Under floor heating system problem

[North]

http://floor-heating.co.uk/heating-film/
My one is like this. It says "Vysa-Film heating elements do not have an earthed metallic sheath and may not be installed in a bathroom"
Do they mean that you "have" to install one?

 

[SimonH2]

I think their intension is that you don't install an earthed sheet/grid, judging from the later part of the same sentence which says "... as it is impractical to install an earthed metallic grid above them." That, as I read it, says it's not practical to install an earthed grid over the foil, and that's why you can't use it in a bathroom. If that is the case, then you also can't safely use it in any other room !

BTW - apologies if I missed it, but can you state exactly which product you bought, Living Heat have several with different terminations.

 

[ban-all-sheds]

You have to have one, no matter where it is installed - bathroom is irrelevant.

 

[North]

The one I purchased is this one:
http://www.livingheat.co.uk/Under-laminate-heating.html
The first one that you can see in the list (200W). Just to clarify it is going in the kitchen under wooden laminate floor

 

[ban-all-sheds]

Doesn't matter where it goes - you need an earthed screen above it.

 

[SimonH2]

http://www.livingheat.co.uk/Under-laminate-heating.html
The first one that you can see in the list (200W). Just to clarify it is going in the kitchen under wooden laminate floor

OK then, the installation instructions for that clearly show no earth (because it's so easy to put (eg) a screw through the floor and hit a live wire), so it is not safe if installed according to those instructions

Well I've fired off queries to both Living Heat and Floor Heating, lets see what they say Now, where did I put the popcorn ...

 

[North]

Me too! Just dropped the question to them. lets see who gets an answer first, Can you pass me the popcorn?

 

[johnny_t]

For what it's worth, I recently installed one of these systems - http://rayotec.com/electric-underfloor-heating-for-carpet - in my new extension. Works fine for my needs and the floor gets nice and toasty.

 

[SimonH2]

Not having an earthed layer above the mats, e.g. a metal grid with a spacing of not more than 30mm, is not allowed.

Can someone cite the reg on this ?
The first response has come back asking which reg I think is being breached, as they believe "Our understanding of all the UKregulations is that a Class II product such as this is fully compliant ..." (except for bathrooms etc).
I can see that 753.411.3.2 requires an overlying conductive covering - so I suppose they are arguing that they comply with this (by having an overlaid film), but by being Class II it doesn't need earthing.
Then in Part 2, it defines Exposed Conductive Part as "... can be touched and which is not normally live, but can which can become live when basic insulation fails". So I suppose the argument is that if there isn't a conductive foil or screen then one has to be added, but if it's there it has to be classes as an exposed conductive part even if the element is supposed to be Class II.
And then 411.3.1.1 says that "exposed conductive parts shall be connected to a protective conductor ..."

 

[EFLImpudence]

First of all - where does it say it is Class II?

 

[JohnW2]

Then in Part 2, it defines Exposed Conductive Part as "... can be touched and which is not normally live, but can which can become live when basic insulation fails". So I suppose the argument is that if there isn't a conductive foil or screen then one has to be added, but if it's there it has to be classes as an exposed conductive part even if the element is supposed to be Class II.

I've never really understood the concept of an exposed-c-p of a class II item. If the innards of the item is class 2, then it is deemed to be safe to touch the outside of those innards, so I don't see why additionally enclosing/covering it with something conductive renders that "conductive something" an exposed-c-p which represents a hazard if not earthed.

Kind Regards, John

 

[EFLImpudence]

I asked last Friday if this item was Class II. Not yet answered, I think.

I've never really understood the concept of an exposed-c-p of a class II item.

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

If the innards of the item is class 2, then it is deemed to be safe to touch the outside of those innards, so I don't see why additionally enclosing/covering it with something conductive renders that "conductive something" an exposed-c-p which represents a hazard if not earthed.

Quite.


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?

 

[JohnW2]

I've never really understood the concept of an exposed-c-p of a class II item.

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!

In another thread you recently wrote that some manufacturers say that Class II equipment 'must not be earthed' - but what does that mean? What is it that 'must not be earthed'. 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)??

Kind Regards, John

 

[EFLImpudence]

I've never really understood the concept of an exposed-c-p of a class II item.

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.

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

Did I say "some"?

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

A CPC must not be connected to the appliance.

If it happens to have an outer 'exposed part which is made of conductive material' what harm can possibly come from earthing it

As before - It may become live because of a fault elsewhere and
would provide a path to earth for a person touching it who may be receiving a shock.
Things are better unearthed unless they have to be - these parts don't have to be.

(other than the general undesirability of 'unnecessarily earthing' anything)??

There you go.

 

[SimonH2]

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. 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.

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 ?
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. 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.