EBME Forums Forums Maintenance Technical Assistance EN 60601 neutral/earth connection?

I think the IEC60601 regulation is changing next year. Check what edition you will be designing, building and testing too, as this might all change.

A.M

Hi Mr Ling

For the dielectric strength tests, BS EN60601 requires a higher flash test voltage than standard double wound isolation transformers.

60601 clause 57.9
61558 clause 18

Also the creepage and clearance requirements are greater in 60601.

60601 clause 57.9
61558 clause 26

I hope this helps.

Thanks.

IEC60989:1991 Seperating transformers, autotransformers, variable transformers and reactors is mentioned as a normative reference in 60601-1-1. The "3rd" edition standard of 60601-1 is currently available to the public as a draft proposed standard for comment: 00/565498DC BS IEC 60601-1. Medical electrical equipment. General requirements for safety and essential performance .

"...But I still can't find it written in the 60601 standard that the output from a isolating supply transformer must be floating (that would make my life so much easier!!)."...

Morgan

You won´t find what you want in the body of the standard because it´s a standard for "medical electrical equipment", not a standard for "medical electrical equipment with isolating transformer". I means that the isolating transformer is an option, and it means therefore that the secondary could be earthed in principle. However, as stated before, depending on the construction of the equipment (or system, or wherever) the tests will fail if the secondary is earthed. The best example, i think, is a floating (BF or CF) applied part. This floating means floating from earth, because if it´s connected to a earthed part and you perform the "mains on applied part" leakage current test (which is the test that determines if the applied part is really floating) the leakage current will be more than the limit and therefore the test will fail. This rationale can be found in a standard, but not in IEC 60601-1. You can found it in an annex (Annex A i think) of IEC 60513 Ed 2 - Fundamental Aspects of Safety Standards for Medical Electrical Equipment.

Hi Mantunes,

Actually these comments appear very misleading to me.

I just want to say that seperating transformers are not used to correct earth faults nor limit the leakage between applied parts to all of the BF/CF requirements of 60601-1.

Hello Mr Lig

The example i cited is the only one i remenber can be traced to a normative document. Surely, there´s more examples cited in IEC closed documents (i remember some from the comments on drafts of the third edition of IEC 60601-1) but they´re not normative docs. The

Also, the statement "just want to say that seperating transformers are not used to correct earth faults nor limit the leakage between applied parts to all of the BF/CF requirements of 60601-1" is in gereral right, but separating transformers are differente from isolating transformers. Separating doens´t necessarily means isolated from earth, but isolating means separated from earth.

That is why I made the statement.

Hum, so i think i didn´t understand what you said about the comment being misleading, as my comment was on isolating transformers and not on separating ones.

If you connect a floating applied part (the bit that connects to the patient) to earth the applied part is still isolated via the instrument - the test fails because you're applying earth-referenced mains direct to to earth, not testing the isolation of the applied part.

In practice leakage would not flow through the patient via the instrument connected to that applied part. The fault-current or "leakage" is actually bypassing the applied part connected to the patient and flowing to earth - you've made an external circuit.

Otherwise you must be talking about earthing of applied parts inside the DUT - which in that case they wouldn't meet the BF or CF requirements in the first place. Where do you mean connected to earth - internally or externally?

If a device using an external isolation or seperating transformer, for that matter, is used and the applied part is earthed then tested with earth-referenced mains on the applied part test, you still end up with the same result - a fail and excessive current flowing through the connection to earth.

I don't think it was a very good example to use, that's all, irrespective of the degree of electrical isolation being discussed.

You are totally right in what you say, but that´s not what i was traying to show. I surely wasn´t clear in my statement anyway. What i was trying to say is that earthing th secondary depends on the application, in this case, in which type o applied part the equipment will have. In this case, if the manufacturer says it´s BF or CF but it´s connected to an earthed secondary the tests will fail (as you kindly pointed out). I agree that´s not the best example, but it happens a lot in my laboratory. And, besides, it´s the only that i remember that is written on a standard, and it seemed to me that´s what the original poster wanted when he talked about the "i think...' or "in my opinion.." posts.