EBME Forums Forums Maintenance Technical Assistance How should we test stacks?

Perhaps I can throw a little light on some of these issues.

First, the latest definition of a Medical Electrical System (from IEC60601-1:2005) is a “combination, as specified by its MANUFACTURER, of items of equipment, at least one of which is ME (medical electrical) EQUIPMENT to be inter-connected by FUNCTIONAL CONNECTION or by use of a MULTIPLE-SOCKET OUTLET”. (Sorry about all the capitals – they use them in the standards where a word or phrase has a definition in the same standard). Incidentally, by definition, if you have assembled the system, that makes you the MANUFACTURER! So there you go – that makes most “stack systems” ME Systems, so no need to differentiate for the purposes of electrical safety testing.

Second, what is this “new electrical safety testing regime that has been agreed”? The only one I know of is the new International Standard agreed by the International Electrotechnical Commission (IEC) and published last month. This is IEC 62353 – “Medical electrical equipment – Recurrent test and test after repair of medical electrical equipment”. I think the UK members of the working group voted against it, but its out anyway. See www.iec.ch/searchpub for details. Unlike IEC 60601-1 that is intended for “type testing” only, IEC 62353 is intended for routine testing of equipment in service that has been manufactured to comply to IEC 60601. I asked the MHRA what their line on it was going to be and, basically, they don’t have one at present.

However, IEC 62353 does have a line on testing Medical Electrical Systems. Under “General requirements” that apply to tests before putting into service, recurrent tests and tests after repair, it states that “Each individual equipment of an ME SYSTEM which has its own connection to SUPPLY MAINS, or which can be disconnected/connected from SUPPLY MAINS without the use of a tool, shall be tested individually. Additionally the ME SYSTEM as a whole shall be tested to avoid a situation where aging of individual equipment can result in unacceptable values.” So, its saying do both! The standard gives values for leakage currents that are common to both individual items of medical electrical equipment and to medical electrical systems. A particular value for protective earth resistance of medical electrical systems distinct from that for single items of medical electrical equipment is specified.

And, just in case you were wondering, yes the new standard is covered on Eastwood Park’s Safety Testing of Medical Electrical Equipment course and on other courses where the general topic is addressed.

Welcome to the forum, Vaughan. Your contribution is well over-due. Don’t worry about Richard, he gives everybody a hard time (especially me). Let's have more from the guru of electrical safety!

As I've said before, I don't see why we should need to interpret standards. They should already be clear and concise, and written in plain English for all technicians to follow. Blokes carrying out routine electrical safety tests shouldn't need to hold opinions. It should be "Monkey see, Monkey do", eh Vaughan?

Thanks for your welcome Geoff – hope you’re well!

I don’t agree with the thrust of your last point. Perhaps it would be nice if standards were written in straightforward, concise easy to follow fashion, but in general they are not (for various reasons). In practice, I think that, whatever guidance people are following when performing tests on medical equipment, judgements need to be made based on extensive knowledge and experience. I am pleased to see this view explicitly supported in the new IEC 62353 which states, again under “General requirements” that “Qualified personnel shall perform these tests. Qualification shall include training on the subject, knowledge, experience and acquaintance with the relevant technologies, standards and local regulations. The personnel assessing the safety shall be able to recognize possible consequences and risks arising from non-conforming equipment.” (By the way, this is a direct quote, not a paraphrase.)

No disrespect to monkeys – but I don’t think this falls within their skill set!

Shame 62353 isn't applicable yet isn't it?

Hi Richard,

As far as I'm aware you can mix and match safety testing in the UK (as is the case at the moment) as long as you back it up with reason and expertise (ie risk assessment). IEC 62353 can be applied just as any other "guideline" applicable in the UK. Rigekl supply a free guidance booklet on the new IEC 62353. (free from www.rigelmedical.com).
Most hospitals who do not test to MDA or IPEM guidelines use either their own test guidelines (ie no testing on Class 2 equipment or visual testing only)or pick and mix from the IEC 60601-1 (ie no F-type testing, No Dielectric testing, no SIP/SOP testing, 2 sec earthbond test instead of 10-60 secs) because some tests are deemed destructive to the EUT (read; time consuming and impractical).

So why not adopt a standard that will be used (specified in the service manuals) by most of the manufacturers within the next 12-24 months? That makes it applicable to me.

Oh yes! "Pick 'n' Mix", and "Mix and Match" our way to excellence in biomedical engineering. That sounds like the route to lifting the profession to new heights, eh John?

If most hospitals do not follow the guidelines, what’s the point in having guidelines at all?

