Class II Medical Device Marking - Different IEC 60950 & IEC 60601 Requirements

[Roland chung]

Hello forums,

In IEC 60601-1, Class II equipment with functional earth (e.g. internal screen for EMC purpose) should also mark a Class II symbol on the label.
However, the same construction is forbidden to mark with Class II symbol in IEC 60950 (see clause 2.6.2 for details).

Would it be a problem when such a 60950 compliant equipment became an item of ME system?

Regards,
Roland

 

[Stijloor]

A Quick Bump!

Can someone help?

Thank you very much!!

 

[ca_moni]

Our notified body , many years ago, refused to accept a label with the class II mark and we had to remove it.
The device was class II, but it was powered by a commercial (medical grade) power adapter on which the connection to earth was used for the EMC screen. The output of the power adapter was a two-pole concentric connector, so no way that there were a protective earthing of the device: nevertheless, they stated (in brief): "If there are three pins in the mains plug, then it is a class I".

 

[Roland chung]

Thank you for sharing experience.

It seems IEC 60601-1 is clear to the classification of equipment with functional earth. It is reasonable to classify such equipment to Class II, because of the equipment does not rely on basic insulation plus protective earthing for protection against electric shock.

 

[Peter Selvey]

ca_moni mentioned:

The device was class II, but it was powered by a commercial (medical grade) power adapter on which the connection to earth was used for the EMC screen.

I would be suspicious in this case. In 25 years I have seen a couple of cases of Class II equipment with a functional earth, which is then confirmed to have 4kV/8mm spacing from mains parts as required in IEC 60601-1. But these had custom designed power supplies, not off the shelf. I never saw an off the shelf Class II "Medical grade" power supply with a functional earth. I expect it not to be commercially viable because the application is rare, and the potential for confusion is also high.

For the original question, I think it is not an issue in terms of compatibility with IEC 60601-1.

A device labelled as Class I (i.e. no double box symbol) but has all internal earth connections double insulated from mains parts (8mm/4kV) and only used for functional purpose still complies with IEC 60601-1. While unusual, there is no point of non-compliance in the standard, and no safety issues.

Also, this is the best option. The potential confusion from labelling a 3 pin device as Class II is not worth it. If the earth is used only for EMC, then it still needs to be connected to earth anyway to comply with regulations. The user does not know the internal construction so it makes no difference to them if the internal earthing is functional or protective.

 

[Roland chung]

Thank you for your opinion.

We actually have an equipment with functional earth only. The equipment is enclosed by plastic. Yes, it is indeed a 3 pins device. But the earth conductor in the power supply cord is directly connected to the interior coated surface which made for EMC purposes.

If such equipment is classified as Class I, it really conflicts with the definition and clause 8.6.9.

 

[Peter Selvey]

Clause 8.6.9 would be not applicable if the equipment is classified as Class I. So, it's not a problem.

The only I see would be the definition:

3.95 PROTECTIVE EARTH TERMINAL
terminal connected to conductive parts of CLASS I equipment for safety purposes. This terminal is intended to be connected to an external protective earthing system by a PROTECTIVE EARTH CONDUCTOR

Some people might say if there is no safety related connections then the terminal cannot be called a protective earth terminal. But even the metal parts of the terminal itself (e.g. the end of an appliance inlet that extends inside the equipment, or the terminal block for connecting the cord) should be considered an internal connection.

Also, looking at the definitions and requirements in the standard, in particular figure 4, it may be that a functional earth terminal is different to the pin in the appliance inlet or terminal for L/N/E cord connection. So the NB's original comment may be correct (3 pin device must be Class I).

 

[Roland chung]

So, you meant the protective earth connection in my case is only from the pin of plug to pin of appliance inlet, the functional earth connection is from pin of appliance inlet to interior coated surface.

So, the 25A/0.1 ohm test can be performed, but only between the pin of plug and pin of appliance inlet.

If it is ture, the concept of Class II equipment with functional earth (clause 8.6.9) becomes superfluous.

 

[Peter Selvey]

This is actually new for me, but reading the standard again, it appears that Class II equipment can have a functional earth terminal, but that terminal is not part of the mains supply connection. It appears to be a separate terminal somewhere on the outside of the equipment. Figure 4 shows the terminal well apart from the mains supply connection. Also, it is nowhere written that the "functional earth terminal" can use the supply mains terminals, it's just something we assumed.

In this case, 8.6.9 is still useful (not superfluous).

Note there is a difference here between "functional earth terminal" and "functional earth connection". It is OK to connect to the protective earth terminal for functional purpose (this is very common). But in that case, the equipment must be Class I. If the functional part is not tested for 0.1ohm / 25A, it needs to be double insulated. 8.6.9 does not apply, because it is not Class II.

 

[Roland chung]

Reading the clause 8.6.9 again, it is clear the third conductor of supply cord is used as functional earth connection. The situation described in the 8.6.9 is indeed a 3 pins device.

I think the Figure 4 does not necessarily correspond to clause 8.6.9. It is actually just an example.