I am in the process of insulating under our kitchen floor, the plan being to fit the Celotex between the joists and fill any gaps around the edge with PU foam. However, some of these gaps also have cables passing through so just to check does PU foam react like polystyrene with PVC? Secondly, does passing through 100mm of insulation have any significant effect on the cable ratings?

Richard

On 04/10/2020 23:00, Tricky Dicky wrote:

I am in the process of insulating under our kitchen floor, the plan
being to fit the Celotex between the joists and fill any gaps around
the edge with PU foam. However, some of these gaps also have cables
passing through so just to check does PU foam react like polystyrene
with PVC?

No, it does not leach the plasticiser in the way EPS does.

Secondly, does passing through 100mm of insulation have any
significant effect on the cable ratings?

Yes, you would need to de-rate the cable by a factor of 0.78 [1]

So take the column C "clipped direct" rating for the cable :

http://wiki.diyfaq.org.uk/index.php/Cables#Cable_Sizes

and multiple by the de-rating factor as well as any others that apply
(see the article below for full details)

So for example a 2.5mm^2 T&E with a clipped direct rating of 27A would
be reduced to 27 x 0.78 = 21.06A (which is only just high enough for use
in a 32A ring circuit)



[1]
http://wiki.diyfaq.org.uk/index.php/..._in_insulation


--
Cheers,

John.

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On 04/10/2020 23:00, Tricky Dicky wrote:
I am in the process of insulating under our kitchen floor, the plan
being to fit the Celotex between the joists and fill any gaps around
the edge with PU foam. However, some of these gaps also have cables
passing through so just to check does PU foam react like polystyrene
with PVC? Secondly, does passing through 100mm of insulation have any
significant effect on the cable ratings?

Richard


Should also have added, that it does depend a bit on what you mean bu
"in insulation". The worst case is literally that - surrounded on all
sides by insulation. Some cases are less onerous however - say wan its a
cable against a conductive surface like a wall or plasterboard, with an
insulation covering. See the installation methods section he

http://wiki.diyfaq.org.uk/index.php/...lation_Methods


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 5 Oct 2020 at 02:20:01 BST, "John Rumm"
wrote:

On 04/10/2020 23:00, Tricky Dicky wrote:
I am in the process of insulating under our kitchen floor, the plan
being to fit the Celotex between the joists and fill any gaps around
the edge with PU foam. However, some of these gaps also have cables
passing through so just to check does PU foam react like polystyrene
with PVC? Secondly, does passing through 100mm of insulation have any
significant effect on the cable ratings?

Richard


Should also have added, that it does depend a bit on what you mean bu
"in insulation". The worst case is literally that - surrounded on all
sides by insulation. Some cases are less onerous however - say wan its a
cable against a conductive surface like a wall or plasterboard, with an
insulation covering. See the installation methods section he

http://wiki.diyfaq.org.uk/index.php/...lation_Methods

Thanks - I did something similar recently, but 50mm celotex, and routed the
cables through the floor/insulation using some flexible c.3cm quite heavy duty
cable tidy/trunking fixed with foam.

The 'worst case' was 4 cables, and while there could be quite a lot going on
(oven, kettle, toaster etc), my method was reasonably neat and seemed like it
might be effective. But not, I see now, one of the reference methods. I've yet
to finish skirting etc and could easily take out the trunking and clip the
cables to the joist a cm or so apart - might that be better?

--
Cheers, Rob

On 05/10/2020 06:23, RJH wrote:
On 5 Oct 2020 at 02:20:01 BST, "John Rumm"
wrote:

On 04/10/2020 23:00, Tricky Dicky wrote:
I am in the process of insulating under our kitchen floor, the plan
being to fit the Celotex between the joists and fill any gaps around
the edge with PU foam. However, some of these gaps also have cables
passing through so just to check does PU foam react like polystyrene
with PVC? Secondly, does passing through 100mm of insulation have any
significant effect on the cable ratings?

Richard


Should also have added, that it does depend a bit on what you mean bu
"in insulation". The worst case is literally that - surrounded on all
sides by insulation. Some cases are less onerous however - say wan its a
cable against a conductive surface like a wall or plasterboard, with an
insulation covering. See the installation methods section he

http://wiki.diyfaq.org.uk/index.php/...lation_Methods

Thanks - I did something similar recently, but 50mm celotex, and routed the
cables through the floor/insulation using some flexible c.3cm quite heavy duty
cable tidy/trunking fixed with foam.

