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We have recently received 3 Criticare 506 N3 and whilst electrical safety testing as per our norm we discovered on these Class 1 CF devices that there is no protective earth terminal.

A phone call to the supplier suggested that they use a "breakout box" between the IUT and the mains lead. We pointed out that this tests only the lead and not the IUT - they agreed.

Further correspondence concluded with "I do not see a need for ground continuity testing as a part of your acceptance test for this particular product" claiming 60601-1 supports this.

What do you think?

Mick

I think that the "standards" being followed by most biomed departments have not kept pace with the reality of present-day equipment! If my memory serves me well, this bit of kit uses a "power-brick". Is the earth meant to be continuous all the way through the brick to the unit itself? I doubt it. I believe that we need to ask ourselves what, exactly, we are trying to achieve when carrying out EST on units such as these (and there are many such units, are there not)?

That is the old 506 Geoff. The new one (N3) has an IEC up to the monitor. They also originally claimed that we could test it as a Class II. However the earth leakage was 250uA. Well in excess of the 10uA.

Mick

Hi Mick,

Given that the 506N model is likely to be MDD risk classification IIa or IIb and Criticare operates a full quality assurance system, to my knowledge, then the route to conformity is likely to be down to the company "self-certifying" the product by issuing an EU certificate of conformance. At this stage the manufacturer obviously considers the device to comply.

If the relevant certificate(s) for the product refer to reference standards such as BS EN 60601-1 or equivalent harmonised standards, for example, then you could access these as a source of reference - if you think the lack of an accessible earth is an issue.

You could try to communicate your concerns to the regulatory affairs representative for Criticare in Europe or the US perhaps. Hopefully Criticare should be in a position to explain (or justify) the lack of an accessible earth. It's a shame that evaluation, prior to purchase, didn't pick up on this issue - suppliers seem more willing to discuss this sort of thing prior to purchase if they think sales are at risk.

Unless you have a solid argument that the lack of an accessible earth or evidence that seperation of mains from non-earthed metal accessible parts, if there are any, (including those within non-conducting enclosures not considered mechanically or electrically sound) means that earth protection is inadequate then I doubt if you'll be able to get support.

However if you're unhappy with the advice you've already received from Criticare or their agent and still have concerns about the product the regulatory people at the MHRA may be able to assist you and advise if necessary. Best to play safe if you're not familiar with the product.

As far as I'm aware the lack of an accessible earth is acceptable under circumstances that are indicated in the 60601-1 standard and its rationale. In these circumstances there is little more that can be done except to indicate a "non-accessible earth" perform the Class 1 safety test and then test the earth in the 3-core mains seperately.

As far as I interpret it: if there's adequate seperation between mains parts and accessible metal parts, under normal and single fault condition, then the accessible parts can be left floating or connected to a functional earth - otherwise, if there's not adequate seperation, any accessible mains parts need to be earthed.

You're probably best seeking advice from an expert at the MHRA.

If you look up the usser manual for the 506N3 you will see it is a Class 11 CF not Class 1 RTFM

That's strange - the technical literature I've seen indicates Class I CF. Admittedly I haven't seen a 506N3 up close.

If they are Class II CF, the units would fail acceptance checks immediately as the units are not marked as Class II on the device.

We have some in our trust, they are Class I CF and I test them to Class II CF with no problems. Lets face it, if there is no exposed metal parts which are earthed then all you need do is test the enclosure leakage.

The only real concern I have however is if there is any insulation breakdown over time as you cannot test this.

Does a standard Class II test on your safety tester measure earth leakage, patient leakage or patient auxillary leakage current, under earth O/C SFC JohnBhoy? Class II testing of Class I equipment with no accessible earthed parts means you could miss problems with conductive CF applied parts under earth SFC. I guess with the 506N3 there's no conductive patient applied parts to test, eh?

Not something I'd encourage when testing Class I devices with conductive applied parts and accessible earthed parts for sure - do people use Class II tests to overcome problems with Class I automated tests being interrupted if you can't connect to an accessible earthed part? I suspect some do - I'm just curious as to why you'd want to test Class I as Class II that's all.

