Cavity insulation, EPS and cables

[Roger440]

Im pondering my insulation options in my newly aquired barn. 

 

Bizzarely, it has a cavity wall. Block inner and outer.

 

So, i was considering EPS beads. However, the previous owner put 90% of the elecrrical cabling in the cavity.

 

The internet says covering cables in insulation is bad and causes embrittlement.

 

Just how real is this problem?

 

Is it likely to be a problem in my lifetime?

 

Thoughts?

[ProDave]

Presumably you will be rewiring so is it even relevant?

 

[Roger440]

1 minute ago, ProDave said:

Presumably you will be rewiring so is it even relevant?

 

 

No re-wiring. Its 20 years old. And theres heaps of it. Chap went bonkers on electrics.

 

[Radian]

From my own research, plasticiser migration is a thing but I don't think it's a huge deal. Here's a learned document detailing the issue. OK, that's from New Zealand in 1988, but demonstrates how slightly arcane the issue is. I still own a house (that I rent out) that was built with EPS bead filled cavities back in 1986 and with extensions either side of the central "box" house, there are plenty of cables crossing the cavities. Admittedly these are mostly only exposed to the width of the cavity but all I've ever seen is a slight tackiness develop on the surface of the cable. No perceptible brittleness and it didn't penetrate to any noticeable degree.

 

My house was recently injected with EPS beads and I quizzed the surveyor about the cables I have crossing cavities (everything from the CU goes through an internal cavity wall) and he confirmed for me that it wasn't recognised as a problem with graphite coated beads.

 

BUT the more significant issue is the derating of the current carrying capacity of the cable. I would expect you could mitigate this by restricting the use of the circuits i.e. use 16A MCB instead of 32A and maybe re-wire any higher loading items like oven using surface conduit. If he went bonkers on electrics, might it imply that already have a degree of over-capacity? With greater efficiencies in just about every appliance these days, it may not need anything doing to address the heating issues.

 

But I shouldn't be giving the last word on the matter. I'd be interested to read what other people think about it.

[Spreadsheetman]

Interesting topic since I need to get the cavities insulated on the 70’s house I recently bought. The main incoming feed cables from meter to consumer unit run in the cavity, so I didn’t think eps bead was an option due to the pvc insulation issues.

[Roger440]

1 hour ago, Radian said:

From my own research, plasticiser migration is a thing but I don't think it's a huge deal. Here's a learned document detailing the issue. OK, that's from New Zealand in 1988, but demonstrates how slightly arcane the issue is. I still own a house (that I rent out) that was built with EPS bead filled cavities back in 1986 and with extensions either side of the central "box" house, there are plenty of cables crossing the cavities. Admittedly these are mostly only exposed to the width of the cavity but all I've ever seen is a slight tackiness develop on the surface of the cable. No perceptible brittleness and it didn't penetrate to any noticeable degree.

 

My house was recently injected with EPS beads and I quizzed the surveyor about the cables I have crossing cavities (everything from the CU goes through an internal cavity wall) and he confirmed for me that it wasn't recognised as a problem with graphite coated beads.

 

BUT the more significant issue is the derating of the current carrying capacity of the cable. I would expect you could mitigate this by restricting the use of the circuits i.e. use 16A MCB instead of 32A and maybe re-wire any higher loading items like oven using surface conduit. If he went bonkers on electrics, might it imply that already have a degree of over-capacity? With greater efficiencies in just about every appliance these days, it may not need anything doing to address the heating issues.

 

But I shouldn't be giving the last word on the matter. I'd be interested to read what other people think about it.

 

Interesting that graphite coated is ok. What are the benefits of graphite coated aside from this?

 

Yes, well aware of the derating of cables. Whilst he went a bit mad, im not sure its over rated as such. I think i would rewire the compressor and extract fan circuits as these are current hungry and for long periods of time.

 

Good idea on the breakers.

 

Sadly, however, ive not managed to find the incoming supply. Pretty sure thats in the cavity too!

[Nickfromwales]

You cannot have EPS in contact with PVC electrical cables.

[Roger440]

2 minutes ago, Nickfromwales said:

You cannot have EPS in contact with PVC electrical cables.

 

Yes, but why not?

 

Is it really a problem. What will actually happen in the next 25 years?

 

And what about graphite coated as per post above?

[ProDave]

Forget the plasticiser issue. Nobody has yet mentioned the need to derate cables enclosed in insulation, so if you are not thinking of rewiring you might be.

 

When you say cables in the cavity, do you just mean passing through?  That is probably okay.  Or do you mean cables dropped down the cavity and traveling long distances?

