supplementary bonding

[JohnW2]

Class II appliances must not have a protective earth terminal. Showers are usually Class I products as the heat exchanger is usually earthed.

I agree that if there are internal parts which need to be earthed, it would seem odd/unusual to call it Class I, although the BS7671 definition of Class I does not really seem to preclude there being earthed internal parts, provided they are surrounded by double/reinforced insulation.

If plastic parts are used in a Class I appliance to protect from access to live parts, this is known as Class II construction in a Class I appliance. Where there is Class II construction, the insulation must be double or reinforced.

I have to take your word for that, but I don’t quite understand the significance of “having Class II construction” when one is saying that an item is Class I. What is the significance of the difference between a Class I item which does have “Class II construction” and one that doesn’t?

There are many ways an insulation system in an appliance can be evaluated, three common senarios are:
Live part - 3.5mm air - plastic enclosure. Here the 3.5 mm of air provides the reinforced insulation and the enclosure is just an enclosure
Live part - 2mm air - 1mm min. thick plastic enclosure. Here the air provides basic insulation and the enclosure provides supplementary insulation giving double insulation
Live part touching 2mm min. thick plastic enclosure. Here the enclosure provides reinforced insulation

I find that hard to understand/believe. The vast majority of plastic-enclosed item would satisfy one of those conditions - but you’re not saying that they would therefore all qualify as Class II, are you?

What might one consider earthing in a Class II appliance? If it's a metal encased Class II appliance (there obviously are some) what harm could/would come from earthing that metal case?

The appliance would become a Class I appliance. You would have to perform various tests to ensure protective earthing system was adequate

I don’t really understand that, either in terms of electrical common sense or BS7671 definitions. The degree of protection against electric shock provided by a Class II appliance does not reduce if one puts it inside a metal enclosure, whether that enclosure is earthed or not. Since protection does not rely on the earthed enclosure, the adequacy of the earth is irrelevant. Furthermore, if the object within it is already Class II, I would not think that, at least in common sense terms, a metal container in which it is placed counts as an exposed-conductive-part of the item it encloses, does it?

Kind Regards, John

 

[EFLImpudence]

Not really sure. I just have in mind the 'tingles'. Are you saying it is not necessary to check?

Not necessarily -

If it's not necessarily necessary to check then when and how would you check it?

but there's no real point in 'checking' (the resistance between pipes) unless you know how to interpret the result in terms of whether or not SB is required! ... there's quite a big difference between, say, [50 x 230 / 30] (383&#937 and [50 * 230 /250] (46&#937.

I'm confused. Why have you multiplied by 230?

 

[EFLImpudence]

Class II appliances must not have a protective earth terminal. Showers are usually Class I products as the heat exchanger is usually earthed.

I agree that if there are internal parts which need to be earthed, it would seem odd/unusual to call it Class I, although the BS7671 definition of Class I does not really seem to preclude there being earthed internal parts, provided they are surrounded by double/reinforced insulation.

Have you made any typos?

Isn't that the precise definition of Class I; that they include protection by a CPC in the fixed wiring?
There being no provision for such in Class II.

 

[JohnW2]

Class II appliances must not have a protective earth terminal. Showers are usually Class I products as the heat exchanger is usually earthed.

I agree that if there are internal parts which need to be earthed, it would seem odd/unusual to call it Class I, although the BS7671 definition of Class I does not really seem to preclude there being earthed internal parts, provided they are surrounded by double/reinforced insulation.

Have you made any typos?

I don't think so - although it wouldn't be the first time

Isn't that the precise definition of Class I; that they include protection by a CPC in the fixed wiring?

Not really. The BS7671 definition is that basic protection against electric shock is supplemented by the earthing of exposed-c-ps. If there are no exposed-c-ps, there clearly aren't any to earth (and the presence of earthed components within the "Class II construction" does not alter that).
Edit: I should have added "...but Chris is telling us that (because it has earthed internal parts) a shower is Class I, even though it doesn't have any exposed-c-ps".