The 'worst case' was 4 cables, and while there could be quite a lot going on
(oven, kettle, toaster etc), my method was reasonably neat and seemed like it
might be effective. But not, I see now, one of the reference methods. I've yet
to finish skirting etc and could easily take out the trunking and clip the
cables to the joist a cm or so apart - might that be better?

Don't worry too much about matching the method, there are a much larger
number of installation methods documented in the full version of BS7671.
Its more the principle to follow.

So cable grouping is one - note that its based on the number of circuits
rather than the number of cables. Also if a cable is expected to carry
less than 30% of its grouped current rating, then you can ignore it from
the count of grouped cables when working out the effects on other cables.

Spacing cable helps. Having them clipped to a thermally conductive
surface helps - even if they are covered in insulation.



--
Cheers,

John.

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\================================================= ================/

Unless the cables are stressed already, I'd not think it would.
Don't know about reactions, but unless it outgases a lot, I'd imagine the
space under there would mean it was pretty diluted, others may feel
differently, we never had such worries in my day... I feel like leaning on
an old gnarled walking stick near a farm gate looking into the distance...
grin.
Brian

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"Tricky Dicky" wrote in message
...
I am in the process of insulating under our kitchen floor, the plan being to
fit the Celotex between the joists and fill any gaps around the edge with PU
foam. However, some of these gaps also have cables passing through so just
to check does PU foam react like polystyrene with PVC? Secondly, does
passing through 100mm of insulation have any significant effect on the cable
ratings?

Richard

On Monday, 5 October 2020 at 08:55:45 UTC+1, Brian Gaff (Sofa) wrote:
Unless the cables are stressed already, I'd not think it would.
Don't know about reactions, but unless it outgases a lot, I'd imagine the
space under there would mean it was pretty diluted, others may feel
differently, we never had such worries in my day... I feel like leaning on
an old gnarled walking stick near a farm gate looking into the distance...
grin.
Brian

--
--
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Tricky Dicky" wrote in message
...
I am in the process of insulating under our kitchen floor, the plan being to
fit the Celotex between the joists and fill any gaps around the edge with PU
foam. However, some of these gaps also have cables passing through so just
to check does PU foam react like polystyrene with PVC? Secondly, does
passing through 100mm of insulation have any significant effect on the cable
ratings?

Richard
Thanks John, thinking back now I should have extended the capping that extra 100mm. On the safe side I will either do what Rob did or block the PU foam from contacting the cables.

Richard

On Sun, 4 Oct 2020 15:00:43 -0700 (PDT), Tricky Dicky wrote:

... the plan being to fit the Celotex between the joists and fill any
gaps around the edge with PU foam. However, some of these gaps also have
cables passing through so just to check does PU foam react like
polystyrene with PVC?

Donno but I'd side step the issue by cutting the celotex to be a snug
push fit and simply taping any joints. Foamed in would make any
future access behind the insulation a right PITA.

--
Cheers
Dave.

"Dave Liquorice" Wrote in message:
On Sun, 4 Oct 2020 15:00:43 -0700 (PDT), Tricky Dicky wrote:

... the plan being to fit the Celotex between the joists and fill any
gaps around the edge with PU foam. However, some of these gaps also have
cables passing through so just to check does PU foam react like
polystyrene with PVC?

Donno but I'd side step the issue by cutting the celotex to be a snug
push fit and simply taping any joints. Foamed in would make any
future access behind the insulation a right PITA.


+1
--
Jimk


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

On Monday, 5 October 2020 at 09:58:17 UTC+1, Dave Liquorice wrote:
On Sun, 4 Oct 2020 15:00:43 -0700 (PDT), Tricky Dicky wrote:

... the plan being to fit the Celotex between the joists and fill any
gaps around the edge with PU foam. However, some of these gaps also have
cables passing through so just to check does PU foam react like
polystyrene with PVC?
Donno but I'd side step the issue by cutting the celotex to be a snug
push fit and simply taping any joints. Foamed in would make any
future access behind the insulation a right PITA.