I have just refered to the 506N3 user manual.
Under specifications - subsection Environmental it states:

Medical Device: Class II Equipment
Electrical Protection: Class I Equipment
Degree of Protection: TypeCF Defibrillator-Proof

Which can cause confusion. However I have interpreted this as a Class I device to be electrically tested to Class II EST standard (due to the no exposed metal parts and probable manufacturing build methods used.

As long as the device passes Class II CF EST and has not been obviously damaged, I really cannot see the real issue. This device Has been CE (0413)marked for conformity and states that the Leakage Current complies with leakage current limits required by medical safety standards for patient-connected devices. Standards include IEC601-1, 2nd edition, 1988 Part1.

I really do not see a problem testing this device to Class II CF EST standard.

As you've already said:

Thus they would fail since they're not marked Class2.

MDD (medical Device) classification is the risk classification, i.e. Class IIa or IIb as I interpret it. If it passes Class 2 EST as a Class 1 device then fine. However a class 2 EST on a safety tester does not necessarily fulfil all the leakage and isolation tests required for a Class 1, earth protected device (with or without accessible earth, i.e. a functional earth), with conductive applied B, BF or CF parts.

Class 2 assumes that there's no earth in normal or SFC conditions - thus some tests required to be performed on Class 1 devices are not performed in a Class 2 EST - test a Class 1 device to Class 2 and you'll miss tests on the patient applied parts and enclosure wrt earth (whether it's functional, protective, accessible or not). That's my interpretation.

As I posted earlier:

The CE mark and notified body number may refer to the total quality assurance route, i.e. quality and manufacturing for the product, not a type test (considering the product is MDD Class II). Someone needs to speak to the manufacturer and get it straightened out in my opinion.

I think you are right, but feel the MHRA should contact them not individual Hospitals. As a more definintive answer is required.

Classifying the device as Class I electrical, Class II medical has really set the cat amongst the pigeons and hence the confusion.

However what do you do in the meantime? reject the units outright or test them to Class II CF and wait for clarification.

To reject them outright would certainly spur Critcare into action but cause delays to the medical staff who just want to use them.

I will flag this issue again with our department head who used to work for the MHRA and see if he can take it forward. When I raised the issue initially with him, he made the final call on the products acceptance within the trust.

I see what you're getting at although I disagree that EST to Class 2 is acceptable when testing Class 1. Any of us, as technical representatives of the purchaser, are entitled to contact MHRA or manufacturers if we have a valid concern RE: technical or clinically related technical issues. MHRA don't know about these issues until we or the manufacturer contacts them - or there's an incident logged by the operators.

Check the PPQ for class designation, I assume class 1.

I would personally reject them and inform finance to stop payment.

Give the manufacturers 30 days to make an appropriate response rather than speculation and give them the opportunity to modify the devices if it is both appropriate and a certified modification (device has to be re-certified CE).

If they dont then they loose the business and I'm sure there are cost effective solutions other than that particular model.

That way, the manufacturers are running around rather than us poor hardworking EBME guys.

I took this issue up with Richard Mellish at the (then) MDA in early 2002 following receipt of two Tyco patient warmers which, at the time, were Class 1 items with no external accessible earthed parts whatever. Subsequently Tyco were considerate enough to begin fitting earthed studs to the units as an aid to hospital technicians.

Mr Mellish was and may still be chairman of the BSI commitee that drew up IEC60601-1. He was emphatic that provided internal clearances are OK no externally earthed testing point is required.

I was advised to open the case and look inside for a marked accessible earthing point to do tests to. If there wasn't one that WOULD be an issue.

I pointed out that:
(a) As best practice, tests must be completed upon closure of a case. Therefore closing the case after such a test would neccesitate a re-test.
(b) Given that we test thousands of items a year opening cases to perform such tests routinely would carry a small but in my opinion needless risk of human error with uncertain consequences.

His response was that our technicians should be sufficiently competent to remove half a dozen screws, attach an earth bonding lead to an internal test point, test the item, then close the case afterwards without incident.

Mr Mellish is undoubtedly very eminent but the practicalities of modern NHS work on the conveyor belt are that you ELIMINATE any risks you can. I eliminated that one by barring purchases of such items. That's my advice to anyone confronted by that situation.

Stuff like this will make a tremendous dent in the efficiency of departments and their ability to cover equipment adequately. Imagine the effect if 20% of your stock requires case opening to effect a simple and what would have been quick safety test!

