Determining Critical Components for conformity with IEC 60601-1

[DENich]

Hello all.
I'd like to discuss issues related with WORKING VOLTAGE and critical components.

A Notified Body demands filled-in CDF form (critical component list). A representative of the Notified Body claims:
1. Critical Component: A component and/or sub assembly identified during a product evaluation deemed to have an impact on the safe operation or safety features of a product as dictated by the applied standard(s). This can be an electrical, mechanical, or structural component.
2. Components under dangerous voltage (greater than 42,4 V peak a.c. or 60 V d.c) are critical components.

My understanding in terms of electronics is different:
1. The limits of TOUCH CURRENT, PATIENT LEAKAGE CURRENT and PATIENT AUXILIARY CURRENT should not be exceeded for APPLIED PARTS and ACCESSIBLE PARTS in NORMAL CONDITION and SINGLE FAULT CONDITION [refer to 60601-1 rev.3.0 par. 8.1 and par. 8.4]
2. ME devices should have 2 MOP to prevent APPLIED and ACCESSIBLE PARTS from exceeding the limits I specified in item 1. [refer to 60601-1 rev.3.0 par. 8.5.1.1]
3. A corresponded MOP is determined by WORKING VOLTAGE where WORKING VOLTAGE is the highest voltage between separated by the MOP parts which is possible within input rated voltage (refer to 60601-1 rev.3.0 par. 8.5.4).
3.NORMAL CONDITION includes short circuit of any insulation that does not comply with the requirements for MOP[ refer to 60601-1 rev.3.0 par. 8.1 a) ]

From the all above I conclude that if short circuit of a component can lead to increasing of the proper WORKING VOLTAGE we should consider this component as Critical. If short circuit of a component doesn't lead to a HAZARDOUS SITUATION I don't need to consider it as Critical component.

Actually there is not such a thing as Critical Component in 60601-1 at all. I have managed to find only one reference related with Critical parts in IEC TR 62354 (describes testing procedures for medical equipment). It claims Notified bodies should demand a list of safety-rlated components which should include components used in mains, means of protection, critical materials, internal wires.

So, what do you think I should do? Should I just obey to demands of the Notified Body and include to Critical part list all components under voltage greater than 42,4Vpeak a.c./60 V d.c? Since we have great amount of such components it will lead to non-flexible purchasing and strong dependence from different manufacturers.
What do you think TR 62354 means by "parts used in mains"? Are they components on the SUPPLY MAINS side of any mains fuse?
Could you share your own experience of filling in Critical part list and dealing with Notified Bodies on this subject?

Regards,
Den.

 

[siping21c]

Hi DENich

I have similar question too. What I generally include in critical component list are:

1. Any insulation providing MOP. This is because failure of the insulation will directly lead failure in limiting leakage current. The components including PCB board, isolation transformer, enclosure....

2. Any high-integrity component.

Let's wait for other's advice


Best regards,

 

[shimonv]

Hi DENich,
I would request kindly from the notified body representative to tell you where he got his definition from.
I could not find a clear definition for critical component in the 60601 standards family. It makes senses because the criticality of a component dependent greatly on the device intended use, design considerations, and operating conditions.
Critical components should be identified by means of risk-based approach.

If you follow bad advise you will find yourself frequently visiting the test lab for additional unnecessary and expensive tests.

-Shimon

 

[Thukira]

To your point that "it will lead to non-flexible purchasing and strong dependence from different manufacturers."

You can always justify through statement of compliance between the components to make as interchangeable item in CCL table of TRF by comparing the Power, current, load, wiring details etc is same and there will not be any impact on IEC testing/product risk, classification etc.

 

[Pads38]

As previously stated 60601-1 does not refer to 'Critical Components'. The requirement to create a list of such parts is driven, not by the Notified Body, but the test houses using the standardised Test Report Forms - which have a section to fill-in.