--
Cheers
Dave.
Dave I have two joists very close to the wall where the cables are passing below the floor. On one I can do what you suggest and was going to use the PU to fill any gaps. On the other wall there is very little space, although I will try to do as on the other side but suspect the time saving element will be simply to PU the gap.

Richard

On Mon, 5 Oct 2020 08:19:27 +0100, John Rumm wrote:

Spacing cable helps. Having them clipped to a thermally conductive
surface helps - even if they are covered in insulation.

When I insulated the loft I ran all but one of the cables (lighting only)
across the boards - neater underneath but not as bad as onto exposed joists
as they're easier to avoid.
The one cable is on top of the insulation and directly under the chipboard.
All the others have ~75 mm in insulation; that and a 6A mcb should be OK.
Even if all of the LEDs were swapped out for 100W incandescent lamps it'd be
like a grill upstairs and unlikely to happen.
--
Peter.
The gods will stay away
whilst religions hold sway

On Mon, 5 Oct 2020 02:45:23 -0700 (PDT), Tricky Dicky wrote:

... does PU foam react like polystyrene with PVC?

Donno but I'd side step the issue by cutting the celotex to be a
snug
push fit and simply taping any joints. Foamed in would make any
future access behind the insulation a right PITA.

Dave I have two joists very close to the wall where the cables are
passing below the floor.

Think I'd still try and avoid the PU foam if at all possible and
loosely pack the joist/wall gap with some other insulation, rock or
sheep wool and tape over the top.

--
Cheers
Dave.

On 5 Oct 2020 at 08:19:27 BST, "John Rumm"
wrote:

On 05/10/2020 06:23, RJH wrote:
On 5 Oct 2020 at 02:20:01 BST, "John Rumm"
wrote:

On 04/10/2020 23:00, Tricky Dicky wrote:
I am in the process of insulating under our kitchen floor, the plan
being to fit the Celotex between the joists and fill any gaps around
the edge with PU foam. However, some of these gaps also have cables
passing through so just to check does PU foam react like polystyrene
with PVC? Secondly, does passing through 100mm of insulation have any
significant effect on the cable ratings?

Richard


Should also have added, that it does depend a bit on what you mean bu
"in insulation". The worst case is literally that - surrounded on all
sides by insulation. Some cases are less onerous however - say wan its a
cable against a conductive surface like a wall or plasterboard, with an
insulation covering. See the installation methods section he

http://wiki.diyfaq.org.uk/index.php/...lation_Methods

Thanks - I did something similar recently, but 50mm celotex, and routed the
cables through the floor/insulation using some flexible c.3cm quite heavy
duty
cable tidy/trunking fixed with foam.

The 'worst case' was 4 cables, and while there could be quite a lot going on
(oven, kettle, toaster etc), my method was reasonably neat and seemed like
it
might be effective. But not, I see now, one of the reference methods. I've
yet
to finish skirting etc and could easily take out the trunking and clip the
cables to the joist a cm or so apart - might that be better?

Don't worry too much about matching the method, there are a much larger
number of installation methods documented in the full version of BS7671.
Its more the principle to follow.

So cable grouping is one - note that its based on the number of circuits
rather than the number of cables. Also if a cable is expected to carry
less than 30% of its grouped current rating, then you can ignore it from
the count of grouped cables when working out the effects on other cables.

Spacing cable helps. Having them clipped to a thermally conductive
surface helps - even if they are covered in insulation.

Many thanks - you know your cables!

--
Cheers, Rob

On 05/10/2020 12:01, PeterC wrote:
On Mon, 5 Oct 2020 08:19:27 +0100, John Rumm wrote:

Spacing cable helps. Having them clipped to a thermally conductive
surface helps - even if they are covered in insulation.

When I insulated the loft I ran all but one of the cables (lighting only)
across the boards - neater underneath but not as bad as onto exposed joists
as they're easier to avoid.
The one cable is on top of the insulation and directly under the chipboard.
All the others have ~75 mm in insulation; that and a 6A mcb should be OK.
Even if all of the LEDs were swapped out for 100W incandescent lamps it'd be
like a grill upstairs and unlikely to happen.

Yup lighting circuits are unlikely to be a problem since the cable is
massively over-specced from a current carrying capability in most cases.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/