Icynene and electrical wiring

[ProDave]

I have a customer considering insulating his new build with Icynene spray insulation.

 

So we started talking about wiring and service voids etc.

 

"Oh no there is no service void, you first fix before they spray the insulation."

 

Fine I say, but you will have to apply derating because the cables will end up encased in insulation.

 

Not the case says he, The Icynene rep says not.

 

Digging around their website finds this document http://www.uksprayfoam.co.uk/wp-content/uploads/Icynene-electrical-Wiring.pdf

 

Where it says wires encased in their insulation "will not cause the wire temperature to exceed safety limits"

 

I say sod that, as the electrical designer I will have to derate the cables which may end up with larger size cabling being used.

 

Are they giving bad advice?

 

Interresting to know what others who used Icynene (or similar) did? Did they do as they say, or did your electrian raise concerns and fit larger cables?

[Jeremy Harris]

Yes, they are giving advice that conflicts with BS7671, so they need to change it.

 

Their argument may be that Icynene foam doesn't react with PVC cable, which I'd guess it doesn't, and they've made the error of then assuming that nothing else needs to be considered as far as wiring is concerned.

 

Not sure I like the idea of embedding wiring directly in foam.  If there's no service void then I think I'd look to see if conduit or trunking could be used, if only to avoid the need to rip large areas of foam out if any changes are needed in future.

[ADLIan]

Might well be acceptable in Canada - not necessarily here! No expert on the electrical Regs but do they give any exclusions for particular types of insulation - I doubt it.

 

I'm with you ProDave

[ProDave]

I am not putting too much thought into the design just yet until I know for certain that is his chosen insulation.

 

Yes I would put the cables in PVC conduit, but that won't stop the need for derating.  

 

What really puts me off that is you need to be damned sure you have everything exactly where you want it at first fix time, which will be earlier in the build than the service void method.  I have tried to tell him there is nothing stopping him using Icynene without any cables, and then still battening to form a service void.

[PeterW]

I'd use 32mm waste pipe as conduit rather than normal 20/25mm as it will give you more space for bigger cables.

[ToughButterCup]

1 hour ago, JSHarris said:

Yes, they are giving advice that conflicts with BS7671, so they need to change it.

[...]

 

Why , why, why do companies even attempt to trade without even a cursory look at relevant guidelines? Why?

[Jeremy Harris]

33 minutes ago, AnonymousBosch said:

 

Why , why, why do companies even attempt to trade without even a cursory look at relevant guidelines? Why?

 

 

May be that some companies are just importing products from countries with different regulations?

 

The regs here haven't changed significantly for years with respect to cables in insulation.  This is from the current regs (BS7671:2018):

 

Quote

523.9  Cables In thermal Insulation

A cable should preferably not be installed in a location where it is liable to be covered by thermal insulation. Where a cable  is to be  run  in  a space to  which  thermal  insulation is  likely to be  applied it  shall,  wherever practicable, be fixed  in a  position  such  that  it  will  not  be covered  by  the  thermal  insulation.  Where fixing  in such  a  position  is impracticable the cross-sectional area of the cable shall be selected to meet the requirements of Chapter 43. 

Where necessary, the nature of the load (e.g. cyclic) and diversity may be taken into account.

For a cable installed in a thermally insulated wall or above a thermally insulated ceiling, the cable being in contact with a thermally conductive surface on one side, current-carrying capacities are tabulated in Appendix 4.

For a single cable likely to  be  totally surrounded  by  thermally  insulating material over a  length of 0.5m or more, the current-carrying capacity shall  be  taken,  in  the absence of more  precise information, as 0.5 times the  current-carrying capacity for that cable clipped direct to a surface and open (Reference Method C).

Where a cable is to be  totally surrounded by thermal  insulation for less than 0.5m the current-carrying capacity of the cable shall be  reduced appropriately depending on the size of cable, length  in  insulation and thermal  properties of the  insulation.  The  derating factors  in Table  52.2  are appropriate  to  conductor sizes  up  to  10mm²  in  thermal insulation having a thermal  conductivity (λ)  greater than 0.04 W^-1m·•K^-1

 

 

 

[A_L]

16 minutes ago, JSHarris said:

The  derating factors  in Table  52.2  are appropriate  to  conductor sizes  up  to  10mm²  in  thermal insulation having a thermal  conductivity (λ)  greater than 0.04 W^-1m·•K^-1

 

Do they actually mean 'less than' or are their other values for more insulating insulation?

[Jeremy Harris]

9 minutes ago, A_L said:

 

Do they actually mean 'less than' or are their other values for more insulating insulation?

 

 

I think they mean "greater than", with less thermally conductive insulation needing specific calculation of the derating factor based on cable temperature and cable insulation material. 

 

I've always tried to avoid putting cables in insulation if at all possible, not just for derating reasons but also because it's a PITA to work on later if cables are embedded in the stuff.

[A_L]

7 minutes ago, JSHarris said:

I think they mean "greater than", with less thermally conductive insulation needing specific calculation of the derating factor based on cable temperature and cable insulation material

 

So at what thermal conductance ( or other definition) does a material become an insulation requiring use of Table 52.2?