Kind Regards, John

 

[JohnW2]

Not really sure. I just have in mind the 'tingles'. Are you saying it is not necessary to check?

Not necessarily -

If it's not necessarily necessary to check then when and how would you check it?

You have to tell me that, since you're the one who introduced the idea of 'checking'! Don't forget that the regs do not explicitly talk about this checking (to see if SB is required) - you are 'adapting' the test they indicate for determining whether SB (which exists) is adequate.

but there's no real point in 'checking' (the resistance between pipes) unless you know how to interpret the result in terms of whether or not SB is required! ... there's quite a big difference between, say, [50 x 230 / 30] (383&#937 and [50 * 230 /250] (46&#937.

I'm confused. Why have you multiplied by 230?

Probably because it was late at night and I was probably half asleep! Goodness knows why I did that (particularly because of the totally stupid answers I got, and posted) - I must have been in some sort of 'autopilot' mode!! To properly rephrase my statement: "... there's quite a big difference between, say, [50/30] (1.67&#937 and [50/250] (0.2&#937"
Sorry about that!

Kind Regards, John

 

[EFLImpudence]

That's a relief.



Forget my checking, then, and accepting that you are correct in that, with no exposed-c-ps in the room, no SB is required, why do you not accept my proposal that the rider of "according to 415.2" means that the rest of 701.415.2 only applies to items which have exposed-c-ps and, indeed, are simultaneously accessible?

This makes sense and would then agree with your interpretation.

 

[JohnW2]

That's a relief.

Apologies again. I've been trying to work out how my 'autopilot' managed to do that. I can but presume that, because the 415.2.2 equations (well, strictly, 'inequalities') include "50 V", some corner of my half-asleep mind interpreted the "V" as Uo! However, even that doesn't excuse me for not having noticed that the answers I got (and posted) were stupid!

Forget my checking, then, and accepting that you are correct in that, with no exposed-c-ps in the room, no SB is required, ....

I don't think I've ever said that, certainly not in terms of what the regs 'require'. What I have said is that I can see no 'electrical sense' in connecting any SB to the CPCs if there are no exposed-c-ps - but the regs (both 415.2 and 701.415.2) do appear to require that.

... why do you not accept my proposal that the rider of "according to 415.2" means that the rest of 701.415.2 only applies to items which have exposed-c-ps and, indeed, are simultaneously accessible? This makes sense and would then agree with your interpretation.

We've been through this, and it all depends upon how one interprets 415.2. If one interprets it as saying that SB necessarily requires that at least one extraneous-c-p and at least one exposed-c-p be 'simultaneously accessible (touchable)' (i.e. taht there must be at least one of each), then one obviously cannot have SB unless both extraneous- and exposed-cps are present (and 'simultaneously accessible'). However, another interpretation (which would work in your 'anti-tingle' scenario) is that one can have SB if there are 'simultaneously accessible' extraneous-c-ps (but no exposed-c-ps), or 'simultaneously accessible' exposed-c-ps (but no extraneous-c-ps).

If your interpretation is that one can't have SB (as defined in regs) in the absence of exposed-c-ps, then are you going to say that your ('anti-tingle') joining together of extraneous-c-ps (without connecting them to anything else) is something other than 'SB'? - i.e. are we just talking about semantics/terminology?

Kind Regards, John

 

[Chris61]

Here are the definitions from EN 60335-1

3.3.9 class I appliance

appliance in which protection against electric shock does not rely on basic insulation only but which includes an additional safety precaution, in that conductive accessible parts are connected to the protective earthing conductor in the fixed wiring of the installation in such a way that conductive accessible parts cannot become live in the event of a failure of the basic insulation

NOTE This provision includes a protective earthing conductor in the supply cord.

