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Posted By Topic: Class 1 or Class 2 query

YeahNah
Apr 08 2016 20:31

I have a device that on the manufacturing plate clearly says it is a Class 1 (earthed) device.

It is powered by a standard 3 pin IEC lead and the socket on the device has an earth pin.

However there is no externally available earth connections, none at all, zero, zip, nada, nothing.

I contacted the overseas supplier who says to do a Class 1 test you have to unscrew and remove the cover and then attach your earth test probe to the internal metal frame that is connected to the earth pin of the appliance socket.

A bit like taking the cover off and attaching the earth probe to the body of an internal transformer.

As far as I know this is not a class 1 device.? or at the very least not as we know it...
   

TheDon
Apr 08 2016 21:39

I think your looking at it the wrong way , If it is not class 2 and it sounds like the manufacturer does not think so , then it must be class 1. just because it doesn't have any exposed metal doesn't make it class 2
   

YeahNah
Apr 09 2016 08:30

Yes you are correct, but what I forgot to say is what would be the annual EST requirements (it is a medical device) must I remove the cover and test the earth integrity, I'm 99.5% sure I don't but am just looking for confirmation.
   

pluto
Apr 09 2016 11:38

If the manufacturer claims that the appliance is "double insulated" it is requirement of all standards in normal everyday use for the words
"double insulated"would be on the name plate giving the voltage, amps.wattage and frequency.

An alternative marking is the international symbol of a "square within a square".

If it does NOT have these markings it is NOT a "class II" appliance. See as/nzs 3000 clause 1.4.28 for a description of what double insulation or Class II means in the construction of appliances.
   

Kingswell
Apr 09 2016 20:43

See AS/NZS 3760:2010 Appendix A, note (2): “Some hybrid constructions exist whereby Class I equipment is totally encapsulated”. This your appliance may fall within this description, but I don’t know whether you can use these notes for medical equipment. One of our experts will know.
   

YeahNah
Apr 09 2016 23:07

This is the label on the name plate.
   

YeahNah
Apr 09 2016 23:10

So my question is, given it states it is a Class 1 device, but there are no external earth points, how can it be tested as a Class 1 device, other than to test the lead.

I'm sure I have read somewhere that if it is a Class 1 device but there are no external earth points, then you do not need to disassemble the device to find one for the purposes of the annual EST.
   

AlecK
Apr 10 2016 07:29

ESR 90 points us to AS/NZS 3551 for testing electrical medical equipment
   

Kingswell
Apr 10 2016 08:10

Re comment “I have read somewhere that if it is a Class 1 device but there are no external earth points, then you do not need to disassemble the device to find one”.

You may be thinking of AS/NZS3760:2010 2.3.3.9, which basically says this – when read in conjunction with 1.1.3.
BUT your appliance is a medical electrical device, Type BF, so it has to be tested under AS/NZS3551:2012; as it has a detachable power supply cord, it appears to me that the testing of the protective earth has to be done as per B8.3. Then, you have to do the Earth Leakage Current Test as per B11, then do the Patient Leakage Current Test as per B12.2.

If the applied parts are double insulated, how do you test them? I haven’t been able to find anything in 3551 that specifically applies. Best suggestion I’ve found is wrapping the double insulated part in aluminium foil as per AS/NZS 3760 Appendix A, A2 note (1). But 3760 doesn’t apply to Medical equipment.

   

ShaneR
Apr 10 2016 09:13

"Yes you are correct, but what I forgot to say is what would be the annual EST requirements (it is a medical device) must I remove the cover and test the earth integrity"


So you test and tagging?


I assume you would need to change the tag to say tested to AS/NZS3551


Also AS/NZS3760:2010 A2 Note 2

You don't need to test?
   

wireman
Apr 10 2016 11:52

Slightly off current topic..

I want to test a Class II appliance for earth leakage (that I don't want to do an insulation resistance test on). I don't have a tester capable of testing differential leakage.

Can I connect a clip on to any exposed metal, and on to the installation earthing system, and measure the conductor with a meter capable of measuring mA with the required accuracy?

