Under floor heating system problem

[North]

Response from the manufacturer:
Thank you for your email, the 200w/m2 heat film system does not have an earth and is double insulated and CE approved to meet British, European and International standards.

The film would not work with an earth cable as it works on radiant heat technology.

 

[SimonH2]

That's about what I got, and I've replied asking how it complies with 753.411.3.2 etc. As to working on radiant technology, all I'll say is "Hmm.."

 

[ban-all-sheds]

Class II items don't have exposed-c-ps.

Indeed not.

So a Class II heating unit would be delivered without exposed-conductive-parts.

Does that mean that Class II ones don't require the grid?

How can it when 753.411.3.2 says "In the case of heating elements which are delivered from the manufacturer without exposed-conductive-parts, a suitable conductive covering, for example, a metal grid with a spacing of not more than 30mm, shall be provided on site as an exposed-conductive-part above the floor heating elements ... and connected to the protective conductor of the electrical installation."?

 

[EFLImpudence]

753.411.3.2 states RCDs shall be used as the disconnecting device and that these items supplied without exposed-c-ps - it doesn't say Class II - shall be covered with an earthed metal grid.
753.415.1 states that Class II items shall be provided with additional protection of RCD.
Does that mean that Class II ones don't require the grid?

No, I think it means that the regs have changed, and 753.415.1 is now redundant.

But it does not say that; 753.411.3.2 says where the heating units are delivered without suitable conductive covering.

We have "All devices must hve RCD ..." and "some specific class of device must have RCD ..." - the latter is redundant since that specific class of device is a subset of "all devices". My guess is that in a previous version, RCD protection was only required for Class II devices.

Bearing in mind that the requirements for a suitable conductive covering - maximum grid spacing of 30mm, it clearly is not intended for protection from penetration by screws/nails but for ADS should the conductor become exposed.
This is not the case for Class II items.

Given the number of "The protective measure of <something> is not permitted" statements, I wonder if "Class II" is not actually permitted as a protection method any more ?

It does not say it.

Edit: Specifically, given that one of the primary risks is going to be penetration by the likes of screws and nails, "Class II" construction is going to be pretty meaningless as a method of protection against shock.

Is it? In the floor? As above.

Moreover, if the heating mat/film has a metallic covering but is Class II, then putting a screw through it could well make the whole floor live, not just the screw.

I do not follow.
The company does offer mats with a metallic covering which, obviously must be earthed and RCD protected.

The mat the OP has bought does not have a covering and the manufacturer says it is Class II. It also has to have RCD protection.

 

[ban-all-sheds]

The mat the OP has bought does not have a covering and the manufacturer says it is Class II.

And what does 753.411.3.2 say about that?

 

[EFLImpudence]

How can it when 753.411.3.2 says "In the case of heating elements which are delivered from the manufacturer without exposed-conductive-parts, a suitable conductive covering, for example, a metal grid with a spacing of not more than 30mm, shall be provided on site as an exposed-conductive-part above the floor heating elements ... and connected to the protective conductor of the electrical installation."?

Can't fault the logic.

Do you agree that the spacing requirement indicates the grid is not for penetration protection but ADS ^ and this is not required for Class II items?

Edit - ^ should the conductor become exposed.

 

[ban-all-sheds]

Do you agree that the spacing requirement indicates the grid is not for penetration protection but ADS

Seems reasonable. It clearly cannot be for mechanical protection.

and this is not required for Class II items?

No, I don't agree with that wrt Class II UFH. Although I am quite prepared to change my mind when I am shown where 753.411.3.2 says that a suitable conductive covering does not have to be provided on site if the heating units are Class II.

 

[ban-all-sheds]

Given what has happened so many times before, can we PLEASE not have people "interpreting" what the regulations say because they simply don't want them to mean what they actually do say.

There is no engineering reason why a conductive layer cannot be provided. I can understand why people might not want to, but not wanting to does not justify "interpreting" the regulations in order to come up with a "meaning" or "intention" which happens to match that desire.

 

[EFLImpudence]

and this is not required for Class II items?

No, I don't agree with that wrt Class II UFH. Although I am quite prepared to change my mind when I am shown where 753.411.3.2 says that a suitable conductive covering does not have to be provided on site if the heating units are Class II.

I did not mean it was not required by the Regulation but as it is supposedly Class II it is not really needed.

The single DI conductor cannot overload, short circuit or fault to earth so is unlikely to become exposed.

 

[SimonH2]

But it does not say that; 753.411.3.2 says where the heating units are delivered without suitable conductive covering.

Oops, teach me for trying to bash a quick reply in before breakfast

Well had a reply back, enclosing a letter from the manufacturer explaining how it complies. If I understand this forum properly it should be attached.
Personally, I can't see where it addresses 753.411.3.2

But, I also wonder about the bit where the product itself is not DI, it only becomes DI when the plastic sheet has been laid on top. As I recall the installation instructions, it says this should be installed, but does not mention the significance in terms of electrical safety. I can't help thinking that some people might be tempted to leave it out, not knowing it's importance.

 

[JohnW2]

Class II items don't have exposed-c-ps.

Quite so, at least per the BS7671 definition thereof. I think confusion arises because Class II items can (and sometimes do) have 'exposed parts which are made of conductive materials', which is a remarkably similar phrase!

Yes, but not in the electrical definition sense.

That's what I wrote, and you quoted ("in the electrical sense" = "per the BS7671 definition").

In another thread you recently wrote that some manufacturers say that Class II equipment 'must not be earthed'

Did I say "some"?

You didn't - but I think it's appropriate since MIs of some Class II equipment is silent about earthing, and others say that an earth is "not required", or something like that.

but what does that mean? What is it that 'must not be earthed'.

