supplementary bonding

[JohnW2]

Just to clear up the shower Class I/II thing... Showers are usually Class I with Class II construction. There has to be double or reinforced insulation between live parts and the accessible plastic cover. This is usually provided by the cover itself, the air between the cover and the live parts or a combination of the two.

That's interesting, but I'm not sure that I understand! If they are have "Class II construction", with double or reinforced insulation, why are they not Class II?

Kind Regards, John

 

[EFLImpudence]

and I'm lead to believe even with plastic supply as above the water pipes need bonding too.
No, as long as none of the copper pipes reenters the ground.

I was told even though the water pipes will not provide a route to earth due to the plastic entry, if due to fault the water pipes became live, and for instance I touch the tap and metal shaver socket then I create a link between the shavers earth and the live water pipes.. is that in any way possible or am I being fed a load of rubbish? ( if it is and i don't need any sup.bonding please answer the rest of my questions anyway for educational purposes if nothing)

That is not the purpose of bonding.
You do not have to consider the pipes becoming live.
It is to equalise potential between the pipes if they would introduce true earth (ground) potential which may be different than the electrical installation earth

assuming the above is incorrect and supp. bonding of water pipes is not needed

No. That was MAIN bonding. you may still require supplementary bonding in the bathroom to equalise potential between parts there.

then am I right in thinking I should remove the water pipes main bond I installed as this is providing the pipes with a route to earth eliminating the protection of the plastic supply pipe?

It won't do any harm as the pipe will be connected to the installation earth by the boiler, immersion etc. but it can't introduce ground potential so there is nothing to equalise.

what i meant here was can I take the bond to just one of the pipes feeding rad. or does it need to be both pipes?

Probably.

Finally I'm planning to use 4mm2 does the supplementary bond have to be unbroken.

by this I meant does the sup. bond need to be one continuous wire or can it be a small peice just from hot to cold pipe and the a separate peice of wire connecting shavers CPC to cold water pipe... and so on?

Yes, just pieces where needed.

so.. though the CPCs of both circuits (light & shaver unit) are in effect acting as a bond via the CU,but to reduce resistance in the event of a fault I should take a sup. bond wire from shaver units CPC to the light rose CPC then to the nearest water pipe.

Yes.
However, if you have read all the post, we are discussing if this is really necessary where there are actually no exposed-conductive-parts.

then with a separate piece of bond wire I can connect the basin H&C (which in effect connects the showers H&C) to one of the radiator pipes, and this would complete the sup. bond?

Yes.

 

[EFLImpudence]

Because it (415.2) states extraneous and exposed-c-ps.

You've rather lost me. When do you think that the requirement of 710.415.2 that SB has to be connected to CPCs does apply, then?

When there are exposed-c-ps present.

The same as when it is stated in 411.3.1.2 that extraneous-c-ps must be main bonded.
Then somewhere else, 544.1.2 it states that e MEB connection to any water service shall be made... without stating that this only applies if the pipe is extraneous.

Is this somehow related to the GN8 Figure you referred to in which CPCs (I presume) were all joined together, despite the absence of either extraneous or exposed cps?

No. I am discounting that.

 

[EFLImpudence]

Just to clear up the shower Class I/II thing... Showers are usually Class I with Class II construction. There has to be double or reinforced insulation between live parts and the accessible plastic cover.

There is nothing between the live parts and the cover in a shower apart from air.

This is usually provided by the cover itself, the air between the cover and the live parts or a combination of the two.

Is that official?

Surely most things have air between the live parts and the outer cover.


Double insulated appliances, Class II, are not and must not be earthed.

 

[JohnW2]

Double insulated appliances, Class II, are not and must not be earthed.

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?

Kind Regards, John

 

[EFLImpudence]

Double insulated appliances, Class II, are not and must not be earthed.

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?

Because the double insulation is considered protection superior to earthing (which, in itself, is not a good thing) when the metal case may become live.

 

[JohnW2]

Because it (415.2) states extraneous and exposed-c-ps.

You've rather lost me. When do you think that the requirement of 710.415.2 that SB has to be connected to CPCs does apply, then?

When there are exposed-c-ps present.