Now assume there is no exposed metal, would the only way to test this be with a device capable of differential testing?
   

pluto
Apr 10 2016 11:55

Being a medical device as/nzs 3551 is the applicable standard covering testing and a quick look of 3551 shows that all answers required for this post are contained in this standard

Note as/nzs 3760 will not apply for medical equipment.
   

Kingswell
Apr 10 2016 15:55

10 Apr. 16
Re YeahNah initial post Apr 08 2016 20:31
“I contacted the overseas supplier who says to do a Class 1 test you have to unscrew and remove the cover and then attach your earth test probe to the internal metal frame that is connected to the earth pin of the appliance socket.”
See AS/NZS3551 B8.1: ‘Reference shall be made to the manufacturer should there be no apparent exposed metal on a Class I device…”.

Re ShaneR comments Apr 10 2016 09:13
“I assume you would need to change the tag to say tested to AS/NZS3551”
Yes, the tag must refer to 3551, but there’s more than that. See 3551 2.4 Documentation Requirements, 2.5 Equipment Database, & 6.7 Review and Recording of Results.

“Also AS/NZS3760:2010 A2 Note 2. You don't need to test?”
You still have to test, just that one particular test can be omitted. BUT that is in 3760, not 3551.

   

ShaneR
Apr 10 2016 16:03

"You still have to test, just that one particular test can be omitted. BUT that is in 3760, not 3551."

Yes, sorry that is what I meant, and only for appliances covered under 3760
   

YeahNah
Apr 10 2016 18:03

I'm aware of the 3551 comment " ‘Reference shall be made to the manufacturer should there be no apparent exposed metal on a Class I device…”

The supplier has sent a pdf written in Ching-Lish saying " if you wanna to test the earth then take cover off and to test."

So it is not mandated manufacturers requirement to test the earth, just 'if you wanna to'

So I'm trying to work out if a medical device is Class 1 but it has no accessible external earth points.... must you take the cover off to test the earth.

Is there a linear yes/no answer.?
   

Kingswell
Apr 10 2016 19:02

I once has to ask an Italian manufacturer how to ascertain compliance on a light and metal arm combination mounted via metal bearings onto a dental chair. The light was plainly labelled as double insulated, but the bearings gave some contact through to the main frame of the chair. There was nowhere to attach a bond to the arm short of drilling a hole and bolting a lug onto it. I reckoned that the metal arm had to be either earthed OR insulated, not some random resistance depending on the position of the arm. The Italian company simply said that the light was double insulated and didn’t need earthing. I pointed out that I was asking about the arm, not the light. They finally gave some advice about an insulating bush that wasn’t there, but the response left the impression that no one else had asked about this before.
   

Kingswell
Apr 10 2016 20:20

Pluto, where can we find the solution to my above problem: If the applied parts are double insulated/plastic sheathed, how do you test them? I haven’t been able to find anything in 3551 that specifically applies. Best suggestion I’ve found is wrapping the double insulated part in aluminium foil as per AS/NZS 3760 Appendix A, A2 note (1). But 3760 doesn’t apply to Medical equipment.
I believe we should still do leakage tests on these items, in case any cracks or degradation through abrasion or impact has weakened the insulation.

   

pluto
Apr 10 2016 20:58

My copy of as/nzs 3551:2012 in appendix B11 covers how to do the earth leakage current testing and also specifies the maximum values permitted.
   

Kingswell
Apr 10 2016 21:36

Pluto, I’ve read both B11 & B12. It appears to me that everything they say applies to items which have a metal patient connection. Where do we find advice for testing double insulated/plastic sheathed applied parts – such as suction tube mouth pieces for dentists’ patients?
   

pluto
Apr 10 2016 22:29

My reading of clause B11.1 would indicate that the single item under test you use the supply lead cores to do the earth leakage testing with all external parts and connections disconnected.

If the item under test is part of a system of multiple items of mains powered equipment, there are other tests to take care that the collective sum of earth leakage currents is not excessive.
   

