Electric under floor heating, and BS 7671

[RF Lighting]

I was presented with an underfloor heating system which was installed by the tiler.

I was asked to connect it up, and provide the certificate. On inspection of the cold tails, they do not contain a CPC, and it transpires that the heating element does not incorporate an earthed metallic screen, so I said I was not happy to connect it without certainly some more investigation.

The manufacturers said on the phine it was fine to go ahead and connect their product without and provision for earthing the product. I asked for something in writing, and they have sent the following response:

Now I'm still not satisfied that regulation 753.411.3.2 is complied with, and therefore the installation can't be signed off.

The regulation clearly states: "RCDs with a rated residual current not exceeding 30mA shall be used as disconnecting devices. In the case of heating units which are delivered from the manufacturer without exposed-conductive-parts, a suitable conductive covering, for example, a grid with a spacing of not more than 30 mm, shall be provided on site as an exposed-conductive-part above the floor heating elements or under the ceiling heating elements, and connected to the protective conductor for the electrical installation.

There is no mention of it being permissible to ingore the above regulation if the heating element is a class II product.

I am just preparing my reply to them, and wanted to make sure I'm not missing something blindingly obvious.

Thoughts?

 

[JohnW2]

I am just preparing my reply to them, and wanted to make sure I'm not missing something blindingly obvious. Thoughts?

FWIW, the brief thoughts of an 'outsider' ... in a nutshell, with the regs as they are written, I'm sure you are not missing anything at all.

Although you're obliged to work to the regs 'as they are written', I am tempted to wonder whether they perhaps forgot to say that 753.411.3.2 applied only to Class I products - since, as everything is actually written, 753.415.1 (specifically about Class II products), doesn't mention the need for an earthed grid.

Kind Regards, John

 

[OwainDIYer]

How can you verify the site applied insulation if it's already been tiled over?

 

[EFLImpudence]

Agree with Owain but -

753.415.1 does say 'Class II construction or equivalent insulation...' so it looks as if they may be correct but you still cannot see it.

 

[JohnW2]

753.415.1 does say 'Class II construction or equivalent insulation...' so it looks as if they may be correct ...

Yes, but as I said (on re-reading, probably not very clearly!), with the regs as written, 753.411.3.2 (with it's requirement for an earthed grid) also applies (in addition to 735.415.1) even if it is of 'Class II or equivalent construction' - which is why I wondered whether they had perhaps 'forgotten' to mention that 735.411.3.2 only applied to Class I.

Kind Regards, John

 

[EFLImpudence]

753.415.1 does say 'Class II construction or equivalent insulation...' so it looks as if they may be correct ...

Yes, but as I said (on re-reading, probably not very clearly!), with the regs as written, 753.411.3.2 (with it's requirement for an earthed grid) also applies (in addition to 735.415.1) even if it is of 'Class II or equivalent construction'

What, then, is the need for 753.415.1?

which is why I wondered whether they had perhaps 'forgotten' to mention that 735.411.3.2 only applied to Class I.

Do you men the regulations have forgotten?

I don't know then.
A Class I item without exposed-conductive-parts must only have one layer of insulation.
A Class II item should/must not be earthed but also will have no exposed-c-ps.

 

[JohnW2]

Yes, but as I said (on re-reading, probably not very clearly!), with the regs as written, 753.411.3.2 (with it's requirement for an earthed grid) also applies (in addition to 735.415.1) even if it is of 'Class II or equivalent construction'

What, then, is the need for 753.415.1?

which is why I wondered whether they had perhaps 'forgotten' to mention that 735.411.3.2 only applied to Class I.

Do you men the regulations have forgotten?

Indeed, that's what I was pondering - that those who wrote the regs perhaps 'forgot' to include some words indicating that 735.411.3.2 only applies to Class I, just as 753.415.1 only applies to Class II. The totality of the two regs would then make sense (to me). As it stands, the requirement for the earthed grid appears to apply regardless of whether the product is Class I or II - which seems rather 'odd', to say the least!

Kind Regards, John

 

[ericmark]

735.411.3.2 was not in BS7671:2008 (At least I can't find it.) only in BS7671:2008 Amendment 1 so that document they have sent you is out of date.

 

[JohnW2]

735.411.3.2 was not in BS7671:2008 (At least I can't find it.) only in BS7671:2008 Amendment 1 so that document they have sent you is out of date.

Eric, if you are literally looking for 735.411.3.2, that does not exist, and never has existed; indeed there is no Section 735.

What you should be looking for is 753.411.3.2, which was present in the original BS7671:2008 in exactly the same form as in the 2011 Amendment.

Kind Regards, John

 

[vad25]

I was presented with an underfloor heating system which was installed by the tiler.

This installation can't be certified by tiler.
Electrical underfloor heating system is under part P building regulations.

 

[EFLImpudence]

All domestic (is it?) electrical work comes under part P but this type of work is no longer notifiable.

Therefore it could be certified by the tiler but I suppose he doesn't do electrical work - fair enough.

Therefore, he or the owner should have involved an electrician during the installation but I assume the tiler could still sign the construction part of the certificate.

 

[EFLImpudence]

As for the regulations -


Even ufh elements which incorporate an earthed metallic screen still do not have any exposed-c-ps.


As this ufh is only deemed ClassII by the addition of the insulating film, it must therefore actually be, in itself, Class I - not having double insulation - and without exposed-c-ps.

So, are the regulations saying that either an earthed grid OR an insulating film can be used?

 

[JohnW2]

Indeed, that's what I was pondering - that those who wrote the regs perhaps 'forgot' to include some words indicating that 753.411.3.2 only applies to Class I, just as 753.415.1 only applies to Class II. The totality of the two regs would then make sense (to me). ...

The other odd thing about 753.411.3.2 is its actual wording, which says:

In the case of heating units which are delivered from the manufacturer without exposed-conductive-parts, a suitable conductive covering, for example, a grid with a spacing of not more than 30 mm, shall be provided on site as an exposed-conductive-part above the floor heating".

One imagines that what they really meant was something like "...delivered from the manufacturer without an adequate metallic screen which can be earthed...". As written, an additional earthed metallic grid would not be required if the unit had any 'exposed-conductive parts' - which theoretically could be limited in location (e.g. just in the vicinity of the cable entry/exit), or perhaps a grid with larger than 30mm spacing. Regardless of whether my previous speculation about this reg is correct, this therefore seems to me to be another example of a less-than-ideally worded reg.

Kind Regards, John

 

[JohnW2]

As for the regulations - Even ufh elements which incorporate an earthed metallic screen still do not have any exposed-c-ps. ... As this ufh is only deemed ClassII by the addition of the insulating film, it must therefore actually be, in itself, Class I - not having double insulation - and without exposed-c-ps. ... So, are the regulations saying that either an earthed grid OR an insulating film can be used?

As I've said, given the actual wording of the regs, in the absence of any qualifications in 753.411.3.2, any unf "without exposed-conductive-parts" (which would obviously include Class II units) needs the additional earthed grid. That's why I wondered whether that reg may have been intended (but not written!) to apply only to Class I products.

Kind Regards, John.

 

[bernardgreen]

I just did a search for the word "Earth" in the Flexel installation instructions

http://www.flexelinternational.com/files/documents/ecofilmset_install_diagrams_june_2010.pdf

The search could not find the word "earth" in that document.

Common sense ( my version ) and some experience would suggest that in the absence of any grounded mesh above the heating system any penetration of moisture that reaches the live element would not trip any safety device until the moisture on the surface has an electrical path to ground. That path could be via a person's foot, leg, heart, arm hand, water tap.