A CPC must not be connected to the appliance.

That much is obvious - but I was asking what part of the appliance the CPC 'must not be connected to'.

If it happens to have an outer 'exposed part which is made of conductive material' what harm can possibly come from earthing it ... (other than the general undesirability of 'unnecessarily earthing' anything)??

There you go. .... Things are better unearthed unless they have to be - these parts don't have to be.

By definition, Class II equipment does not need any part of it to be earthed. You and I (and probably a good few others) believe that "things are better off" (environment is potentially safer) if one does not unnecessarily earth touchable metal (whether that is part of something electrical, or something non-electrical like a metal bath).

However, there is no regulatory 'prohibition' of "unnecessarily earthing exposed metal" (imagine what EICRs would look like if there were!!), so the manufacturers have seemingly just made up this "must not....". If touching the outer casing of an item is safe by virtue of it being Class II, from the point-of-view of the equipment it does not become less safe if one earths the outer covering (if conductive). If (per stillp's suggestion when we last discussed this) one really believed that such earthing could theoretically have some detrimental effect on the equipment, then the MIs would surely have to prohibit their class II equipment ever coming in contact with anything earthed?

Kind Regards, John

 

[SimonH2]

Hmm, a look on Flexel's web site shows :
http://www.flexelinternational.com/products-ecofilm-set - mentions 5m cold tails
And the installation instructions (http://www.flexelinternational.com/files/documents/ecofilmset_install_diagrams_june_2010.pdf) also talk about doing all the joints in a box in the wall - nothing about crimping connections under the floor. Though I suspect that other manufacturers buy the film in bulk and make up their own products.
Also doesn't mention the electrical significant of the overlay sheet.

 

[EFLImpudence]

However, there is no regulatory 'prohibition' of "unnecessarily earthing exposed metal" (imagine what EICRs would look like if there were!!),

There is no regulatory prohibition of lots of things we don't do although requiring earthing of exposed-c-ps (electrical definition) does in effect not require earthing of parts which are not exposed-c-ps (electrical definition).
There is no regulatory prohibition of earthing spoons.

so the manufacturers have seemingly just made up this "must not....".

Would you rather they said "Please, please don't"?

If touching the outer casing of an item is safe by virtue of it being Class II, from the point-of-view of the equipment it does not become less safe if one earths the outer covering (if conductive).

Yes, it does. I don't know why you keep saying this.

If (per stillp's suggestion when we last discussed this) one really believed that such earthing could theoretically have some detrimental effect on the equipment,

Yet again - it has nothing to do with detrimental effects on the equipment; it is detrimental to personal safety.

then the MIs would surely have to prohibit their class II equipment ever coming in contact with anything earthed

How can manufacturers prohibit anything?

If you want to earth your drill; carry on.

 

[JohnW2]

There is no regulatory prohibition of lots of things we don't do although requiring earthing of exposed-c-ps (electrical definition) does in effect not require earthing of parts which are not exposed-c-ps (electrical definition). There is no regulatory prohibition of earthing spoons.

Exactly. That's why there is no regulatory basis for saying that (when it's possible!) Class II equipment "must not be earthed".

so the manufacturers have seemingly just made up this "must not....".

Would you rather they said "Please, please don't"?

If they feel the need to say anything, I would problem prefer them to say that earthing was not needed/required.

If touching the outer casing of an item is safe by virtue of it being Class II, from the point-of-view of the equipment it does not become less safe if one earths the outer covering (if conductive).

Yes, it does. I don't know why you keep saying this.

If you don't understand why I keep saying it, you can't fully understand what I'm saying - so perhaps I'm not being clear enough. What I'm trying to say is that (ignoring stillp's theoretical argument), the equipment itself cannot become any less safe by virtue of the touchable parts being earthed.

You and I may feel that the environment would become less safe as a consequence of unnecessarily increasing the amount of earthed metal around - but that would be just as true if we were talking about baths, metal shelves or a metal tool cabinet - it's nothing to do with the equipment in question being 'electrical'.

If (per stillp's suggestion when we last discussed this) one really believed that such earthing could theoretically have some detrimental effect on the equipment, then the MIs would surely have to prohibit their class II equipment ever coming in contact with anything earthed

How can manufacturers prohibit anything?

They can't - but they can, and often do, say "Must not..." in their instructions - so, if they believed that earthing the outer covering of their Class II equipment could have a detrimental effect on that equipment, then they could (and probably should) also say "Must not ...." in relation to allowing the item to come in contact with anything earthed.

Kind Regards, John

 

[EFLImpudence]

If you don't understand why I keep saying it, you can't fully understand what I'm saying - so perhaps I'm not being clear enough. What I'm trying to say is that (ignoring stillp's theoretical argument), the equipment itself cannot become any less safe by virtue of the touchable parts being earthed.

Not by the workings of that equipment, no - but because of other occurrences.
Is that not the same difference?

Like saying you aren't more likely to drown because of unnecessarily earthing a bath - but as it makes it environmentally (electrically) less safe, why argue for it?

You and I may feel that the environment would become less safe as a consequence of unnecessarily increasing the amount of earthed metal around - but that would be just as true if we were talking about baths, metal shelves or a metal tool cabinet - it's nothing to do with the equipment in question being 'electrical'.

Who has said it is?

They can't - but they can, and often do, say "Must not..." in their instructions - so, if they believed that earthing the outer covering of their Class II equipment could have a detrimental effect on that equipment, then they could (and probably should) also say "Must not ...." in relation to allowing the item to come in contact with anything earthed.

I have mentioned it before but there are Class II 12V lights which use the metal bodywork as the return path for the 12V.
I presume "must not" would be appropriate for this.