Kingswell
Apr 11 2016 06:42

Thanks Pluto. With due respect, in reading B11.1 in the 2012 edition of AS/NZS 3551, it says “removing all intended and unintended EARTHING CONNECTIONS…”. My question is about applied parts. OK, you do have to read a little further to B12.2 ‘Patient leakage current test’ to see the detailed illustrations about this; these illustrations all show the item under test sitting on an insulating base, which is obviously there to visually display isolation from unintended earthing connections (or ‘alternative earth paths’). Figures B8 & B9 show method of testing of applied parts, with the meter testing to ‘patient connections’, as per note B12.3.3 (a). I’m specifically looking for help on testing double insulated/plastic sheathed applied parts.
   

AlecK
Apr 11 2016 08:44

OK, so now we have 2 separate issues.
for the first one
The way I read it the EC test for class 1 equipment is mandatory.
There is no direct equivalent to the "3760" exemption for cases where there is no access to conductive parts.

However the Preface (as referred to in the Notes to the tests) says the testing is limited to "non-destructive". And as YeahNah has found, it suggests seeking advice from the manufacturer.

In this case their advice is fairly clear (at least as translated): if you wanna test the earth, then take the cover off"

Well we DO wanna test, because the Standard says we must (as long as the test isn't destructive).
So the answer is: take the cover off.

The suggestion to seek manufacturer;s advice isn't about WHETHER to do the test, it's about HOW to do the test.

That said, perhaps the question should be passed to the relevant Standards committee so they can consider whether an amendment is warranted. May be an exception similar to "3760". Or maybe just a clarification that the test is always to be done.
I suggest writing to SNZ in the first instance

-------------------

Second issue of testing DI bits mounted on earthed (or possibly earthed) object.

DI isn't about whether the external parts are fortuitously earthed or not.Its simply about the level of insulation between live pats and accessible conductive parts. Think chuck of drill, and any number of similar cases.
Being in a medical scenario makes no difference to this basic fact.

So if the light is clearly marked as DI, then treat it as DI. The metal arm is just that, a metal arm. It isn't part of the light.

Another example: a normal equipoise type table lamp. If you get a "Superlux" one, they use a brass lampholder that needs to be earthed (an is). Some other brands us a plastic lampholder that doesn't need to be earthed.
But in neither case is there any need to earth the equipoise arm, because the flex along it is DI for the entire length.

Back to the dental chair.
If its frame is earthed, the the arm will be earthed (whether it needs to be or not). That doesn't affect the fact that the light is a DI light.

(TIC: Unless of course the DI label was stuck on in the Auckland lighting warehouse of a well-known NZ lighting retailer.)




   

YeahNah
Apr 11 2016 14:03

Thanks AlecK

This device is a home based CPAP (sleep aponea device) that is being sold to a patient.

So it is not being used in a medical environment, let alone a hospital/clinic BF or CF area.

And I believe privately owned devices do not need regular testing.

So is it acceptable that as part of the sale, the device is dismantled and tested, then reassembled, sold and never tested again.
   

YeahNah
Apr 11 2016 14:29

This then raises the situation that if you dismantle a device to do the earth test, then reassemble the device, the Standard requires that after reassembly the device is electrical safety tested...

But how do you re-test the device after you have assembled it.?

I know...I know..!

Take the cover off...

Reassemble it...

But...
   

Kingswell
Apr 12 2016 22:16

AlecK, in response to your comments Apr 11 2016 08:44 about the DI light arm:
“DI isn't about whether the external parts are fortuitously earthed or not”
With respect, I thought that being in a medical scenario DOES make a difference. AS/NZS3551 B8 Protective Earthing Test says ‘Protective earthing shall be checked to verify a resistance of not more than 200mΩ between …. The earth terminal … and parts that are protectively earthed”. I had mentioned earlier that the arm was neither DI nor properly earthed, just occasionally earthed through random resistance depending on the position of the arm. Are you thinking that because this arm hasn’t actually been protectively earthed, it can be ignored? Or, are you relying on the curious comment in B8.5 (a)(iii), which could possibly be read to suggest that the absence of a protective earth conductor that flexes, means that this test can be omitted? But if either of these interpretations is allowed, how do you reconcile that with 7.3.2 paragraph 3 “…where more than one medical device is interconnected by … electrically conducting mountings … the testing of protective earth resistance between exposed metal … and the earth … etc”.?