Yes, we need sensible, practical standards, that everyone at first-line can buy in to. That is, not manufacturing type tests, but simple and effective tests to be carried out during routine servicing.

But we’re back to the same old question of "who sets the standard"? Perhaps it should be us, right here. As Vaughan mentioned above, the international pundits can’t even agree the academic issues (so why even listen to them?).

So, come on then guys, let’s have the debate (yet again). Let’s draft our own checklists (I won’t use the word standard) aimed at routine electrical safety testing of all types of medical equipment normally encountered. I’m talking about practical application here, not the song and dance and minutae of the banal utterings from the Gods. Quick and simple tests aimed at ensuring electrical safety is what it’s all about.

Leave the boffins to their dreaming spires, and let us hands-on people get on with the work, secure in the knowledge that we’re following accepted best practice (agreed by our peers), and will be supported in case of dispute (should any such thing ever arise)!

Will this happen in my lifetime? Somehow I doubt it!

Yes I agree with your comments to some extent John and it is possible to "pick and mix" tests for manufacturing and justify your decisions but for routine testing, i.e. regular testing using a safety tester with standard-limits and tests built-in by the safety tester manufacturer, this is rarely the case in practise.

"Mixing and matching" of safety tests is neither consistent nor considered applicable for most of us that rely on limts established by currently recognised standards e.g. 60601-1. This is because the advice or assistance from the MHRA does not refer to anything other than 60601-1 and certainly not "mixing and matching".

I say that in future we will be justified in applying both standards, either 60601-1 or 62353 depending upon whether we're manufacturing in-house, acceptance testing or carrying out routine testing, respectively. The application is the main issue.

Considering 62353 we need to know whether, currently, BSI, MHRA or the professional institutions have any issues with its application. I am surprised, with your involvement with the 62353 standard, John, that you are implying "mixing and matching" of tests required in standards that are intended for different purposes, i.e. either type-testing or recurrent safety testing.

Promoting risk assessment to influence testing methods using a standard that is not currently ratified by the BSI is not a good basis for applying safety testing regimes in the UK in my opinion. I would prefer to rely upon advice from independent sources, the regulating bodies, professional institutions, standards bodies, etc and wait until 60601-1 is officially and publicly deemed inappropriate for routine testing and 62353 is considered applicable for this.

Meanwhile, personally speaking, I would prefer not to take a significant decision on my shoulders about which standard to apply, or not, if there's a possibility that the requirements, or application of the standards are in conflict and one isn't not actually "current".

60601-1 is the de-facto standard applied by manufacturers and us at the moment - the issue being the application of tests that are not deemed relevant to us, not the limits for earth-bond, leakages, etc, that have been decided upon.

Mixing and matching tests required in these two standards is not appropriate for us since the intention is that they apply under different circumstances. My opinion has always been that a more prescriptive standard, applicable to routine testing rather than safety testing, with safety testing rationales, etc, such as 62353, has been needed for a long time, i.e. I'm in favour of such a standard.

However, personally speaking, I'd prefer its introduction to be promoted and guidance on its use to be provided by professional institutions and standards bodies, etc, rather than those with vested interested, e.g. safety tester companies & those involved on the specific standards comittee plus those selling 62353 training, relying on it becoming the de-facto standard before BSI "sign up to it" if it's "pushed".

What I'm saying is that I'd prefer customer "pull" for the standard, services and products that will spring up around 62353, rather than supplier "push" to force it on us without the BSI, MHRA, Empoyers, HSE, etc, feedback first. The guidance from the standards and legislation should do this, not some company or those with vested interests "forcing" it on us.

As soon as the 62353 standard is harmonised/ratified by the BSI then I will be inclined and obliged, in fact, depending upon what the guidance is from the MHRA and my employer's requirements, to apply the 62353 tests, rather than the 60601-1 type-tests when doing recurrent testing, etc.

Meanwhile, since it's neither harmonised/ratified by BS, I believe, I will continue testing to the de-facto standards that exist for manufacturers - as I am of the opinion that the ones I carry out, using a medical grade safety tester with built-in tests and limits, are applicable for routine testing. Using the tests that medical electrical safety tester manufacturers, including Rigel, have previously configured them for before IEC62353 was introduced, in fact.

My personal preference is to wait until the standard becomes a British/EU standard or is harmonised. This means that the BSI will have released a standard that the institution is happy with and one that is applicable to us. I have no vested interest in either providing training or selling products that involve 62353 or 60601-1 and I can, generally speaking, interpret and apply published standards that require tests to be performed.

This waffle aside, irrespective of the "standards" that are applied, the equipment goes out of the door "safe".