As regards acceptance, since it can't pass to Class 1 and shouldn't be tested to Class 2 since that test is inadequate for the purpose FAIL IT.

Marc

Hi Marcel,

I disagree - it shouldn't be failed on grounds of safety since, adhering to the standards, it may meet and exceed the requirements of the standard if not the spirit of it (the intended purpose of the clause or sub-clause). To argue might be very difficult if not impossible.

What I do agree with you on is that as purchasers we are in a position choose whether a product meets our needs and if it doesn't to reject it. Clinical and technical evaluation prior to purchase is probably the best way forward.

Hi Marcel

Another point to what you are saying is that by opening the case, you can be negating the warrenty.

The only way that we can see round it, is to attach a extra lead to the mains input with an exposed earth. Therefore you can test as Class 1.

Billy

Some suggestion.
Option 1:
As part of the negotiation to purchase, ask the company to commission the new equipment on site and provide you with a test certificate. Then put it on a service contract with the company.

Option 2:
Reprogramme your automatic tester with a class1 test that has the earth continuity test removed. If you have a tester that you cannot set up custom tests on, get our some resistors and capacitors, a DMM and try to remember how to do it the old way. That will tax quite a few people brought up on automatic testers.

Before people say it is not a full test if you do not check the earth; do you test every exposed metal part individually when doing an earth continuity test or just attach the probe to the earth stud and hope all the other parts are connected to it?

Robert

Just to add to the mix so to speak.

506N3 tech specs

Bottom of page.

Anybody out there familiar with the GE Dinamap PRo series vital signs monitor? Class 1 BF, non-accessible earth, non-earthed accessible parts.
I test Class 1, non-accessible earth, and test the accessible conductive comms connector for enclosure leakage and insulation resistance (which are included in Class 1 EST). There's no accessible conductive parts, that are earthed, to test - I test the mains IEC earth-bond seperately.

Under normal and SF condition, with no accessible earthed conductive parts on the enclosure, adequately isolated non-earthed accessible conductive parts on the case, and with adequate mains to earth seperation internally, electrically and mechanically sound enclosure, what's the most significant risks to the patient or operator on this Class 1 piece of equipment?

Is it if the earth becomes O/C internally or the earth in the mains lead fails between inspections or is it if a live part detaches and comes into contact and causes excessive leakage current or voltage on the non-earthed accessible connector, for example?

By internal inspection on evaluation it can be determined that neither of the internal failures is likely to occur in normal use and a life-threatening, high-risk, scenario under SFC is unlikely (although there were problems with securing the IEC sockets, on earlier versions, hence difficulty in keeping exposed mains inside the device!).

The failure of the detachable mains lead due to flexing and abuse is much more likely nowadays. EST is about looking as much as testing with an instrument. EST still requires those doing the testing to know what the test instrument is doing and why.

I open up equipment routinely on service to do repairs and routine servicing so looking for simple connection problems is not really too much trouble. We inspected on evaluation at the last place I worked - before we decided to puchase - this meant we knew what the build quality was like and how to test the device before we bought it. The PPQ, supporting documentation and equipment markings give us the information necessary to apply the essential tests.

If it's class 1-whatever but it doesn't have an accessible earth, don't you test it to class 1-whatever but note it as not having an accessible earth?

Cheers
Mark

Mark, we use an in line 'box' which measures both earth continuity of the mains lead and leakage currents from the machine on test.
I guess that the weakness of our system is that we cannot really ensure that any connected earth return lead within the equipment on test is operating as intended.
As Richard suggests, an internal inspection and perhaps a megger tester could allay any concerns that you may have but from a practcal point of view perhaps the equipment could be considered as having class 2 protection anyway as there are no accessable parts which could become live to the user and there is a distinct air gap between live parts and an otherwise insulated case assembly.
A can of worms maybe, but we have to consider what risks are present in real terms.
Perhaps these sort of questions should really be directed towards the manufacturers and the regulatory bodies......?

A megger tester doesn't come into it - a Class 1 test (~500Vdc insulation test) is provided on safety testers, pre-programmed - L/N-E, non-earthed accessible parts, i.e. enclosure-earth, applied parts-earth (for BF/CF), for example. A device without an accessible earth can never be assumed to have Class 2 protection - it would be marked as Class 2 if it did.