   

AlecK
Apr 13 2016 10:56


" ‘Protective earthing shall be checked to verify a resistance of not more than 200mΩ between …. The earth terminal … and parts that are protectively earthed'.
I had mentioned earlier that the arm was neither DI nor properly earthed, just occasionally earthed through random resistance depending on the position of the arm. Are you thinking that because this arm hasn’t actually been protectively earthed, it can be ignored? "

Yes. The arm is a conductive part, but it's separated from live p[arts by DI.
exactly the same as the chuck on a drill.
If it gets fortuitously earthed by being in contact with something that's earthed - eg the chair it's mounted onto - absolutely no harm can arise.
And if it doesn't get fortuitously earthed, the same.


"Or, are you relying on the curious comment in B8.5 (a)(iii), which could possibly be read to suggest that the absence of a protective earth conductor that flexes, means that this test can be omitted? "

No


"But if either of these interpretations is allowed, how do you reconcile that with 7.3.2 paragraph 3 '…where more than one medical device is interconnected by … electrically conducting mountings … the testing of protective earth resistance between exposed metal … and the earth … etc'.?"

The lamp is not a medical device.
Not everything that's in patient treatment area is an "electrical medical device" (see the definition).
This particular rule is about the possibility of touch voltage due to high resistance earth paths between their conductive parts. Especially if both are earthed (Class 1) appliances, when a fault on one will have multiple fault current paths (and will take all of em to some degree).

The appropriate test for this arm is not earth continuity back though the luminaire supply, but insulation resistance (or leakage test) between it and the lumnaire's live parts.

If you want to test the arm's earth continuity back through the chair, feel free; but it won't prove anything.

The whole point of DI is to avoid having to earth extraneous conductive parts. It' a completely different method of fault protection from "automatic disconnection" (see "3000" clause 1.5.5).
And being in a medical situation may up the ante, and may alter the permited parameters for the chosen method (to keep touch voltages and so current applied to victims lower) but it doesn't change the basics.
Aotomatic disconnection requires an earthing system.
Isolation requires an equipotential bonding system.
DI requires neither.

   

Kingswell
Apr 15 2016 22:06

Thanks Alec, very helpful and detailed response. I agree that the lamp (in isolation) is not a medical device and I thank you for the thorough explanation of different methods of fault protection; but when the lamp (and various other electrically-powered items) are mounted on or attached to a dental chair, I reckon that it should be looked at as a ‘Medical Electrical System’. AS/NZS 3551 section 7 paragraph 2 says “A medical Electrical System is created when two or more devices, at least one of which is medical equipment, are interconnected electrically or functionally…”. If this is the case, we must apply 7.3.2 paragraph 3.
   

AlecK
Apr 18 2016 10:48

Several possible scenarios - and from here I can't tell which applies.

if the chair is also not medical electrical equipment, ie if it's just a chair that doesn't have internal contact with the patient, then the combination of chair + luminaire can't set up a "medical electrical system" (unless both are connected to some third item which is).
Just as a bed with electrics to operate tilting mechanism isn't medical electrical equipment, a dental chair isn't automatically medical electrical equipment.
But if it has medical electrical equipment that is integral to it, then it would be.



Now let's assume the chair is medical electrical equipment. There are 2 types of "medical electrical system" that can exist.

So is this a case of "multiple socket outlets" as per 7.2.1?
I doubt the chair is a plug-in device, so probably not. but assume it is a plug-in chair, the wording isn't about several items plugged into different sockets, it's about two (or more) items supplied from "a multiple socket outlet".
Is there such a fitting even in the room? Unlikely; given the restrictions in 7.2.1.

