What does "other APPLIED PARTS" mean in IEC 60601-1 ed 3.0 8.7.4.7 b)

Eamon

Involved In Discussions
#1
One sentence in IEC 60601-1 ed 3.0 8.7.4.7 b) reads:

For this measurement, non-PROTECTIVELY EARTHED metal ACCESSIBLE PARTS including PATIENT CONNECTIONS of other APPLIED PARTS (if present) are connected to earth.​

As I understand it, this is a test which is done when the patient connection under test is raised to mains voltage, simulating the fault condition where the patient contacts mains. The device should not contribute to the patient's electrocution by grounding the patient and completing the circuit.

The problem lies in the interpretation of "other" APPLIED PARTS. Clearly in the case of a biopotential measuring device (for example a multi-lead EKG machine) if each electrode were considered a distinct APPLIED PART, no such device could pass.

So, what is the rule for determining what constitutes an "other" APPLIED PART whose patient connection(s) must be grounded for the test? Is this defined anywhere in the standard?

Thanks in advance for any light shed on this question.

Eamon
 

Pads38

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Trusted
#2
In your example of a multi-way ECG lead, all the leads are considered to be one applied part.

(That is for type BF parts - IIRC type CF are dealt with differently).

If you consider a multi-function monitor then the ECG leads form one applied part and then (for example) a blood pressure transducer would be another applied part. So any metal parts of that applied part should be earthed during the 8.7.4.7(b) test.
 

Eamon

Involved In Discussions
#4
Hello, thanks for the two answers.

Subsection g) is helpful in suggesting what they are talking about (referring to multiple functions), although b) is the one I'm concerned about.

In any case, we are just pushing back the definition. I guess I would need to know how to determine what a distinct "function" is.

In contrast to many medical devices which have a very specific purpose, we sell general purpose platforms with multiple channels that can be configured for different electrophysiological signal types. The application is research and biofeedback.

One application might require a configuration with two channels of EEG, two EMG, and one ECG to pick up heart rate. Another could require five channels of EEG. There is no apparent reason why risk arising from lack of inter-channel isolation would be any greater in the first case than in the second.

Cost to isolate each channel from other channels is prohibitive for this product's market, and I am reasonably certain our competitors do not isolate between channels. A couple of generations of this type of equipment (without inter-channel isolation) have been certified under 2nd edition and the next generation will be 3rd edition. Assuming a parallel provision as 8.7.4.7 b) exists in the 2nd edition, our testing lab has never interpreted this to require inter-channel isolation. However this time around we are reading the standard more carefully rather than just sending it off to be tested.

Now that I have given more detail on the device, I am wondering if someone would like to venture a more specific opinion.

All the best,

Eamon
 

Pads38

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Trusted
#5
I would suggest that all of the examples given are "amplification of a bio-potential" therefore one function therefore one applied part.

The seperation into ECG, EEG, EMG etc is largely a function of the subsequent signal processing rather than the isolation.

As I said before this applies to a type BF applied part. Direct cardiac connection - which would imply type CF - would be different.
 

wally4u

Starting to get Involved
#6
Have you considered the risk of one device actually being used on two people at the same time? I know in Asia they actually hook up multiple people to treament devices that support independent operation of biostimulation channels.

IMO, you are describing a BF device with multiple independent channels requiring isolation.
 

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