[Roger440]

12 minutes ago, ProDave said:

Forget the plasticiser issue. Nobody has yet mentioned the need to derate cables enclosed in insulation, so if you are not thinking of rewiring you might be.

 

When you say cables in the cavity, do you just mean passing through?  That is probably okay.  Or do you mean cables dropped down the cavity and traveling long distances?

 

Err radian did, as did i. Up there ^^^

 

Its ALL in the cavity. Literally everything. Unless it the lighting on the roof.

 

Rewiring on the scale involved isnt really an option. Building is 75 x 40 ft. Wiring, sockets etc, all the way round!

 

 

[Radian]

I can't find any technical info on the graphite coating other than that it reduces the thermal conductivity. But it totally transforms the beads. You get very messy hands (the guys that injected it looked like they'd just come up from a Welsh coal mine) and the surveyor specifically said that PVC cables were safe with graphite beads in response to my question. This was documented at the time as a "customer note" along with my concern about matching mortar colour (which admitedly could have been done better). Now it may have been BS, but I did a lot of due diligence on the company - and the guy was a proper jobsworth. Some of the checks were plain silly.

[Roger440]

4 minutes ago, Radian said:

I can't find any technical info on the graphite coating other than that it reduces the thermal conductivity. But it totally transforms the beads. You get very messy hands (the guys that injected it looked like they'd just come up from a Welsh coal mine) and the surveyor specifically said that PVC cables were safe with graphite beads in response to my question. This was documented at the time as a "customer note" along with my concern about matching mortar colour (which admitedly could have been done better). Now it may have been BS, but I did a lot of due diligence on the company - and the guy was a proper jobsworth. Some of the checks were plain silly.

 

Tranforms in what way though. Sorry if im being dense.

[Radian]

12 hours ago, Roger440 said:

Tranforms in what way though. Sorry if im being dense.

Perhaps 'transform' is the wrong way to describe it. I'm used to the white poly beads in my 80's house which had no binder so pour out of any opening. The graphite beads were injected with a binder and form a dark grey solid mass. I must check the electrical conductivity out of curiosity. It could be that they also create a Faraday cage!

[ProDave]

14 hours ago, Roger440 said:

 

Err radian did, as did i. Up there ^^^

 

Its ALL in the cavity. Literally everything. Unless it the lighting on the roof.

 

Rewiring on the scale involved isnt really an option. Building is 75 x 40 ft. Wiring, sockets etc, all the way round!

 

 

Then I would NOT fill the cavity with any sort of insulation.

[Radian]

3 hours ago, ProDave said:

Then I would NOT fill the cavity with any sort of insulation.

 

That may indeed be sensible blanket advice to offer... But in the interests of having an open technical discussion, I'm going to exercise my right to disagree. In engineering terms, there are just a few known factors to consider. If a workable solution that ensures electrical safety and an improvement to heat insulation can be found, then why not use it?

 

BS7671  regulation 523.7 identifies corrections to be made for a cable which, through any part of its run, passes through thermal insulation. The symbol for the correction factor for thermal insulation is Ci and approaches a limit of 0.5 as the encapsulated length becomes greater than 500mm. Hence my suggestion to halve all the breaker ratings.

 

I would also add that blown-in EPS bead cavity fill is far from being an air-tight insulator. Both convection and conduction will be taking place so reducing the heating effects on the cables when compared to solid fill.

 

As a sanity check, it's not exactly as if cable heating results in instant thermal runaway: R=R_initial(1+α(t_final-t_initial)) where α is the temperature coefficient for resistivity i.e. 3.9x10^-3 for copper. plugging in a temperature rise of 50^oC would increase the resistance of a (unrealistically high) 1 Ohm cable to 1.195 Ohms.  BS7671 specifies a maximum volt drop of 3% for lighting (6.9V) or 5% for other uses (11.5V) so if that 1 Ohm cable was on a 6A lighting circuit, the volt drop would increase by 1.17V However, 1.5kW of lighting is no longer the norm so even an extreme example is looking like being far from a serious issue.

[ProDave]

Here would be an interesting experiment for someone with lots of time.

 

Take a bit of ordinary t&e cable, load it to it's maximum rating and measure it's temperature (some form of probe attached to it)

 

Then bury in in the middle of a load of EPC beads no more than 100mm wide (or whatever your cavity width is) and repeat the load test and see how hot it gets.

 

Wiring regs talk about cables "in insulation"  But there is a big difference between a cable enclosed in the middle of 300mm of rockwool and one enclised in the middle of 100mm or less of EPS beads.

 

Yes you could derate a lot of the circuit breakers, but not on things like cooker or shower circuits.

 

I think the issue is not overheating and increasing volt drop, but overheating and melting the cable.  A rise of 50 degrees C would be very bad for PVC.