3.3.10 class II appliance

appliance in which protection against electric shock does not rely on basic insulation only but in which additional safety precautions are provided, such as double insulation or reinforced insulation, there being no provision for protective earthing or reliance upon installation conditions

I know the definition of Class I states that conductive accessible parts are connected to the PEC and most showers do not have accessible metal parts but the standard specifically states that Class II appliances must not have an earthing terminal.

 

[EFLImpudence]

Forget my checking, then, and accepting that you are correct in that, with no exposed-c-ps in the room, no SB is required, ....

I don't think I've ever said that, certainly not in terms of what the regs 'require'. What I have said is that I can see no 'electrical sense' in connecting any SB to the CPCs if there are no exposed-c-ps - but the regs (both 415.2 and 701.415.2) do appear to require that.

But I don't think 415.2 does say that.
It says that SB shall include ALL simultaneously accessible exposed-c-ps AND extraneous-c-ps.
Therefore this does not include parts which are NOT any of these.

If your interpretation is that one can't have SB (as defined in regs) in the absence of exposed-c-ps, then are you going to say that your ('anti-tingle') joining together of extraneous-c-ps (without connecting them to anything else) is something other than 'SB'? - i.e. are we just talking about semantics/terminology?

No.
Your definition of SB seems to be specific to that described to equalise potential in a bathroom.

'Supplementary' just means 'additional' or 'extra' or 'more' such that ANY bonding ANYwhere which is used in addition to main bonding is 'supplementary' bonding.
Plumbers' 'cross-bonding' (albeit unnecessary) is 'supplementary' bonding.

 

[JohnW2]

Here are the definitions from EN 60335-1
3.3.9 class I appliance
appliance in which protection against electric shock does not rely on basic insulation only but which includes an additional safety precaution, in that conductive accessible parts are connected to the protective earthing conductor in the fixed wiring of the installation in such a way that conductive accessible parts cannot become live in the event of a failure of the basic insulation

3.3.10 class II appliance
appliance in which protection against electric shock does not rely on basic insulation only but in which additional safety precautions are provided, such as double insulation or reinforced insulation, there being no provision for protective earthing or reliance upon installation conditions

I know the definition of Class I states that conductive accessible parts are connected to the PEC and most showers do not have accessible metal parts but the standard specifically states that Class II appliances must not have an earthing terminal.

Thanks. Those definitions are essentially the same as the BS7671 ones, particularly in that the definition of Class I refers to 'conductive accessible parts' (which BS7671 calls 'exposed-conductive-parts'). As we have both said, showers do not usually have any such exposed/ accessible conductive parts which one can earth to provide additional protection.

Your argument is really relying on the fact that the definitions of Class II say that there is "no provision for protective earthing" or "no earth terminal", but does that not simply mean that is there is (maybe 'must not be') any provision for earthing any accessible/exposed conductive parts (if there are any) - rather that one literally is not allowed an 'earth terminal', or even parts which are earthed within the double/reinforced insulation? Class II items often do have 'earth terminals', kindly supplied by the manufacturer as somewhere to safely terminate the supply cable's CPC (which BS7671 requires to be present, even if it's Class II). As I've said before, although it may be the case, it makes no electrical sense to me that one is not allowed to have earthed parts within a Class II item.

Class I/II is surely all about the means of adequately protecting people (over and above the protection provided by 'basic insulation') from electric shocks, isn't it? What I don't really get is that there almost seems to be a classification 'missing'. If the only accessible parts of an item are plastic, then there is clearly no way that the additional protection against electric shock (additional to 'basic protection') can be provided by earthing exposed/accessible-conductive-parts, since there aren't any - so surely can't satisfy the definition of Class I? (which is why I don't understand how a shower can be called Class I)! Does that mean that if an item is entirely plastic-enclosed, then it must be constructed (double/reinforced insulation) so as to meet the requirements of Class II - given that (except for SELV), one only has Classes I and II to choose between?

