External power supplies: How close does the safety report have to match the end-use application?

#1
Hi all,

First off, I wish I could contribute to this community in a better way, and not just ask a bunch of questions. Unfortunately, I just don't have the experience (yet) to confidently give feedback/advice. That aside...

I work for a power supply manufacturer. A large percentage of our customers are medical. Since my ex-boss left, it's been up to me to work through a lot of the regulatory related issues.

Our medical power supplies are tested according to IEC60601 by Intertek typically. It was my understanding that a safety report for an "off-the-shelf" power supply is "generic", and that the manufacturer of the final system is responsible for certification of the completed system. But, at the same time, I don't think the power supply would be completley re-tested in the final system. So, to what extent does the power supply's IEC60601 report get used in a final system's safety certification?

A real example: We have a customer with a system that draws power according to a "pulsed-load" profile. That is, it has a quiescent idle state, then transitions into a momentary high power mode, then returns to quiescent. They suggest that the power supply should be tested according to this profile in our IEC60601 report. Does this make sense?

If that power supply has a nameplate rated power of 100W (on the safety report), but the end-use system draws up to 150W in short bursts, while maintaining an average <100W, is this acceptable in the end-use system? Does the manufacturer of that system have to provide an justification as to why that's OK?

Sorry for so many questions. If anyone has answers to any, I'd really appreciate it. As you can tell, I'm feeling a bit overwhelmed.

Thanks,
Tim
 
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Benjamin Weber

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#2
Hi Tim,

contribution is not only answering, but also asking the important questions ;-)

First of all: A power supply usually is not directly in the scope of 60601-1 since it is not a medical device on its own. It does not have a medical intended use. But there are a lot of requirements regarding the power supply of the ME equipment. Therefore a power supply for ME equipment can only be tested to certain parts of 60601-1.

The manufacturer of the final ME equipment is responsible for compliance with the end product standard/s (e.g. if he decides to show compliance with the essential requirements of MDD/MDR by this way). If the requirements that aim at the power supply are already passed by your test reports, the manufacturer has a good starting point. But there might still be some requirements, that you cannot test on the power supply alone, but the manufacturer has to test in the final device. Some examples may be labeling, fuses, fire prevention. The test report should explicitly say, whoich requirements of the standard were tested. Usually such partial test report contain a statement about the requirements, that the manufacturer of the final end product is responsible for. In CB scheme test report these are the so called "conditions of applicability".

Regarding the rated power input: Your power supply has a given rating of 100 W. As long as there is no other information, this is the maximum steady-state value within the rated supply voltage range/limits (IEC 60601-1:2012, cl. 4.11). Yet the labeling depends on the type of power input (IEC 60601-1:2012, cl. 7.2.7): If there is a momentary peak power input this shall be labelled in addition to the long-term value as described before.

I guess the power supply should be considered a so-called "critical component" of the final device. According to cl. 4.8 such components shall not be operated outside there ratings. Your power supply is rated for 100 W only, so drawing 150 W (also for short terms only) I would consider to be out of the rating and the manufacturer of the final device is responsible for showing, that operating the power supply at 150 W for short terms does not result in an unacceptable risk (excessive temperatures, fire, deteoration of solid insultion and as a result electrical shock are only a few to name here).

The manufacturer of course can ask you, to show 60601-1 compliance when 150 W are drawn from the power supply. But you are not obliged to do this. You have to evaluate if the efforts for retesting at this rating are acceptable for your company. In the end you may sue the result for generally marketing your power supply? Or is this so special, that it is only relevant for this one manufacturer? You can also try to negotiate about splitting the costs for this retesting? But these are more or less only commercial aspects.
 
#3
Thank you Benjamin for your reply. The good thing about the internet is that everyone gets to see your "dumb" questions, so I suppose it's contributing in some way.

So, while the end product manufacturer is responsible for ensuring the entire system is in compliance, they may use the power supply manufacturer's partial test report to demonstrate compliance in the applicable areas? I assume the closer the power supply manufacturer's partial report matches the end use, the less re-validation the end product manufacturer has to do.

The power supply in question is slated to be part of our standard product line (with many voltages/options), but it has not yet went through IEC60601 testing. This power supply was developed with input from one of our medical customers who intends to buy the power supply once certified. Since IEC60601 testing hasn't started yet, we are considering including the medical customer's peak loading conditions for their model in the family CB report.

Can we ask Intertek (or another agency) to confirm compliance at a certain test condition for a limited scope of the product family? Would we state the customer's specific conditions in the "conditions of applicability"?

Thanks again for your help!

Tim
 

Benjamin Weber

Trusted Information Resource
#4
If you test the power supply at the conditions your customer requires and it passes the relevant tests, I think you could state this in the ratings of the power supply, not in the CoA. The conditions of applicability mostly relate to limitions of the comformity assessment by the test lab.

For example:
- 60601-1 requires certain information to be disclosed in the instructions for use that relate to the power supply of the medical device. This may be disclosure of residul risks, which highly depend on the way the manufacturer implements hte power supply and the surrounding components. This information cannot be identified during testing of the power supply itself. So the test report of the power supply may contain the information, that there may be information to be disclosed in the IfU of the end product.
- Maybe the power supply is allowed to be built only a certain position, so that the venting is not blocked. The CoA then would contain a statement, that the power supply chall only be placed in the intended position and that the temperatures have to be tested within the final device.

If you have a good specification from your customer regarding the peak power input (e.g. maximum time for peak power input, minimum time for recovery, maybe expressed as a duty cycle), you should get in touch with the test lab and discuss directly with them, how this condition would be considered during the tests and how this could be expressed in the test report, if this specification is applicable only for a part of the product family.
 
#5
Thanks again Benjamin. I think I understand the idea behind CoA now. They are the conditions that must be met in order for the data in the report to remain valid. So putting the loading profile in there just doesn't really make sense.

I think you're right. I ultimately have to get in touch with the test lab. Unfortunately, English is not the primary language used at our test lab so it can be quite challenging to try to relay this information. But, that's not your problem!

Thanks again!
 
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