As I've said many times, that would make electrical sense, but I really am not convinced that is what the words of the regs actually say. They seem pretty clear in saying that SB must be connected to the terminals of the CPCs "of all circuits" supplying equipment in the location but, if one were being logical, there's no obvious point in connecting to the CPC of a circuit if it is not associated with an exposed-c-p in the location.

Maybe it's a question of the "plumbers' cross-bonding" (just joining extraneous-c-ps, without connecting to anything else) of which you seem to approve not actually qualifying, as far as the regs are concerned, as "supplementary bonding" (because of the lack of connection to CPCs)?

Kind Regards, John

 

[JohnW2]

Double insulated appliances, Class II, are not and must not be earthed.

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?

Because the double insulation is considered protection superior to earthing (which, in itself, is not a good thing) when the metal case may become live.

But that's just an argument for not 'unnecessarily' earthing anything, including baths, doorknobs and spoons, not only metal Class II items - so I don't really understand the "must not be earthed" - "does not need to be earthed" or even "would be better not earthed" might be more understandable.

There's also the fact that double/reinforced insulation is not 'foolproof' - so earthing the metal casing of a Class II item could be argued to be 'even safer.

Kind Regards, John

 

[EFLImpudence]

Maybe it's a question of the "plumbers' cross-bonding" (just joining extraneous-c-ps, without connecting to anything else) of which you seem to approve not actually qualifying,

Well, not really.
That connects two pipes which are already connected by the boiler.
I am talking about pipes which may have quite a high impedance between them.

as far as the regs are concerned, as "supplementary bonding" (because of the lack of connection to CPCs)?

That depends on how it's read.
Cannot the definition of equipotential bonding, in part 2, apply just to the extraneous-c-ps.
Supplementary just means additional.

 

[JohnW2]

Maybe it's a question of the "plumbers' cross-bonding" (just joining extraneous-c-ps, without connecting to anything else) of which you seem to approve not actually qualifying,

Well, not really. That connects two pipes which are already connected by the boiler. I am talking about pipes which may have quite a high impedance between them.

As we've discussed before, this is very hypothetical. In practice, there are really only two possibilities for the impedance between two pipes - 'very low' (near zero), if they are parts of a metal-connected plumbing system or 'incredibly high', if one or both pipes is/are 'floating', because of lack of connection, or only plastic connection, between them.

Kind Regards, John

 

[EFLImpudence]

If near zero then they will not require bonding but it could be higher than required due to plastic fittings/lengths causing the connection to be only via two separate CPCs.

Are you saying it is not necessary to check?

 

[JohnW2]

If near zero then they will not require bonding but it could be higher than required due to plastic fittings/lengths causing the connection to be only via two separate CPCs. Are you saying it is not necessary to check?

What I don't understand about your tests (which are an adaptation of those described in 415.2.2 for assessment of the adequacy of SB) is how you would actually apply/interpret them in relation to just two pipes (in the absence of RCD protection).

As you know, the whole point of 415.2.2 is to ensure that the pd between two parts cannot exceed 50V before a protective device operates, and hence depends upon the "Ia" of "the protective device". However, if all you have to deal with are two pipes, which protective device are you going to use for that calculation? If there is 30mA RCD protection, then that's easy - but in that case there would very probably not be a need for SB, anyway!! In the absence of an RCD (such that SB is required)- would you calculate on the basis of the B6 lighting MCB, the B45/50 shower one, or what? ... and why?

Kind Regards, John

 

[EFLImpudence]

Not really sure.
I just have in mind the 'tingles'.

Are you saying it is not necessary to check?

 

[JohnW2]

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

Not necessarily - 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.

Kind Regards, John

 

[Chris61]

That's interesting, but I'm not sure that I understand! If they are have "Class II construction", with double or reinforced insulation, why are they not Class II?

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

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.

Chris61 wrote:
Just to clear up the shower Class I/II thing... Showers are usually Class I with Class II construction. There has to be double or reinforced insulation between live parts and the accessible plastic cover.

There is nothing between the live parts and the cover in a shower apart from air.

What I meant was the either the air between the enclosure and the live parts must provide the reinforced insulation or the enclosure itself does. insulation systems in an appliance are a topic on their own...

Quote:
This is usually provided by the cover itself, the air between the cover and the live parts or a combination of the two.

Is that official?

Surely most things have air between the live parts and the outer cover.

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

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