Kind Regards, John

 

[JohnW2]

I don't think I've ever said that, certainly not in terms of what the regs 'require'. What I have said is that I can see no 'electrical sense' in connecting any SB to the CPCs if there are no exposed-c-ps - but the regs (both 415.2 and 701.415.2) do appear to require that.

But I don't think 415.2 does say that. ... It says that SB shall include ALL simultaneously accessible exposed-c-ps AND extraneous-c-ps. Therefore this does not include parts which are NOT any of these.

When talking about 415.2.1 you always appear to be focussing on the statements about (extraneous- and exposed-) 'conductive parts', but ignoring the final sentence about CPCs, which reads "The equipotential bonding system shall be connected to the protective conductors of all equipment including those of socket outlets". So, as I read it, if there is any SB, it has to be connected to the CPCs.

If your interpretation is that one can't have SB (as defined in regs) in the absence of exposed-c-ps, then are you going to say that your ('anti-tingle') joining together of extraneous-c-ps (without connecting them to anything else) is something other than 'SB'? - i.e. are we just talking about semantics/terminology?

No. Your definition of SB seems to be specific to that described to equalise potential in a bathroom. 'Supplementary' just means 'additional' or 'extra' or 'more' such that ANY bonding ANYwhere which is used in addition to main bonding is 'supplementary' bonding. Plumbers' 'cross-bonding' (albeit unnecessary) is 'supplementary' bonding.

Despite your 'No', it's looking increasingly to me as if we probably are primarily talking about terminology. As you say, 'bonding' (or even 'equipotential bonding') refers simply to the connecting together of any two or more things to minimise pds between them - and those things could be a spoon and a doorknob if one felt there was some need to do it. Furthermore, as you say, anything which is not 'main bonding' is 'supplementary bonding'.

Hence, in terms of the English, any connecting together of any two or more things with the view to minimising pds could be described as 'supplementary bonding'. However, is seems to me that BS7671 has gone beyond the English, and has created a more specific concept of 'Supplementary Bonding' which requires the joined-together items also to be connected to CPCs. That wouldn't be unusual - if you look at Part 2 of BS7671, you will find plenty of words/phrases which have been defined, for the purpose of BS7671, to have a more specific meaning than the same words/phrases have in 'everyday use'.

Kind Regards, John

 

[EFLImpudence]

Good point; I have been overlooking the reference to socket outlets.

In that case, even if there were NO exposed-c-ps (or even NO parts - maybe just a plastic light out of reach) in the bathroom, do you think that the extraneous parts would still require bonding for persons using hand held appliances (vacuum?) even though they would, presumably, not be wet or even involving water - and, if so...

would this necessitate connection to the CPC of the inaccessible light?

 

[JohnW2]

Good point; I have been overlooking the reference to socket outlets. ... In that case, even if there were NO exposed-c-ps (or even NO parts - maybe just a plastic light out of reach) in the bathroom, do you think that the extraneous parts would still require bonding for persons using hand held appliances (vacuum?) even though they would, presumably, not be wet or even involving water - and, if so... would this necessitate connection to the CPC of the inaccessible light?

You tell me - as I said, these aspects of the regs seem to me to have mud-like clarity! However, I think that it is certainly possible to read/interpret the regs such that the answers to both your questions would be 'yes'!

I must admit that, if I were ever faced with such a situation, I would probably 'resort' to common sense, whatever the regs might be trying to say!

Kind Regards, John

 

[Chris61]

Thanks. Those definitions are essentially the same as the BS7671 ones, particularly in that the definition of Class I refers to 'conductive accessible parts' (which BS7671 calls 'exposed-conductive-parts'). As we have both said, showers do not usually have any such exposed/ accessible conductive parts which one can earth to provide additional protection.