The way I read it, this is about having more than one item of equipment supplied from the same isolating transformer, and dealing with the possible fault scenarios that might arise from that. I'm betting that you don't have ANY "multiple socket outlets", and that all your sockets are supplied from an earthed supply via RCDs.

Is it a case of "functionally interconnected equipment" as per 7.2.2 ? doesn't sound like it. Functional interconnection is for things that are networked together. It deals with the (generally small) currents that can flow when two earthed items have their earthed parts connected together, eg when using comms cables that use earth as a conductor as well as, or instead of, as a screen.
Maybe there's a video camera that gets switched on when the chair is tilted back? 7.2.2 seems to cover it pretty thoroughly; and clearly it's not about simple fortuitous connection of earthed parts such as mounting this lamp to the chair.


So even if the chair is "medical electrical equipment", it still doesn't automatically create a "medical electrical system".



So now let's assume that not only is the chair medical equipment, but that some other item makes a "medical electrical system".
Could be something else bolted to the chair and fed from "a multiple socket" that also supplies the lamp (or the chair); or something functionally interconnected with the chair (difficult to imagine anything being "functionally interconnected" with the lamp, but I suppose it's possible).


Yes, IF a "medical electrical system" is created, then 7.3.2 will apply and some extra testing has to be done.

But that does NOT mean the arm supporting the DI lamp has to be earthed by the lamp's supply. It just means that those limits in para 1 of 7.2.3 have to be complied with.

Which won't be difficult, since there's no fault current path from the DI lamp, nor from anything else, to the arm; so there's no way it can be carrying current from any source. The only ways it can have its touch potential raised is by the chair becoming live or the DI breaking down.
Either way if the mounting is electrically sound the arm can't be at a different potential from the rest of the chair during a chair fault, so all we need to do is cover the case of the DI breaking down and livening the chair via the arm. We don't want any high-impedance in that fault current path.

So the appropriate test in this case is from the luminaire support arm to the earth of CHAIR's supply.
Think of the support arm as being part of the chair, rather than as part of the luminaire, or as something separate.
I know that sounds a bit illogical, but it's not about whether it all arrived in one box or two, but what's happening electrically. What matters is that electrically the arm IS part of the chair, and what we're trying to avoid is differences in potential between different parts of the chair (regardless of the source of the potential). As long as the arm is effective tied to the chair's earth, and there's a good IR test between the lamp and the arm, there's no problem.
And of there isn't actually a "medical electrical system", don't even need to test the earth continuity from luminaire arm to chair earth; just the IR test between arm & lamp.

-------

BTW, thanks for asking this; I hadn't even realised that my "3551" was out of date, until you referred to a clause 7 that I didn't have. This is not an area I get involved in much.
Always good to learn new stuff.

But as always, when looking at new stuff leave your preconceptions behind. Read slowly. Read carefully. Read several times. And take particular note of any unusual wordings.

In this case the difference between "multiple socket outlets" (or "different socket outlets"); and the actual words used "a multiple socket outlet" (singular) is an indication that we're dealing with something a bit different. Then the restrictions on having them tell us what that difference is, and an understanding of isolated systems then explains why it could be a problem.




   

JeddaTuuta
Sep 20 2016 10:26

Not sure how large the equipment is that you are trying to test but have you thought of using tin foil or mesh? I wouldnt suggest you opening up hospital equipment unless you are trained to do so.
   

benben
Sep 20 2016 18:38

what is the screw holding the cover on screwed into?
   

hamburger
Sep 20 2016 21:50

AS/NZS3551 was updated just this month in fact 11 days ago. there is a new section covering loan/lease and hireage of electro medical devices among a few other additions.
its an interesting conversation this one and I have only just perused it however as I work predominantly in the electro medical field my advise is unless you can competently test any medical devise with the appropriate calibrated test gear, stay well away from putting your details on the tag (note the changes in amendment 2 of 3551 to what is required on the test tag). As your devise is a BF rated bit of kit, I'd be employing the services of a qualified biomed to test on your behalf. Emed is a specialist HR field like hazardous areas, or mines if you want, so competency is a prerequisite.