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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.