Your argument is really relying on the fact that the definitions of Class II say that there is "no provision for protective earthing" or "no earth terminal", but does that not simply mean that is there is (maybe 'must not be') any provision for earthing any accessible/exposed conductive parts (if there are any) - rather that one literally is not allowed an 'earth terminal', or even parts which are earthed within the double/reinforced insulation? Class II items often do have 'earth terminals', kindly supplied by the manufacturer as somewhere to safely terminate the supply cable's CPC (which BS7671 requires to be present, even if it's Class II). As I've said before, although it may be the case, it makes no electrical sense to me that one is not allowed to have earthed parts within a Class II item.

Class I/II is surely all about the means of adequately protecting people (over and above the protection provided by 'basic insulation') from electric shocks, isn't it? What I don't really get is that there almost seems to be a classification 'missing'. If the only accessible parts of an item are plastic, then there is clearly no way that the additional protection against electric shock (additional to 'basic protection') can be provided by earthing exposed/accessible-conductive-parts, since there aren't any - so surely can't satisfy the definition of Class I? (which is why I don't understand how a shower can be called Class I)! Does that mean that if an item is entirely plastic-enclosed, then it must be constructed (double/reinforced insulation) so as to meet the requirements of Class II - given that (except for SELV), one only has Classes I and II to choose between?

Kind Regards, John

I don't know the exact reasoning behind requirements of the standard with regard to Class I/II and earthing, I wish I did.

I do know that the standard specifically states that Class II appliances shall have no provision for earthing (Clause 27.1). I have seen Class II appliances with terminals for "parking" a CPC and this is considered okay as long as the conductor is not connected to anything. I assume the prohibition of an earth connection is something to do with avoiding importing an unwanted potential?

There is a requirement for Class II appliances connected to the water mains to have double or reinforced insulation between metal parts in contact with water and live parts. I presume it is easier to make the heat exchangers with basic insulation and to earth them which is why showers are Class I. It's often easy to overlook the accessible parts of an appliance and of course the connection to the water mains is one. It must be assumed that the shower is going to be plumbed using metal pipes.

In 60335, an appliance using only SELV is known as Class III, This again must have no earth as SELV circuits must remain safe during an earth fault.

 

[JohnW2]

I don't know the exact reasoning behind requirements of the standard with regard to Class I/II and earthing, I wish I did.

From what I can see, and what you're saying, it certainly does not seem to make a lot of electrical common sense!

I do know that the standard specifically states that Class II appliances shall have no provision for earthing (Clause 27.1). I have seen Class II appliances with terminals for "parking" a CPC and this is considered okay as long as the conductor is not connected to anything.

As I said, I suspected that (even though I don't understand why it's needed) the prohibition of "provision for earthing" was probably intended to mean "provision of earthing of any exposed/accessible-c-ps".

I assume the prohibition of an earth connection is something to do with avoiding importing an unwanted potential?

I don't think I would assume that, because it appears to make no sense. Earthing of any conductive parts, even if not exposed/accessible ones, would, if anything, increase safety, and earth will not be at a significantly different potential from the neutral which is inevitably already going to be present.

There is a requirement for Class II appliances connected to the water mains to have double or reinforced insulation between metal parts in contact with water and live parts. I presume it is easier to make the heat exchangers with basic insulation and to earth them which is why showers are Class I.

Maybe - but, as you know, I don't really understand why having (inaccessible) earthed parts within an item necessarily stops it being Class II, if there is double or reinforced insulation between the innards and the outside world!

It's often easy to overlook the accessible parts of an appliance and of course the connection to the water mains is one. It must be assumed that the shower is going to be plumbed using metal pipes.

At least for many recent years, I don't think I've seen a shower which had metal pipe unions. The plumbing system may be metal, but the parts of the shower they connect to are invariably plastic.

In 60335, an appliance using only SELV is known as Class III,

Indeed - that's why I said that "(except for SELV)" one seemed to only have a choice between Class I and Class II (Class 0 being effectively prohibited).

IThis again must have no earth as SELV circuits must remain safe during an earth fault.

Well, yes, that's what the "S" of SELV means - but that's a different matter.

Kind Regards, John