No earth cable on light fitting

[EFLImpudence]

Don't all shower pumps come with plastic/nylon pipes for connection?
They would be very noisy connected to fixed copper pipes.




I wouldn't be surprised to find John and PBC standing in the next election.

From a subject like not connecting a CPC to Class II lights being simple to accept and reason, we have progressed to the possibility that such a simple instruction may be a mistake in the manufacturers' instructions because sometimes there could be an error in the instructions for any appliance no matter how complicated they may be.



Instead, let's discuss the instruction FOR the connection of a CPC to a Class I light fitting and see if we can come up with a list of ideas why this may be a bad thing to do and a mistake by the manufacturer.

 

[JohnW2]

Touche! No, it's from a market leader. However as I said I don't have the instructions, which might add clarity.

Fair enough.

I'm sure that I don't have to tell you that that is VERY different from saying "must not be earthed".

Quite. There is no provision for earthing though.

I suppose there wouldn't be if they are saying that earthing is 'unnecessary' - but the implication is surely that they are not saying that "it must not be earthed"?

Kind Regards, John

 

[JohnW2]

Instead, let's discuss the instruction FOR the connection of a CPC to a Class I light fitting and see if we can come up with a list of ideas why this may be a bad thing to do and a mistake by the manufacturer.

I think you may be missing the point.

We all know (and I imagine agree with) the compelling electrical reasons for earthing the exposed-c-ps of a Class I item ('compelling' meaning the the reasons for earthing greatly outweigh the reasons for not earthing) - so your 'list of ideas' would hopefully be empty.

In contrast, I don't think any of us know of any good (let alone compelling) electrical reasons for not earthing exposed c-ps of Class II items (other than those which would apply equally to worktops, baths & window frames etc. - none of which come with "do not earth" instructions). Stillp says that it 'could case the item to fail' but, unless he can propose a credible explanation, I cannot see how anything can be 'safe' if it may become 'unsafe' if the outer case comes in contact with earth.

Kind Regards, John

 

[JohnW2]

Don't all shower pumps come with plastic/nylon pipes for connection? They would be very noisy connected to fixed copper pipes.

Most of the ones I've seen come with short flexible hoses enclosed in (conductive) metal braided coverings and sometimes metal unions, which are not infrequently then connected to fixed copper pipework. They are, of course, only in contact with parts of the pump made of insulating materials but, according to stillp, that does not prevent a hazard arising.

Kind Regards, John

 

[stillp]

unless he can propose a credible explanation

Credible to whom? An electrical engineer with experience in FMEA?

 

[JohnW2]

unless he can propose a credible explanation

Credible to whom? An electrical engineer with experience in FMEA?

Credible to anyone who can understand the explanation. Unless/until we know what the explanation is, we can't even guess as to whether it would be credible to anyone.

Kind Regards, John

 

[PBC_1966]

Instead, let's discuss the instruction FOR the connection of a CPC to a Class I light fitting and see if we can come up with a list of ideas why this may be a bad thing to do and a mistake by the manufacturer.

Well, leaving aside issues about what the manuacturer says and whether the product is somehow so badly designed and made that having earth potential on the casing might somehow prejudice its operation or longevity, if earthing the metal case of a class II device introduces the (very small) risk of that case becoming live due to some external fault, then exactly the same argument applies to earthing the casing of a class I device (which is where we started this particular debate several pages ago).

If you could look at some class I device and deduce that the chances of an internal fault making the casing live were less than the chances of some external fault doing the same if it were left unearthed, wouldn't that be just as much an argument for leaving the class I casing unearthed as for the class II casing?

I have several older devices here (household appliances and test equipment) which are not double insulated in the modern sense, but which have metal casings and only a 2-conductor supply cord. But looking at the way they're made, I actually feel more comfortable with the unearthed casings of those than with the unearthed casings of many modern double-insulated things I've examined (such as that desk lamp I mentioned earlier).

We have two mutually exclusive methods for protecting against two different types of fault. We can play the numbers game on what we think might be the more likely thing to happen and decide on that basis. Or perhaps we need an electronically controlled crystal ball? Let's just make sure it has no exposed metalwork!

 

[JohnW2]

If you could look at some class I device and deduce that the chances of an internal fault making the casing live were less than the chances of some external fault doing the same if it were left unearthed, wouldn't that be just as much an argument for leaving the class I casing unearthed as for the class II casing?

It would - BUT, unless the Class I item were in fact effectively Class II, then I don't think that scenario would ever arise. If the Class I item did not have 'double/reinforced insulation' (or some similar/equivalent) which would qualify it as Class II, it is extremely unlikely that it would ever be true that "the chances of an internal fault making the casing live were less than the chances of some external fault doing the same if it were left unearthed", isn't it?

Kind Regards, John

 

[stillp]

the product is somehow so badly designed and made that having earth potential on the casing might somehow prejudice its operation or longevity,

Why would that necessarily be bad design?

 

[stillp]

I've recently been dealing with a case where a person suffered life-changing injuries because someone thought he knew better than the manufacturer of an item.

 

[JohnW2]

the product is somehow so badly designed and made that having earth potential on the casing might somehow prejudice its operation or longevity,

Why would that necessarily be bad design?

Because it implies that the design is such that, under some circumstances, there can be a significant 'electrical connection' of some sort between allegedly insulated live parts within and parts of the item that a user is meant to be able to touch safely?

Kind Regards, John

 

[stillp]

Only in the event of two failures. The same is true of a Class I item.

 

[JohnW2]

I've recently been dealing with a case where a person suffered life-changing injuries because someone thought he knew better than the manufacturer of an item.

I don't doubt it, but that could relate to absolutely anything (the 'someone' might just have been being plain silly, and ignoring obviously crucial safety advice from the manufacturer), and hence really means nothing in relation to the general discussion.

Furthermore, if it were possible to look hard enough, one would probably be able to find at least a few cases in which people have avoided serious injury because they did know better than the manufacturer.

Kind Regards, John

 

[PBC_1966]

Only in the event of two failures.

You mean both parts of the double insulation fail?

 

[PBC_1966]

Furthermore, if it were possible to look hard enough, one would probably be able to find at least a few cases in which people have avoided serious injury because they did know better than the manufacturer.

Undoubtedly. But we tend not to hear about injuries which never happened, so who knows how many such incidents may have been avoided because somebody ignored the manufacturer's instructions?