Is any part of earthed (grounded) enclosure required to meet, say, 25A/0.1ohm?

[Roland chung]

Yes, the standard is quite clear on this point.

The case is that one part of the upper cover failed the impedance test. But the MAINS PARTS locate inside the lower cover. Since the cover is integrative, could you tell me how to conduct the Hi-Pot test for the upper cover to avoid the high voltage to stress the protectively earthed parts (i.e. lower cover)?

 

[Peter Selvey]

There should be no need to do a hi-pot test on the cover, just because it failed the 0.1 ohm test.

Did you check 17 g 3) of the 2nd edition? I think this applies to your case:

Mains -> Basic insulation -> PE part (0.1 ohm) -> E part (>0.1 ohm)

For the last part we don't care, because PE part is in between.

 

[Roland chung]

I absolutely agree with you. The Hi-Pot test is not necessary at all and such parts also need not to be subject to 25A test based on the engineering judgement.

17 g)3) is a good statement but has been deleted in the 3rd ED.

 

[Marcelo]

I think it is not true. The barrier between pri and sec is double insulation already. There is no hazardous voltage around such earthed accessible part (SELV only), why 2 MOP is needed?

The problem is really not the hazard voltage at normal condition, but in SFC. The construction of the protection of electrical shock is clear - you need 2 MOP, one for protection under normal condition, and another, for protection at SFC (this is not really explained in 60601, you need to read for example IEC 61140). One way is Basic + protective earthing, if not that you need another way to have to MOP. But your are correct, IF there´s double insulation between primary and secondary (and not only the transformer, of all parts) this means that you will have double from the parts you mentioned.

Parts which are only 1 MOP from mains parts should be earthed with 0.1ohm. Parts which are 2 MOP (or more) don't need to be earthed.

Not really on the first case. Parts with only one MOP can have another MOP (supplementary) forming parts of a double, or being protected by an earthed internal screening. However, the need for two MOP is still there.

I think the main problem is the construction of the insulation system, as created BY THE MANUFACTURER. In Brazil we have a real problem in which manufacturers do not provide insulation diagrams, so it´s really difficult to perform the correct tests without testing wrong insulation (or not testing earthed parts, in this case)

But a biomed should not be trying to re-test 601 in the hospital.

Another historical problem.

One way is to point out IEC 62353 as the way to perform post-market safety testing.

 

[Marcelo]

why do you not allow to conduct the 2 MOP Hi-Pot test for parts can not meet the 0.1ohm

Parts which do not pass the 0.1ohm are not protectively earthed and cannot be counted as 1 MOP. You have to provide another way to have 2 MOPs for them, that´s what I commented earlier.

17 g)3) is a good statement but has been deleted in the 3rd ED.

Not, is was not deleted, only moved to the explanatory annex, so there would be no restriction on the ways 2 MOPs could be created (in the second edition you could only use the 5 ways). See the rationale for 8.5.1.

 

[Roland chung]

Not, is was not deleted, only moved to the explanatory annex, so there would be no restriction on the ways 2 MOPs could be created (in the second edition you could only use the 5 ways). See the rationale for 8.5.1.

I am sure that 17 g)3) has been deleted in 3rd ED. Please refer to IEC/ TR 62348 and also subclause 8.5.1 in annex A.

 

[Marcelo]

I am sure that 17 g)3) has been deleted in 3rd ED. Please refer to IEC/ TR 62348 and also subclause 8.5.1 in annex A.

Not deleted, but now there's a comment there's no recognition anymore to using the third option (3) of the second edition due to problems.

As I said before, see the rationale the rationale for 8.5.1.

 

[Agust Sigurdsson]

This has turned out as a very informative thread for me regarding an issue of the PE-connections of a device which we want to power from a ready made in-line power supply which is itself PE-connected but has no provision for us to connect our device to the PE conductor.
If someone of the experienced persons who have been contributing to this thread would please take a look and comment on my thread I would be very pleased.
Unfortunately I am not allowed (yet) to post a link to my thread, but it has a reference number ...t=59815. Hope that will not be censored too

Thanks.

Agust

 

[Agust Sigurdsson]

This has turned out as a very informative thread for me regarding an issue of the PE-connections of a device which we want to power from a ready made in-line power supply which is itself PE-connected but has no provision for us to connect our device to the PE conductor.
If someone of the experienced persons who have been contributing to this thread would please take a look and comment on my thread I would be very pleased.
Unfortunately I am not allowed (yet) to post a link to my thread, but it has a reference number ...t=59815. Hope that will not be censored too

Thanks.

Agust

... Sorry if I am generating too much noise, but probably I ****ed up the reference to the thread. It can for sure be found if searching for "Medical Device Protective Earth (PE) issues"

Agust