[Jeremy Harris]

Just now, A_L said:

 

So at what thermal conductance ( or other definition) does a material become an insulation requiring use of Table 52.2?

 

I'm not privy to the machinations within the IET that came up with these figures, I'm afraid!

 

If the conditions in Table 52.2 aren't met then the earlier paragraphs apply, so the derating factor is 0.5, or the factors in Appendix 4 apply.  Appendix 4 is several pages long, and includes calculations that should be used for different circumstances.  It's a bit too long for me to copy and paste to a post here, I'm afraid.

 

The general way the regs work is that they give a "quick and dirty" tabulated option that doesn't need calculations, plus a detailed option that requires a few sums in order to derive a valid answer.  Most of the time electricians try and stick within the simplified tabulated guidance, as it makes life simple, but it is equally valid to calculate factors using the methods given in Appendix 4.

 

 

 

 

[PeterW]

1 hour ago, AnonymousBosch said:

 

Why , why, why do companies even attempt to trade without even a cursory look at relevant guidelines? Why?

 

Because knowledge costs money, and it takes time... which also costs money...

 

When you look at the costs of just documentation for standards, it can soon mount up and they are probably working on the basis of a little bit of knowledge is a dangerous thing...

[andyscotland]

3 hours ago, ProDave said:

Where it says wires encased in their insulation "will not cause the wire temperature to exceed safety limits"

 

I actually think the crucial sentence in that PDF is on the next page : "I presently know of no reason why electrical wiring installed in accordance with the Electrical Safety Code will not operate safely in buildings where the thermal insulation is of the Icynene type".

 

I found a copy of the 2012 edition of the Canadian Electrical Safety Code online and from a cursory search it says:

 

Quote

2-122 Use of thermal insulation

(1) Where the hollow spaces between studding, joists, or rafters of buildings are to be filled with thermal insulation, the following restrictions, as applicable, shall apply to the installation of electrical wiring in such spaces: (a) special care shall be taken to ensure that conductor insulation temperatures are not exceeded due either to mutual heating of adjacent conductors or cables or to reduced heat dissipation through the thermal insulation

 

I haven't done a detailed look at their cable tables etc so I don't know if they specify in the same detail as BS7671, or if they leave it to the installer, but it's fairly clear they require precautions against overheating. And they probably did back in 1987 when that letter was written.

 

Therefore I read the electrical inspector's letter as meaning "there's no reason why Icynene poses any specific issue beyond what you'd have to consider with any sort of thermal insulation". Not "Icynene magically absorbs and disperses heat from the cable even though its entire function is to do the opposite of that with all other heat sources". Somewhere along the way someone has misunderstood, or misrepresented the advice.

 

Possibly if their recommended detail is that cables go in at first fix then you could (in some constructions) treat the cable as adjacent to a conductive surface at outside air temperature, rather than as being enclosed in insulation. I actually think that's marginal given the spray foam is likely to get most of the way round the cable, unless you had it in square ducting or whatever. But either way you'd definitely have to make some allowance to derate the cable from its free-air value.

 

1 hour ago, JSHarris said:

May be that some companies are just importing products from countries with different regulations?

The regs here haven't changed significantly for years with respect to cables in insulation.  This is from the current regs (BS7671:2018):

 

I think that's quite a charitable view. I'd be very surprised if many developed countries don't have similar regulations, albeit varyingly proscriptive/detailed. It's basic electrical science that one of the key factors in choosing a cable size is the heating effect of the current passing through and the effect of the resultant temperature on the adjacent building materials and the conductor/sheathing/electrical insulation of the cable itself. It's also basic physics that wrapping it in insulation vs hanging it in the open air will have different effects on that. In the nitty gritty of 7671 you're even supposed to allow for things like solar gain on cables if applicable. Hence, of course, why the regs here haven't changed significantly for a long time - the science of electrical heating is fairly well understood so there's not likely to be much need for change.

 

51 minutes ago, A_L said:

So at what thermal conductance ( or other definition) does a material become an insulation requiring use of Table 52.2?

 

Very good question. As far as I can see "thermal insulation" is not actually defined.

 

That said the "reference methods" that are used for the quick-and-dirty tables of pre-calculated values @JSHarris mentioned tend to either specify the cable being at least partly in open air, or in "masonry, brickwork, concrete, plaster or the like (other than thermally insulating materials)" or in "thermally insulating wall / ceiling etc".

 

So I'd say it's reasonable to use the non-insulated values for materials that are close to the performance of bog-standard old-fashioned masonry etc. Anything less conductive than that is probably outside the parameters those values were calculated for. So you'd either need to take the easy route and use the "thermally insulating" construction values, or if that produced a massively oversized cable or you had time to kill, work it out from first principles.

[Gone West]

On 25/09/2019 at 09:20, ProDave said:

Interresting to know what others who used Icynene (or similar) did? Did they do as they say, or did your electrian raise concerns and fit larger cables?

I ran all my cables in 32mm round conduit in the Icynene and derated them accordingly as sheathed cables in conduit in insulation.