 24V supply without breaking. For the sake of avoiding confusion, you could also connect the 0V line of the 24V circuit to the metal parts as well, that makes it clear especially if you are dealing with test labs.

If the metal enclosure can contact the patient, there could be a lot more to the story. It will depend on the classification (B, BF CF etc), parts of the equipment that contact and so on. It is not simple to explain.

The SIP/SOP can be excluded under 8.4.2c or can be designed in such a way that there is insulation around the part.

 

[EMengineer]

Thank you Peter for the response. So insulation class is a PSU matter. If device is separate from the PSU it does not have any insulation class.
To add to your answer I found other thread with your response about Annex J insulation examples:
Isolation of secondary grounded circuits
To sum up - no need to worry about low voltage secondary circuit within unearthed metal enclosure (if mains part is in external PSU). The most important thing is to pay attention to the correct separation of the applied part (2 MOPP for working voltage and 1 MOPP for mains voltage).
Although I have a little fear how testing house will evaluate this part (I saw in other threads that manufacturer had to put Y caps to comply with annex J example, even when it is only informative annex).

 

[EMengineer]

Insulation Class (i.e. Class I, Class II) is purely mains related and specifically the connection to the mains. It lets the user know if they need a two pin plug or three pinned plug. No matter what the insulation strategy is for various parts of the equipment, the equipment remains Class I or Class II (one or the other) in principle based on the mains connection (there are some weird exceptions for functional earths ... but that is another story).

After the mains connection, different strategies can be used as long as they are effective. For example you could bond (deliberately connect) all the metal parts of the enclosure together such that it is not possible for the 24V to get out like a faraday cage. Or at least, bond any metal parts that are near secondary circuits. This is kind of like earthing and probably the most common way. The bonding needs to be good enough that it can carry the maximum current from the 24V supply without breaking. For the sake of avoiding confusion, you could also connect the 0V line of the 24V circuit to the metal parts as well, that makes it clear especially if you are dealing with test labs.

If the metal enclosure can contact the patient, there could be a lot more to the story. It will depend on the classification (B, BF CF etc), parts of the equipment that contact and so on. It is not simple to explain.

The SIP/SOP can be excluded under 8.4.2c or can be designed in such a way that there is insulation around the part.

I couldn't find any specific information in the standard regarding the scenario where an unearthed metal enclosure becomes accidentally earthed through contact with other equipment, it's possible that I may have missed something. Could you please clarify if there are any specific considerations in the IEC 60601-1 standard for this situation? The earthing probability seems to be high, but the applied part remains unaffected due to proper separation. In this particular scenario where mains voltage is present on unearthed metal parts (Fig 18 of 601-1), even though unintentional earthing can occur at times, how should the evaluation of leakage current be conducted?
I have another question regarding leakage currents, specifically in a device with a CF applied part. If the operator can simultaneously touch both the metal controller and the patient, should the controller be considered as a part to which the requirements for the applied part (in this case, CF) are applicable (as per 601-1 cl. 4.6)? Then the controller shall be insulated from the other circuits by 2 MOPP, be of insulated material and pass 10 uA leakage current requirement?