I'll say it again (just in case it was missed the first and second time) - assume a device with non-accessible earthed parts is Class 2 when it's Class 1 and apply Class 2 EST rather than Class 1 EST using a standard pre-programmed safety tester (in auto or manual mode) then you're likely to miss important tests that establish safety of the device.

In particular if the Class 1 device has either non-earthed accessible, conductive, parts, applied BF/CF parts or both conductive accessible parts and floating applied parts. Safety testers will usually only apply relevant tests depending upon the class and the type of applied parts we tell it we're testing to.

We have to do the rest like choose the correct class, type, connect the DUT and probe test points appropriately, as and when necessary during the test sequence. If we don't then what's the point of testing - it's just wasted time otherwise - and not worth doing at all if it's considered as wasted time when done properly, in my opinion.

Why all this jumping through hoops? If electrical safety testing of medical equipment is required at acceptance and/or during routine maintenance, then guidance (why not regulations, I wonder?) from the appropriate bodies (MHRA or whomever) should be crystal clear. Such guidance needs to be reviewed from time to time in light of "advances" in technology and manufacturing methods, I might add. It should not be for mere mortals like us techs to be for ever wringing our hands over this stuff.

Hopefully there will be guidance and standards on routine testing in the near future; for those that want to be told where to connect the probe, which button to press, how long to press it for, and which indicator to look out for.

I think you already know where you should stick your probe, Richard!

I understand Criticare are retrospectively going to fit an earth stud to the outside casing. Funny that.

Most ClassI equipment has some ClassII parts on it - not every single part of a ClassI device is earthed. These instances are covered in the standards for testing.
In these cases we are dealing with a special case where the whole of the case is a ClassII part of a ClassI device.
If you are testing for electrical safety - not type testing!! - you need to test what you have. Test all the ClassII parts as ClassII parts, if they pass the device will be elctrically safe. Enclosure leakage test being done as per standard with a defined sized foil being applied with a defined pressure, as you do on all ClassII parts of a ClassI device don't you?
How many people use the earth connector to test for enclosure leakage and ignore all the plastic case where you could have inductive and capacitive leakage currents?
The safety of the device is not reliant on it having an earth if there are no accessible earthed or uninsulated conductive parts?
Its function might require an internal earth but we are discussing safety testing.
Robert

The manufacturer states the device is Class 1 CF.

Concerning medical equipment, with applied parts, I think it does. What about applied parts leakage w.r.t earth?, for example, (irrepsective of whether there are accessible earthed parts on the case or not).

How do we know that applied parts on a Class 1 device with "Class 2 parts" are isolated from earth (or with mains on applied parts w.r.t earth) if we test Class 1 devices with "Class 2" parts as Class 2 overall?

Even if we test Class 2 and assume a "functional earth" there's still a requirement to test functional earth leakage and touch currents, etc, plus applied parts w.r.t earth on Class 2 devices is there not?

If we don't test Class 1 then this implies that there's no earth bond test performed on the 3-pin removeable IEC leads fitted to devices with "Class 2 parts", i.e. inaccessible earths.

In my opinion it's better practice to test Class 1 devices (with inaccessible but protective earths) as Class 1, mark the earth as inaccessible, then test the mains IEC earth bond seperately, followed by the tests actually required for a Class 1 device, rather than miss earth-referenced leakage tests, etc, because Class 2 EST is performed.

We must trust manufacturers and notified bodies to classify their products and then test them appropriately - precisely because we're not type-testing. Mains electrical devices are either Class 1 or Class 2 - nothing in-between as far as I'm aware.

A colleague in my department manufactured in line insulated boxes with and accessable earth point (standard 4mm socket).
We have been looking at the benefits of using this device and from a positive point of view we can check the earth continuity of the mains lead and can also monitor earth leakage current. Since there is no exposed conductive path then there seems no further benefit unless the device has a patient connection.

Any thoughts?

ps Orders can be placed via private message....

Thanks for all your contributions.

JohnBhoy - RL Dolby, who sold the uniits to us, have informed us that Criticaire are fitting earth studs to units in future manafacture, but not to units already sold.

The agreement is that we open the unit (and therefore break the seal stating warranty void if broken) and test, as a few of you have suggested to an internal earth point.


Mick