General questions about Medical Device MOPs and MOPPs

M

maxruben

#11
Also note that accessible parts may need to be subject to the requirements for applied parts if they can come into contact with the patient. This should be assessed by the risk management process. See clause 4.6 in IEC 60601-1.

/Ruben
 
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DENich

Involved In Discussions
#13
Hello all.
I didn't know whether I should start a new thread or continue writing here to prevent clogging of the forum. It is still “general question” so I have decided to write here.

The standard 60601-1 rev.3.1 in Annex J ''Survey of insulation paths'' claims that we should have 1 MOP between a PROTECTIVELY EARTHED ENCLOSURE AND a SECONDARY CIRCUIT (please, see Figure J.1 – Insulation example 1).

I believe, that in case of using our capacitor charger and providing 2 MOPs between the MAINS PART and the SECONDARY CIRCUIT we don't need to provide any MOPs between the PROTECTIVELY EARTHED ENCLOSURE AND the SECONDARY CIRCUIT. Please, see my rationales in the attachment (Qstn_MOP_bwn_SP&enclosure.pdf). Do my rationales have any mistakes? What do you think?
.
 

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M

MedMartin

#14
Hi Denich,

I would say your argumentation is valid.

The reason for the 1 MOP in J.1 is that there has to be an isolation for the applied part to limit patient currents from secondary voltage. And in from figure J.7 there is also the requirement for 1 MOP for mains voltage (mains on applied part). But since your device has no applied part there is also no requirement.

The operator and patient may touch the enclosure connected to protective earth without risk and is even in case of an error protected by 2 MOPP.

Best regards,
Martin
 

VinceTech

Involved In Discussions
#15
Hi Denich,

I would say your argumentation is valid.

The reason for the 1 MOP in J.1 is that there has to be an isolation for the applied part to limit patient currents from secondary voltage. And in from figure J.7 there is also the requirement for 1 MOP for mains voltage (mains on applied part). But since your device has no applied part there is also no requirement.

The operator and patient may touch the enclosure connected to protective earth without risk and is even in case of an error protected by 2 MOPP.

Best regards,
Martin
Hi Martin

Just want to discuss more about this. I think even there is no applied parts. Any parts accessible by operator such as enclosure shall be 2MOP protected from secondary and mains voltage.
If enclosure is protective earthed. Then another layer insulation providing 2MOP secondary working voltage is still required.

Please comment, if this is right?
 

DENich

Involved In Discussions
#16
Thanks a lot for your reply, MedMartin.
In spite of spending a lot of hours on reading 60601-1 some general issues still have stayed unclear.
The reason for the 1 MOP in J.1 is that there has to be an isolation for the applied part to limit patient currents from secondary voltage. And in from figure J.7 there is also the requirement for 1 MOP for mains voltage (mains on applied part). But since your device has no applied part there is also no requirement
As I tried to show in Qstn_MOP_bwn_SP&enclosure.pdf the limitation of patient currents from secondary voltage depends on quality of the separation of the MAINS PART and the SECONDARY CIRCUIT (i.e from a transformer TR, clearances and creepages etc.). Therefore, I claim we there is no need to provide MOPs between the SECONDARY CIRCUIT and the PROTECTIVELY EARTHED ENCLOSURE.
As I've understood from the standard Figure J.7 concerns to F-TYPE APPLIED PARTS which is not my case.
Also, I want to add that despite the capacitor charger has no APPLIED PARTS it is a part of ME DEVICE and this ME DEVICE may has APPLIED PARTS and these APPLIED PARTS may have an electrical connection with the enclosure of our capacitor charger.
The operator and patient may touch the enclosure connected to protective earth without risk and is even in case of an error protected by 2 MOPP.
I'm sorry, but I'm not sure I've understood this sentence correctly. Could you explain what you wanted to say?

Den
 

VinceTech

Involved In Discussions
#17
Hi DENich

Just think the fault condition where patient is mains potential due to failure if the other equipment patient connected to. In this condition, the applied part shall provide sufficient MOP to limit the current flowing from the patent connections to your equipment.

Regards,
 

DENich

Involved In Discussions
#18
Just think the fault condition where patient is mains potential due to failure if the other equipment patient connected to. In this condition, the applied part shall provide sufficient MOP to limit the current flowing from the patent connections to your equipment.
Hi VinceTech,
Could you specify paragraph of 60601-1 where described that NORMAL CONDITION or SINGLE FAULT CONDITION include appearing a MAINS potential on a body of a PATIENT? As far as I'm concerned, appearing of a MAINS potential on a body of a PATIENT is considered only for F-TYPE APPLIED PARTS (8.5.2.1). We don't have F-TYPE APPLIED PARTS. Actually, our module has no APPLIED PARTS at all, but a ME DEVICE where our module can be installed can have B-TYPE APPLIED PARTS. For B-TYPE APPLIED PARTS only earthing of a PATIENT is considered as NORMAL CONDITION. I could be wrong. Please, let me know if it is so.

Best regards,
Den
 
M

MedMartin

#19
Hello VinceTech,

The protective earth counts as 1 means of protection.
Even applied parts of type B may be connected to protective earth.

Best regards,
Martin
 
M

MedMartin

#20
Hi Den,

as I understand it your charger is connected to other devices through the enclosure. The enclosure is connected to protective earth. That should be fine.
You have to ensure, that your applied parts are adequately isolated from the charger circuit.

A short description of my last sentence:
The goal of the 60601-1 is safety for the patient / operator even in single fault condition. In your case this is ensured by:
- Protective earth connected enclosure (1 MOP)
- Isolation from mains with 2 MOPP

Therefore the patient and operator are always safe:
One single fault condition could be that the PE is interrupted. There are still 2 MOP limiting the currents and voltage from mains to enclosure.

I hope this is clearer

Best regards,
Martin
 
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