[Roger440]

5 hours ago, ProDave said:

Then I would NOT fill the cavity with any sort of insulation.

 

Ok, i follow the logic. But i still have the probem of insulating it. And every other option will be mad money. 

 

 

[Roger440]

14 minutes ago, ProDave said:

Here would be an interesting experiment for someone with lots of time.

 

 

 

Hmmm, thats definitely not me!

[Radian]

1 minute ago, ProDave said:

Here would be an interesting experiment for someone with lots of time.

 

Sounds like a "me" 😄

 

2 minutes ago, ProDave said:

Wiring regs talk about cables "in insulation"  But there is a big difference between a cable enclosed in the middle of 300mm of rockwool and one enclised in the middle of 100mm or less of EPS beads.

This is where it gets a bit more hazy. I'm pretty sure the cable would actually experience greater heating in rockwool on account of it being less air permeable. But that's just a hunch. Another experiment perhaps.

[Iceverge]

Blown mineral wool, closed cell foam or maybe even poured in vermiculite are alternatives that wouldn't have the plasticiser issue. 

 

I know of a house that had cables in the cavity so the EPS bead installer wouldn't pump it. 

 

It was done with what looks like open cell foam. It completely crumbles to dust when you pinch it. However has made the house much warmer and AFAIK no issues with the electrics so far. 

[Radian]

Quote

The rate of plasticiser migration is determined by many factors but is strongly affected by the contact area
between the cable and the thermal insulating material. The migration process would be expected to occur
over a relatively long time frame, there is anecdotal evidence that rapid migration can occur in polystyrene
block houses, portable buildings and chillers. This is due mainly to the large contact area between the
insulating material and the cable. 

https://nationalpolystyrene.com.au/wp-content/uploads/2020/11/PVC-Cables-in-Contact-with-Polystyrene-or-Bitumen-2.pdf

 

I don't doubt that a pvc cable sitting on a sheet of pure white polystyrene would degrade over time. I've seen the kind of effect it creates first-hand. But I think the key to its safety when used with graphite coated beads is in the statement above: "strongly affected by the contact area". The beads make contact at the tiny tangents on the spherical beads and even then, are buffered by the graphite shell.

 

@Onoff started a thread on this topic a while ago, but I couldn't see any reference to graphite coated EPS in it. In fact, nowhere on the internet can I find such a discussion.

 

 

[Roger440]

22 hours ago, Iceverge said:

Blown mineral wool, closed cell foam or maybe even poured in vermiculite are alternatives that wouldn't have the plasticiser issue. 

 

I know of a house that had cables in the cavity so the EPS bead installer wouldn't pump it. 

 

It was done with what looks like open cell foam. It completely crumbles to dust when you pinch it. However has made the house much warmer and AFAIK no issues with the electrics so far. 

 

Mineral wool is out as an option. Too much risk of wind driven rain.

 

Closed cell foam would work, but bankruptcy would follow with that . Likewise with vermiculite.

 

Any idea what the open cell foam was?

[Roger440]

21 hours ago, Radian said:

https://nationalpolystyrene.com.au/wp-content/uploads/2020/11/PVC-Cables-in-Contact-with-Polystyrene-or-Bitumen-2.pdf

 

I don't doubt that a pvc cable sitting on a sheet of pure white polystyrene would degrade over time. I've seen the kind of effect it creates first-hand. But I think the key to its safety when used with graphite coated beads is in the statement above: "strongly affected by the contact area". The beads make contact at the tiny tangents on the spherical beads and even then, are buffered by the graphite shell.

 

@Onoff started a thread on this topic a while ago, but I couldn't see any reference to graphite coated EPS in it. In fact, nowhere on the internet can I find such a discussion.

 

 

 

All interesting stuff, but as you say, no reference to graphite coated beads.

 

That seems to be the missing piece of info, as cleary, on a cost basis, its the winner.

 

 

[Conor]

I had this debate with my spark in our build. They were running cables directly against the EPS roof panels and I called him out on it. He was of the view that it was ok, unless they were in a potential over heating situation. I impressed the whole plasticiser migration thing, and he was adamant there was no issue. As it happened, he was going though his NICEIC recertification and his assessor visited the site and was of the same view, not a known issue in their industry. 

 

Also, it seems the brittleing of cables is only an issue if they move around and crack... So for hidden cables not an issue anyway.

Edited November 26, 2022 by Conor

[Roger440]

Still pondering this. Given the complications, ive been costing up insulating inside the inner wall with rockwall and steel cladding sheets. Got a good handle on the cost of that.

 

The question is, whats the cost of installation EPS beads? (given its not really a DIY job)

 

Does anyone have a recentish approx price per sqm?