I have created an 'in-house' test capability for 60601-1 and have also used the services of external 'CB' test houses.

For my internal reports I do create a list of critical components and then provide copies of data sheets and certification for these parts. The third party reports are similar - but they tend to demand more parts to be listed. Many of these additions tend to be as a result of the need to prove flammability ratings.

For my internal reports I list -
(note here that the 'mental' example I am using is an old fashioned linear supply unit - switch modes make it less clear).

Parts in the mains supply circuit -
Appliance coupler
fuses and holder
voltage selector
switch
mains wiring (tri-rated)and any supplementary sleeving
mains filter / X or Y capacitors
mains transformer
mains lead - but that tends to be country specific

Other parts shown on the Insulation Diagram -
Opto-couplers
transformers with an isolation function
any other component with a safety function (can include relays, capacitors -depends on your device).
Batteries (not coin cells - but definitely needed for Li packs)

Other parts that I would expect an external test house to require -
PCB / PWB
enclosure material (particularly if polymeric)
materials of all other internal wiring and internal connectors

To provide all the information required I have found that having a 'UL' number is invaluable - it allows rapid and easy 'proof' to be gathered.

 

[DENich]

.

.

Hi Siping21c and Shimon. Many thanks for your opinions and advises.

You can always justify through statement of compliance between the components to make as interchangeable item in CCL table of TRF

Hi Thukira, great thank you for the advise. If I understand you correctly you advise me to specify 2-3 alternate (equivalent) components for each position in CCL where it is possible. Am I right? Are there any easy ways to change a critical component in a device which have already been certified?

I have created an 'in-house' test capability for 60601-1 and have also used the services of external 'CB' test houses.

Hi Pads38, Great thank you for the detailed report. Unfortunately, I'm not sure I understand what "'in-house' test capability" and " services of external 'CB' test houses" you speak about. Do you mean you have special algorithm for determining critical components?

In my opinion, Risk analysis based on examination applicable HAZARDOUS SITUATION (IEC 60601-1 ed. 3.1 par. 13 and ISO 14971 ed. 2 Annex C) should be conducted. If it is admitted that deviations of parameters of a component can lead to HAZARDOUS SITUATION, therefore this component should be classified as Critical one.

I'm still not sure how to handle WORKING VOLTAGE. Should I consider a real potential difference under conditions of NORMAL USE or should I examine any possible malfunction of any component clearance, creepage, insulation which are not MOP and try to evaluate the maximum possible potential difference during this malfunctioning? If we accept this conception, I believe, we should worry only about components forming MOPs and classify only these components as Critical ones.

I'm in two minds.

Regards, DEN.

 

[Thukira]

Hi Denich

You can make "N" of components as interchangeable without any additional testing provided the current, power, voltage, ie. electrical load, component level certification requirements, electrical wiring in end product were same for all interchangeable items.., to ensure that there is no impact on emc/I, electrical safety tests..as result testing will be performed on one component and make others as interchangeable in your CCL table.

 

[DENich]

Hi Thukira,
Thanks for the explaining. It's really good advice.
Regards,
Den.

 

[Thukira]

Your Most Welcome, Den!

In case if you want to amend the TRF for any change in model when there is no impact on previous test results; still go you can for it..

https://www.iecee.org/documents/refdocs/downloads/od-2020_ed.3.1.pdf

Refer Section 5.4 Amendment Report Example

From: IECEE OPERATIONAL DOCUMENT - IEC System of Conformity Assessment Schemes for Electrotechnical Equipment and Components (IECEE System)
TRF – Development, maintenance and use

This is the guidance for any NB to follow.

 

[DENich]

Hi Thukira,
Great thanks again
I'll keep this in mind.
Perhaps, you could tell me how costly a procedure of adding amendment to a TRF is in comparison with cost of the first time CB tests and how much time it may take (let's assume I want to add a new critical component or substitute already specified in a CCL component)?
Regards,
Den.